Vision Science

 

These sections are oriented toward understanding and using portable lighting to illuminate outdoor surfaces for "better vision"

1. How Eyesight Works

     1a. Introduction To Vision

     1b. Color Vision

     1c. Dark-Adapted Vision

Contents 

2. Measuring Light: What is Important

     2a. Terminology and Meaning (maybe not what you thought)

     2b. Vision and sound perception have analogous characteristics

     2c. Light Quality Measurements

     2d. Multiple Light Sources

3. Using Outdoor Illumination - What You Need to Know About Illuminating Natural Surfaces

* Vision Science is a broad descriptor. It covers how you obtain and interpret visual images

1. How Eyesight Works

 1a. Introduction To Vision

Your vision is amazing. You can see far more than you probably realize, but you also see objects differently than you may realize.

In this introduction we will review the simplest aspects of eye function and visual response relative to our objective of better vision in the dark using illumination.

 

Our objective in this section of the website is to make "what is important to know" easy for anyone to understand and to help almost anyone understand how to improve their vision in darkness, and to better select and use illumination..

 

There is substantial additional detail behind each tiny part of our explanations in this website you can research, but we worked hard to avoid simplifications that might misdirect from our objective. There is a huge amount of good literature in all these subject areas, but there is also quite of bit of just-plain-wrong and misleading information out there on the Internet from even seemingly credible sources. The basics you need to know are not that complicated that can help you avoid common mistakes. 

Illumination for Vision Basics

First, a few quick definitions:

Illumination is the luminous flux per unit area on an intercepting surface at any given point

Irradiance is the flux of light striking a surface, measured in Radiant Light Flux (Power)/unit area. This effectively means amount of light power arriving on a surface.

 

To make sure we have light and vision in perspective, let's first quickly review how the interference patterns of light are created when objects are illuminated. These light patterns are what our eye and brain will perceive and interpret as images. For the most part, only the wavelengths in the light illuminating objects can be reflected and seen. 

Light is typically reflected from most objects other than mirrors in all directions​, otherwise you would not be able to see objects from a great many potential eye or camera location.

Pure light colors are narrow ranges of a visible wavelength like are produced by lasers or single color LEDs (not white). These are only a small part of a color range. Red or blue LEDs effectively output only about 25% of the red or blue spectrum respectively. Some colors are only seen as mixtures of wavelengths (e.g., magenta is not a single wavelength color, it is only a mixture of violet or blue and red wavelength light), and some color ranges such as yellow can be either a single wavelength or a mixture (Red and green light mix to appear as yellow light, as is often done in traffic lights, typical color TVs, computer monitors, phone screens, and RGB color-changing LED bulbs).  

 

Most of the thousands of natural objects that we tested reflected at least a small amount of all visible wavelength ranges, although the overall spectral power distributions varied greatly. The most difficult-to-see objects such as very black earth, some molds, or lampblack (fine soot) absorbed almost all light, but even these materials reflected considerable visible deep-reds. Few of these black materials appear red to the eye.

 

Our eye-brain system usually needs a nearby reference color surface (or background reference) at the same time to properly recognize most colors or grays as we are best at "differential" color recognition. This is especially true in low luminance situations. Also, a very small amount of reflected or ambient mid-spectral light components can make deeper reds appear gray. Regardless of red color recognition, almost everyone sees deep-red light and these deep-reds are important for assessing shapes, patterns, and textures of darker natural surfaces.

How the eye captures and uses light

   

Light reflects from objects in all forward directions from most objects then enters the eye. The eye captures a very small amount of the light reflected from the illuminated object. Also, the illuminated area typically covers a much larger area than one specific object.

This is important to understand because the percentage of light your eye captures from a specific object can easily be under a millionth of the light from your lamp. Ways to improve the light captured for vision for a fixed amount of light:

1) Getting closer to the objects of interest with the light source,

2) Focusing the light on the objects of interest,

3) Getting closer, or

4) Use lenses to capture more light to you eyes such as binoculars. If you also become dark-adapted, your ability to make image from a smaller amount of light can improve by factors of 1,000 -to-1 million.

5) Become dark-adapted to increase the amount of light to the retina and eye Cone+Rod sensitivity

While the eye is a fascinating optical sensor, it is very important to keep in mind that a huge component of your vision takes place in the image processor portion of your brain. Understanding how this all works is important to better utilizing any illumination or vision enhancing system.  

In the PHOTORECEPTOR CELLS graphic below showing how the eye works, light illuminates and object (the owl. Some light colors are absorbed, but some light also reflects in many directions. Some of this reflected light enters the eye and  is focused onto the retina. In this example, the light focuses onto the fovial spot where almost all the color sensing cones are located (most of the retina contains rods that are only active for vision in low light). In the lower left corner of the graphic, you see the response vs. wavelength for each of the eye's 3 type cones and the eye's rods.

 

1b) COLOR VISION 

 

Color vision is determined by the 3 type cones and these are located in a tiny 1.5mm diameter spot on the retina as shown in the middle and lower middle of the above "Photoreceptor Cells" graphic.

 

Each eye typically has about 6-7 million total cones. This is fewer sensor pixels than even a typical smart phone camera, but there is a lot else going on the eye-brain system such as unconscious scanning of both eyes and image storage. This all effectively creates the impression of far higher resolution (although quite a bit of your perception of a large continuous high resolution view is also calculated or imagined).

 

Some optical illusions are based on this aspect of your perception of images often being based on a "calculated" image from the eye.  For instance, you do not notice the blind spot in the back of each eye unless you do an experiment to force your brain to recognize it.

In medium-low to high light intensities, only your eyes cones are providing images to your brain. Your eye's  vast number of super-light-responsive rods are turned off for imaging and "out of the picture".

 

Cones-Only vision is called Photopic vision. This is the state of vision you use most of the time, and probably now while you are reading text. 

 

The relative light response vs. wavelength for each type cone is provided in the bottom left of the chart.  Before we discuss each type cone, it is important to notice that each cone has a very wide response vs. wavelength range. All your eye's cones are responsive to green and yellow, which is a major reason why the eye sees yellow-green photons appearing far "brighter" than red or blue photons. 

 

Yellow-green light appears about 10 times brighter than mid-red or mid-blue light for the same amount of actual radiant light power. However, without other parts of the spectrum, considerable detail about objects is lost. We will breifly discuss to fallacy of using brightness as a metric and "brightness" vs "amount of light" in the "Light Metrics" section of this website.

There are differences in cone type sensitivity, relative quantity or each type cone, and the way neural pathways are organized behind the receptors. There is a complex matrix of reasons why these arrangements probably exist for most humans and it appears to have little to do with what colors are most "important", but that is the subject of a greater depth future discussion. There has been much research on how color eyesight may have evolved and many other aspects of the eye's chemistry and physics. Further understanding this "Why" beyond what is covered in this section is interesting, but probably of lesser value to your near-term selection and use of better lighting than what is in this

review. 

Types of Cones:

The  S Cones (Shorter wavelength) peak is at about 420nm which appears as violet, but only about 2-4% of your cones are S type.

The  M Cones (Medium wavelength) peak is at about 534nm which appears as green. About 30-34% of your cones are M type.

The L Comes (Long wavelength) peak is at about 584nm which appears yellow. About 62-66% of your cones are L type.

No red cones?   So how can I see red?

Your brain's image processor takes the relative values from all 3 cone types and subconsciously calculates colors. Red is a calculated color by the brain. The L cones do detect even deep-red light, including near infrared. The cones are just less sensitive to red and mostly detect yellow. If there is almost no response from the S and M cones but the L cones are active, then the brain knows red light must be present. Red is very important and very prevalent in nature, so your eyes 3 cones and brain help you "effectively" see red. 

 

As a result of many colors being calculated by the brain, it is easy to fool the eye regarding color in generally predictable ways.

 

TVs and phone screens fool your eyes into seeing many colors with only 3 colors, and color printers can do this with as few as 4 different colors that are used to fool the eye into seeing 16 million or more colors (8 bits/color). For example, red and green light mixes to appear yellow to the eye even though there is almost no yellow present (this works similar for the camera sensor).  

But, put a true-mid-yellow reflecting object under an RGB lamp and watch it gray out.  There are big spectral gaps between the red, green, and blue pixels in a TV or phone screen, otherwise the display screen colors would appear only as "pastels".

Illumination of surfaces to show their ture colors are very different processes than looking at a lighted screen with generated RGB mix colors. All wavelengths may potentially be reflected from a natural surface, not just designed and calculated colors mixed according to a human standard.

RGB Color Changing LED Light Bulbs have the same optical weakness as using a phone screen for illumination, and can even be worse. Most use narrow spectrum Red, Green, & Blue LEDs and skip more of the visible spectrum than a cool-white or neutral-white LED. Multiplexing the ratio of gray levels increases the number of color shades, does not increase the spectral color ranges available!  These LEDs are for "decorative or mood lighting" only, and are poor illuminators. Even adding a white LED chip to become RGBW leaves this type lamp wanting. 

TVs and phone screen displays have similar appearing red-green-blue (RGB) color dot arrays like are shown above for a camera sensor. But, in a display the light is emitted from each of the color sub-pixel elements. These are the only colors the camera sees or your display emits for you to see. 

Notice that these cone peak light responses are quite different that the Red-Green-Blue (RGB) pixels of phone or TV screen. The camera sensor can directly see red and the display produces what is usually an orange-red, while your eye's L cones peak at yellow (and most of your eye's cones are L-Cones). The camera or display has a sensitivity peak, but your eye's S-Cones actually has a violet peak sensitivity), or the pixel filters in camera sensors.

 

There are many computations and correction factors used to mitigate these effects to photos and videos appear similar to what you would have seen, but each different new light source, environment with different reflected light from the surroundings, printer or display device often requires a different calculation.

 

Nature uses ALL coloring methods, so you need a light source that will reveal all colors when color and detail matter.

Cameras and Eyes are even more different when Dark-Adaptated

Another important point is that human or most animal eyes and cameras have very different dark-adapted modes. We have seen no cameras with cyan peak sensitivity night vision modes that work similar to the dark-adapted human or animal eyes. There are light intensifiers, high ISO cameras, IR cameras that extend even out to very-long wavelength thermal imaging, and there are many near-infrared (NIR) night-vision cameras that use NIR LEDs for illumination (typically using over-800nm wavelength LED light). However, these have very different spectral sensitivity ranges than your eye's rods. Surfaces absorb, reflect or scatter light quite differently each spectral range (this means their images appear quite different from what you would see when full dark-adapted).

In most of our surface spectral measurements during the past 3 years we also took many measurements in the 700-1100nm NIR spectal range. Many surfaces are highly reflective in this range. There are many NIR wildlife and security cameras (we have a several), and there is a whole photographic art form built around NIR images, but this is outside the spectral range of this direct eye sight discussion.

Higher power modes of Cyradiance technology light and our daylight simulation spectra are not-surprisingly similar to incandescent light or daylight, respectively. We do use more relative red and cyan spectral light than is in daylight to help the human eye see more detail and see further at night. ActiveRed filtered light and low-light or red-enhanced Cyradiance technology light modes can create interesting photographic images, but don't expect the photos taken using night-vision mode lighting for dark-adapted vision to look like what your eyes saw without some post processing work. Do expect much more detailed images than you would have gotten using red LEDs.

Nulumina's Cyradiance illuminators were primarily designed to improve human color vision of almost all objects, with a focus on surfaces that can be most important when you are hiking, running, biking, or most anything else outdoors on natural surfaces.

Nulumina's illuminators happen to be excellent for photography due to their high CRI values, even though that was not their primary purpose.

1c. Dark-Adapted Vision

 

Many people now live in an extraordinarily lighted world where huge amounts of light seem to be almost everywhere at any time of night. Our eye's rods do not even become mostly active until after typically about 20-30 minutes or longer in darkness, so unlike people even 30 years ago most cities and our homes our eye's rods that constitute 95% of our eye's image sensors (that are about 100X as responsive to light as the eye's cones) might hardly ever even be used . The eye's rods might be active when we first wake at night, but even a direct look at a typical LED night light in a room can turns the eye's rods back off in 1- 2 seconds. People can go years without every really using one of the most powerful aspects of their vision.

 

People that often get away from towns and cities at night know this. Anyone considering advanced lighting for outdoor use such as ours is probably already well aware of the fact that their eyes adapt to low light, and that they can see amazingly well things in low light if given the chance.  

We wanted to enable broad-color vision with enough intensity to allow for high visual acuity, but to design the physical lamps, optical and spectral systems to conserve power and allow an option for our magnificent dark-adapted vision to do wonders and let us see far more of the detail in our surroundings and improve our situational awareness using minimal battery power. 

Dark-adapted vision happens in stages:

The time required for these dark adaptation transitions vary from person to person individually, that amount of light exposure you experienced during the day, the conditions just before you enter darkness, and the dark environment itself. In this example we start at normal daylight intensity. It takes longer to dark-adapt from light intensity situations near the upper-range of our eye's light tolerance. 

1st:   As you exit a normal daylight environment your pupils enlarge to let in more light. Near maximum pupil opening size can happen quite fast in 15 seconds or less (constriction is much faster than dilation). This can improve your light sensitivity by 10X, but your visual acuity is reduced just like going to a lower f-stop on a camera.

2nd:  Then, the eye's cones increase in sensitivity, but only your eye's 3 type color cone's provide images. This sensitivity increase happens relatively fast. After about 10 minutes in low light your cones can be mostly "cone" dark-adapted, increasing color light sensitivity by a factor of over 100. Your eye's rods are just starting to turn on after about 10 minutes in low light or mostly red light.

3rd:  As your eye's rods continue to slowly turn on, your ability to see images in low-light can increase by another factor of 1000-100,000. This can take an additional 20-30 minutes to become mostly dark-adapted for a total time in darkness or low-light of about 30-40 minutes. The time for almost all rods to activate typically takes 40 minutes or more in darkness or very low light (since your eye's rods are almost-insensitive to red light over 620nm, red light can be almost like darkness for rod activation). 

 

Dark-adaptation can take longer, depending on multiple factors such as your prior light exposure and your low light environment.  

 

At the lowest light levels when only the eye's rods are imaging, the world can appear shades of cyan and black. Because the light intensity is below our cones light perception, other colors are lost. (Rods happen to be most sensitive to cyan light in the 490-510nm range). 

 

It is very important to remember, it only take 1-2 seconds of bright light mid spectral range light exposure to turn the rods off and make you restart dark-adaptation. 

 

The typical total human vision range can enable a 100,000,000 ratio change in your ability to see images between high or low light intensity situations. The following table summarizes these effects.

Using your dark adaptation can be very useful, in addition to saving on battery power. Your ability to see far away light sources is greatly improved, and since Nulumina's Cyradiance light contains boosted cyan spectral range light, your long distance vision can exceed that of lamps using 5-10X the battery power.  Just be very careful to not look at the Cyradiance light, or at pale-colored or highly reflective surfaces close up or you will likely need to restart your dark-adaptation. 

USING ILLUMINATION IN THE 3 STATES OF HUMAN VISION

Photopic Vision occurs when vision is entirely mediated by cones.

Cones only work in moderately-low to bright light (bright moonlight to bright sunlight).


Cyradiance™ technology is powered by unique LEDs that emit increased Red and Deep-Red light where your eyes’ cones need a boost, so objects reflecting those colors become far-more visible, while still providing ALL other colors in the visible light spectrum from deep-blue to deep-red. The OwlSight can add a wide-violet spectrum capability for sunlight-like spectra to maximize your photoic vision range. You can better perceive or detect more types of objects compared to typical super-bright LED flashlights that output mostly yellow-green light, but relatively little red or cyan light. Photopic vision requires the greatest amount of light power.  

Use your photopic vision mode with the OwlSights‘ Modes 3 or 4 closer than 60m (183ft on clear nights) and when you want the greatest color detail and are not dark-adapted, or use Mode 2 closer than ~13m (40ft). This distance can increase if other lights are in the vicinity such as the moon, LegLights™, or your partners’ lamps.

Scotopic Vision occurs at low to very-low light levels (moonless to dim moonlight) when vision is entirely mediated by rods. Rods do not image in normal daylight, and rods “turn off” quickly when exposed to medium-to-high light intensities, and then can take >20 minutes to “turn back on”. Your eyes’ rods can be over 100X more light sensitive than cones. Since red light is virtually not visible to your rods, red light does not interferre with night vision, however red light sources only provides cone-mediated vision of objects up-close that reflect the specific red wavelengths you provide. Dark-adapted pilots seeking distant lighted objects use red light for seeing
instruments close-up. However, red-only light is not very useful when tekking unless you also are looking for distant lights, or there is another light illuminating your path.

Mesopic Vision occurs in moderately low-light (dim moonlight to dim twilight) when both rods and cones work together. Mesopic vision works best with an optimized light spectrum and correct intensity profile of light. Mesopic vision is the ideal night-vision vision state, as it makes optimal use of battery power while providing the greatest distance view plus color vision. For mesopic vision to work well, you need the right spectrum and beam profile. 

Cyradiance technology provides a cyan light peak so, once you become dark-adapted, your distance vision of the illuminated zone is greatly enhanced, extending your vision to distances beyond that of “super-bright” white light LED light sources requiring even 4X the battery power, and still enabling searches for distant dim lights. 

But, you must be careful to avoid looking directly into the light or illuminating objects closer than 5m (16ft) by the intense part of your spotlight if you wish to remain dark-adapted, unless you use the ActiveRed™ filter in modes 2, 3 or 4.  The ActiveRed filter provides a very small amount of broad spectrum light, so you can still see most type objects up close, but better stay dark-adapted when you are on a path where objects (e.g., branches) protrude closer than 5-6m into the middle of your spotlight beam. 

WHAT IS DIFFERENT ABOUT NOCTOURNAL ANIMAL VISION?

Many creatures have significantly advanced abilities to see using little light. We will not include animals that use mostly sound, thermal variations, surface vibration, or smell to effectively  "see" in this short discussion.

 

The main advantages for nocturnal animals result from a high percent of dark-adaptation rods for vision, a higher ratio of neural pathways per rod to transmit data to the brain, sometimes closer packed rods, large eye sockets, and a reflective back retina so light gets 2 chances to interact with the their eyes rods and cones.  The price paid for better night vision is often poorer color vision.

Uniquely, you can switch on your own light source (now even with multiple useful spectra including enhanced UVA), so your eyesight can effectively exceed the capability of any nocturnal animal. Pick the correct spectrum, intensity, matrix of light sources, get dark-adapted, and you can get around in darkness better than any nocturnal animal that mostly uses "eyesight".

 

A downside to carrying your own light is that you cannot easily sneak up on other creatures when using artificial light since they also see the light. Mostly red light helps you be much less obtrusive, since (like humans) animal's rods are barely responsive to mid-red or deep-red light , but they have cones and can see red light so you are only "less" obtrusive. But, our objective here is just "great vision at night". 

For your covert nighttime operations, you will need other tools like NIR or IR cameras, image intensifiers, or other imaging tools.

  IMPORTANT REMINDERS: To stay dark-adapted, never look directly at any turned-on Cyradiance lamps.

Also, avoid shining headlamps or flashlights at up-close, light-color or highly-reflective surfaces.

      

Cyan spectrum light is great for long-distance dark-adapted night vision using minimal power because your eye's rods

are the most responsive to cyan light, but too much cyan light for even 1-second can turn most of your eye's rods off.

Quickly turn away or shut your eyes if these, or any other bright lamp is directed at your eyes to avoid re-starting dark-adaptation.

2. Light Metrics
 

2a. Terminology and meaning (maybe not what you thought!)

  Lumens Does not Mean What You Might Think

Lumens is percieved "brightness", not the "amount of "light"

 "Brightness" is not the amount of "radiated light power" 

 

There are many important metrics for lighting, but we will first focus on one set that is unfortunately often misunderstood and that has lead an industry to making many poor choices.

 

ILLUMINATION METRICS (mW “RADIANT FLUX POWER” vs. LUMENS OF “BRIGHTNESS”) 

Nulumina utilizes Radiant Flux (measured in Watts) as the primary measurement of total light output from our full-color spectrum lamps.   
“Radiant light output (radiant flux)” and “brightness” are very different terms, and it is important to understand the difference.

Radiant Flux (Watts):  Radiant flux measures the total light output power of a lamp at all wavelengths (This is different from lamp or LED electric input power). 


Light in the 390nm-720nm range is important for color vision and easily visible to most people. We consider this to be a full-visible light spectrum.

"Lumens" is NOT a direct measurement of amount of light as many people think. Lumens is determined by first taking an actual measurement total light from a light source at each wavelength (watts of radiant flux), and then convolving this measured value with this 1931 CIE eye response curve to come up with a "perceived brightness" number for a light source.

Brightness (measured in Lumens): “Brightness” is an approximation of the average eye’s perception of brightness of light from a lamp. Brightness is calculated from Radiant Flux measurements using an algorithm that reduces the values of visible violet, blue, and red radiant light power to under-5% of the same amount of yellow light when measured as lumens. The algorithim for lumens is based on  the CIE eye sensitivity curve published in 1931 which defined 555-556nm yellow green light as the brightness sensitivity peak for the photopic human vision (using only the eye’s cones in "not-dark adapted vision").  This yellow-green light is where human eyes are typically most responsive (Using only your eye's cones in moderate-to-bright light, NOT when you are dark-adapted).

 

There were several flaws in this 1931 standard that the CIE has attempted to correct over the past 85+ years with "brightness" standards that better represent the earth's diversity of humans, using  more reliable human experimental response procedures, better and varied light sources, and better object patterns with better characterized spectral reflectivity.  The ~555-556nm yellow-green center of human "brightness" perception has not significantly changed in newer standards, but the human visible color range into the deeper reds and violets, and the shape of the rest of the relative "brightness" perception vs wavelength curve has changed.

 

Still, "lumens" remains based on the old flawed CIE standard.  Unfortunately, when an indirect metric like "lumens" is used for many years, it can be difficult to replace. This 1932 CIE standard used to define "lumens" does still provide a gross approximation of how most humans generally perceive various light wavelengths as "relatively bright" vs. the actual measurement of the light power intensity.  

 

See our analogy of Audio and Vision in this section of our website to see why you should want the opposite of what is being done with headlamp and flashlight LED light spectra. In this analogy, maximizing brightness with mostly mid-spectrum yellow-green light for vision is like maximizing loudness for audio at the expense of quality and detail perception. You should want more relative light intensity at the spectral wavelengths where vision is weaker, if improving perception of visual detail is the objective.

So how did lumens become confused with amount of light from a lamp?

In the 1920's and 1930's, almost all home, street, and workplace lamps were glowing hot filaments (black body generators). These lamps all emitted quite a bit of wide-spectrum red light, so red was never a problem. Violet, blue, green, yellow spectral ranges were weak except at higher filament temperatures, so "light quality" tended to focus on higher temperature filament lamps with a broader spectrum for many years.

Because the brighter perceived part of the visible spectrum was in the green and yellow (and all lamps had similar shape spectra with red never being a problem), perceived brightness was an easy to understand "goodness" parameter for lighting.

 

From 1930 to 1990 you could compare "brightness" of filament bulbs and actually be comparing amount of light with minimal error because most filament light bulb spectra were all similar  (>80% of the market being filament with almost all the balance being fluorescent and gas discharge such as HPS even by the 1970s and 1980s). Fluorescent bulbs not black body generators, but had materials and manufacturing limitations that made going along with the old misunderstanding cost effective. 

 

For over 50 years you actually could compare the amount of light using brightness with minimal error since the light spectra for most filament bulbs were similar (other than low temperature decorative filament bulbs). Halogen bulbs just allow the temperature of the filament to be higher with decent filament life, so the violet-yellow part of the spectrum is relatively greater (brighter appearing), although they still waste a lot of energy as heat and non-visible infrared light. There still is considerable all-red-spectral-range light from halogen bulbs, which is why many people prefer halogen bulbs for deep diving because red light is depleted from seawater with increasing depth.

Brightness came to mean amount of light to most people, BUT not to scientists and manufacturers of light systems.  The real definition never changed. Brightness is a perception adjusted metric, not a actual amount of light measurement.

FYI: The "color temperature" metric was created based on the black body radiation characteristics temperature as a hot object like a filament (FYI: color temperature is irrelevant and even misleading for not-black-body light sources such as LEDs even though color temperature is still used as part of many LED product specifications. Many different spectra can create the same color temperature, often with bad results) . Higher was usually better because you got more of the rest of the spectrum 

LEDs are not black-body light generators like filament bulbs such as halogen bulbs or kypton-filled bulbs.  This is where many problems originate since we are still using metrics for LEDs that were created for filament bulbs over 80 years ago.

LEDs vs other types of human-created light sources

LEDs are solid state devices, that are fundamentally  different from all previous light sources (even different from electroluminescent lights).

LEDs are not light gas discharge lamps, such as sodium, neon, mercury (typical fluorescent bulbs)  and other similar bulbs, although typical fluorescent bulbs also use spectrum converting phosphors or dyes to generate other spectral ranges than uncoated fluorescent bulbs would provide, which is similar in concept to phosphors frequently used by white LEDs .  

What you really want to know for better vision using a light source for illumination is: 1) the spectrum of the light source (2) The radiant light power (Radiant flux in W or mW), and to know  the spectral response of what you plan to illuminate is a fit with your illumination spectra and state of vision. By state of vision here, we typically mean level of dark-adaptation. 

You typically get none of these 3 most important parameters with even the most expensive alternate headlamps and flashlights. 

Why do other headlamp and flashlight makers typically not provide this critical information?

2b. Light Quality Measuremements

There are several published metrics for color quality, but we will first concentrate on color rendering index or CRI and its application for  "illumination for vision" . CRI is a measurement that assesses how accurate colors will appear compared to a standard. CRI are mostly used for photography, but are useful for also assessing illumination light spectra for direct photopic vision (when used with other metrics).

There are quite a few types of Color Rendering Index (CRI) metrics for illumination, and some still in development. There are many resources available on line about CRI you can search and read about. If these terms are new to you, you might start searching "Color Rendering Index" with Wikipedia, and then continue your study to wherever your curiosity leads. 

Some of the newer CRI metrcis using many more and different reference points may be useful for your outdoor illumination  purposes, but they are less common as references and all the current CRI are designed around reproducing colors to a standard reference set, and not necessarily our goal of highlighting the greatest detail in surfaces. Some CRI metrics are for general vision with different references, and some CRI are mostly for photography, display, and broadcast. 

Being photonics technologists, getting even CRI Ra of 100 would not be difficult (we modify spectra by generating better light and light spectrum conversion, and not by wasting light energy with light blocking filters. Almost any spectra is obtainable with a combination of LEDs and color converters.). The reason we are typically CRI 95 ±3 on headlamps and flashlights and 88-92 on leglights, instead of targeting CRI Re and Ra of 99-100 is that our goal for our Precision Illuminators is to obtain the best "detail revealing vision" of surfaces matter most outdoors. But, we still also want crisp reference colors that are almost indistinguishable to most observers from what would be seen in daylight.  Therefore, we boosted the deeper reds a bit more than would be optimal for a CRI of 100 so that the detail in many of those darker brown and almost-black surfaces that can be hazards would be better revealed.

Cool and Nuetral white  LEDs used in other headlamps and flashlights have very poor CRI of 60-75. Some home and business LED lighting such as warm LED lights have better  CRI in the 80 or higher range, but almost all still lack the deeper reds and cyans you are likely to desire for dark rugged terrain use. There are a few specialized LEDs and combinations of LEDs that provide higher CRI, mostly for professional photography. One important aspect of a higher CRI is sufficient red spectral light, but red photons count as 1/10 or less the lumens of yellow light, so the industry mis-direction based on consumer confusion over the difference between brightness and amount of light and the ease of making poor light-quality, but high brightness LEDs using just a blue LED and a yellow phosphor has led to mostly poor CRI LEDs in the market. If you are reading text or walking on pavement, "brightness" is a fine standard to use, but you need to see the detail provided by all the red and cyan wavelengths on a rugged mountain trail even if you don't care about the aesthetics of seeing the colorful space around you at night.

The most used CRI is CRI Ra,  which uses an average measurement of 8 spectral colors to assess matching to sunlight or incandescent lights. This most-used and simplest metric under-represents the importance of violets and deep-reds in the spectrum, but this metric is still reasonable for estimating how many colors including most browns and reds will appear (except colors with significant potential violet or deep reds in their reflected spectra). A less used alternate metric is CRI Re. CRI Re increases the averaged color points to 15. We also frequently measured Re for our Cyradiance light has also shown very high Re values, within ±2 of the Ra value range on the same LEDs.

There are also a few other important color quality metrics besides CRI. Many are not very relevant for headlamps and flashlight for rugged outdoor use, but some do have  have relevance for outdoor personal lighting.

Two Other Interesting illumination Metrics:

 

There are many different illumination and imaging related metrics (mostly created for photography and video), and you do not need to know about most of them to see-better on your next hike, run, ride, night ski, hunt, or fishing trip.

 

It is a little disappointing that one of the potentially most misleading metrics (lumens of brightness) became one of the most commonly used and misunderstood values. In this very brief review, we will introduce you to few other common light quality metrics that have some merit here. You can use this as a starting point to search and learn more about light, if you wish. 

 

We assume your primary objective is for better vision and hazard avoidance outdoors. This is different from professional photographers and others that would typically use most available metrics. However, almost everyone also takes photos and videos on or off the trail. 

 

One useful metric that is mostly photography oriented, but has value for good vision is Gamut Area Index (GAI). It is a measure of visible color saturation potential from a light source.  This metric helps determine how a light spectrum will assess saturation and color discrimination. It also helps assess how saturated will certain saturated object colors are likely to appear. Too high or low can be a problem, but the GAI you seek depends on your objective.  Cyradiance light typically has a GAI of about 80-90 (Active Red is  different). This means objects under this illumination are not over-saturated, but appear properly saturated with very-good color discrimination.  

 

Another potentially important metric for outdoor personal lighting users is the S/P ratio. This metric helps you assess a light source's use for dark-adapted vs. normal vision.

This ratio of the Scotopic to Photopic response for a given light assesses how a light spectra can improve your ability to see both in low light dark-adapted and normal-high light intensity situations. Cyradiance light typically has a S/P value of 2.0-2.5, which is very good for dark-adapted vision!  Higher S/P requires a spectrum that does not show true colors as well when you are not dark-adapted.

 

You care because no matter how much light intensity you use, if you are dark-adapted you want to be able to see in the perimeter outside your primary light beam. A higher S/P tells you you can still see this in this less well intense region using the scattered light from the light beam, other light sources such as moonlight, or reflected light scattered from surfaces you are illuminating. Cyan light would give the highest S/P ratio, but even important cyan light needs to be balanced if you are to still see the other colors and detail you need. 

3. What is Important for Great Full-Color Illumination?

Other LED Headlamps and Flashlights seek the highest "brightness", but their makers care little about the other half of the light spectrum since that do not count as many "lumens" on a specification sheet. They never looked or cared at what wavelengths actual objects outdoors actually reflect. As it turns out, most hazards, terrain contours, and objects of interest that make the difference between a safe and enjoyable night trek and a risky trudge through the dark are more difficult to see using this faulty logic.

All-yellow light would have the highest "brightness". Other white  LEDs use blue LEDs with a yellow phosphor giving a narrow blue spectral peak, but most of the light energy is in the large yellow-green. The light appears white to the eye, but has little resemblance to the spectrum of sunlight. So, an LED maker playing a game of trying for the most lumens on a data sheet at the lowest cost gives you a blue peak and a yellow-green. If you do not know that lumens is not "amount of light" then you think you get more light.

 

What you get is more yellow light and less of the rest of the visible light spectrum. You dark-adapted vision is also mediocre.

This light is best for black and yellow dry grasses, most made made materials,  or black & white patterns such as text on white paper.

 

This is a poor quality light that appears "bright" even though it misses or over-saturates, hiding muchterrestrial detail you need to to see most.

Cyradiance Technology  provides its most light intensity at wavelengths shorter & longer than 555nm, plus a 490-505nm cyan boost. This is the inverse ofother white LED spectra. The OwlSight provides more total visible radiant light than most other LED lamps for a given amount of battery power.

Cyradiance light boosts both the Cyan and Red-to-Deep Red spectral ranges to better "differentiate" colors, textures, and other object surface details.    The Cyan Boost also greatly improves distance-vision when you are dark-adapted & using your eye’s rods, thereby providing excellent mesopic vision using less power, while also enabling superior photopic vision at higher light intensities.

Our objective is to provide power-efficient, precision illumination to maximize the most useful color and detail revealing light reflected back to your eyes from the widest range of natural objects.  New high-efficiency LEDs allows us to output more total radiant light power than the typical LED in the market, so even though more of spectrum is in the reds and deeper blue and violet ranges (plus filling in the cyan gap), these lamps output enough "brightness" to do the job without over-staturating the yellows and hiding detail you want, and need to see.

Having an ability to output more light is good as long as you can scale down to the the correct intensity for the task at hand and outputting light outside the visible spectral range like old incandescent bulbs did can be wasteful of energy, BUT the most important spectral components must be present at sufficient relative intensities for the state of your dark adaptation.

When is "Brightness" Important?

   

Brightness as a metric is best for assessing non-illumination usages such as signaling (e.g. traffic signals, warning lights, or beacons), or when your objective is to shine in the eyes disorient (or just irritate) someone at night for a few seconds. Brightness can be viable for assessing illumination when just looking at high contrast surfaces that reflect a lot of the parts of the spectrum the light source provides, like when looking a black and white text or dry yellow grass next to black rocks using a conventional super-bright cool white LED.

Again, brightness became confused with amount-of-light for most people during the 1920's-to-1980's when almost-all consumer lighting and flashlights were incandescent with similar spectra that contained plenty of red light. If the spectra of two lamps are the same, then brightness can indicate amount-of-light. LEDs are very different from incandescent bulbs and can have very different spectra, even relative to other LEDs. 

If the spectra of different light sources are almost the same, such as most televisions, smart phone screens in all-on-white mode, or comparing same type light bulbs, then brightness can tell you the "relative" amount of light they output. But, only when the spectra are almost the same! 

As discussed, brightness can be increased by either (1) increasing the amount of light, or (2) by changing the spectrum to contain relatively more yellow-green light (less relative violet, indigo, blue, cyan, orange, and reds). Focusing light at the eye or a reflective surface also increases both light intensity per unit area and the apparent brightness at that spot. But, that smaller, brighter spot illuminates a smaller area and can over-saturate parts of the spectrum in the spot, destroying your dark-adaptation, and reducing peripheral vision if pointed at objects up-close. 

 

If your objective is better vision when "illuminating surfaces', you need to know the "radiant light power intensity" and the "relative intensity vs wavelength spectra", along with the "optical characteristics of what you are illuminating".  There is no single "goodness" number for illumination that cannot mislead you when dealing with illumination.

Are Some Parts of the Visible Spectrum  More or Less Important Than Others for Outdoor Illumination?

Spectral importance depends on what you are looking at. Missing seeing one object that trips you up on a 8 hour hike can make for a bad night.

Of the over 15,000 outdoor objects we studied so far, the mid-violet to deep-red light (425-700nm) was most important for providing the greatest power vs visual color & detail benefit !  UVA became important in some situations when greater fluorescence provided a visual advantage. 

Less Important:    Again, Remember that All visible wavelengths can be important!  

While always part the reflected visible light spectra from outdoor objects, UVA-to-mid Violet light (400-425nm) tended to be the least important for outdoor surfaces and hazards. This is because violets were more frequently absorbed by surfaces and that there were plenty of other reflected wavelengths to use to make differential color, pattern, and texture assessments on surfaces we studied.

This UVA to mid-violet spectral range plays roles in our perception of translucent surfaces and coatings like water films, waxes, oils, or ice.  

400-425nm violet light induces fluorescence in some materials, but UVA induced fluorescence always worked better than violet light alone.

Therefore, our Mode 4 illumination contains mostly 425-700nm light with UVA, and a little less 400-425nm violet light for power efficiency.

Less important does not mean "not important".  You still get useful light in this 400-425nm region.

Most important:

Red wavelength light is probably important for most outdoor surfaces based on its frequency of occurrence, intensity, and variation for exposing detail in our many measurements. But, our eye sight is weaker in this spectral range, so it needs to be boosted relative to yellow-green if improved detail perception outdoors is the objective. But just one part of the red spectrum is not adequate. You need all the visible red spectrum the rest of the visible spectrum for accurate vision.  We also boosted cyan 480-510nm because of its importance for differentiating vegetation and for dark-adapted distance night vision.

Above 700nm our eyesight is quite weak, so a great deal of power would be needed to make good use of this region even though it would otherwise be a very important region based on differential reflective characteristics we observed. You get some light even above  730nm in our current illuminators. 680-730nm light is most useful for the blackest soils where all the other wavelengths are absorbed because all these surfaces did still reflect the deeper reds. Even though these surfaces sill appeared black or very dark red, They were at least visible.

Ultra-Black soils were encountered in several  tropical and temperate forests just under the surface debris (most often those that had been burned at one time), and around the openings to a variety of almost-black color animal burrow entrances. 

For an overall "High Quality Light" for illumination, a very broad spectrum with selectable

radiant flux values will work best for the widest range of surface types.

Relatively less light in the yellow-green part of the light spectrum allows your eyes to perceive more detail in most

darker-absorbing natural surfaces even though "brightness in lumens" is lower for a given amount of light power (audio analogy).

Special Color Lights and Filters Used for Illumination

There are a variety of special colored LED lamps and filters in the market. None are like the Nulumina ActiveRed or ActiveV filters,

as we are aware of no other active photonic filters in the headlamp and flashlight markets.

Nulumina's ActiveRed filter: The Nulumina ActiveRed filter super-efficiently converts most of the not-red spectral light into orange plus all visible red light wavelengths, so you get 5-10X the amount of red light relative to any red-filtered white light using the same amount of power.

 

The ActiveRed filter also passes a small amount of light with a carefully shaped broad-spectrum to provide decent color pattern and considerable detail when dark-adapted, plus enough blue and cyan light for your rods to be useful for seeing distances. Red-only light limits you to the range you L-Cone can see, but your rods can add 1000X or more to your visible distance.

Having a proper mostly-red light spectrum for mesopic vision has many uses, allows you to see more around you (along the trail or in your boat, etc..), utilize other dim light sources like a crescent moon or filtered moonlight,  be less attractive to insects, be less visible to nocturnal animals if you are in a blind, and still see any faint lights off in the distance. The only downside to using a mesopic vision optimized spectrum is that it is less forgiving if you look directly at the lamp, so don't look directly at the lamp unless you want to restart your dark adaptation.  The ActieRed filter is only available in the OWLSIGHT Headlamp and the CG2 Flashlight.

LEGLIGHTS have a special version Cyradiance LED for dark-adapted vision that appears almost pink or magenta in color. This LED outputs greatly increased red and deep-red light relative to the rest of the light spectrum. We found this special night-vision LED light to be best for low-power consumption and for optimal mesopic vision when the lamps are located on the legs, closer to the ground surfaces being illuminated. 

Red LEDs only give you about 1/4th the visible red spectrum, so you have a very limited spectral range of even red-reflecting objects you can see well. Red LEDs typically do not cause restart of dark adaption if you glance at them unless they are very intense, but typical ~620nm red LEDs can still cause a dark-adaptation restart if you directly look at powered red LEDs for more than a few seconds.

Nulumina's ActiveV filter:  This filter does not change the spectrum of Cyrandiance LED light, it just widens the beam like widening the focus because of its microlenses (many tiny lenses you need magnification to see are in the filter that increase the light beam width about 3-4X).

When placed over active UVA LEDs, this filter efficiently converts almost all the UVA into broad spectrum Violet-to blue light + some cyan light.  This is a very useful spectrum for many types of objects that are fluorescent in violet light, such as many fungi, lichens, plants, etc... The purpose of this filter originally was as a way to fill out the entire visible violet spectrum for skylight+daylight simulation in Mode 2. However, you can see many surfaces well using this ActiveV filtered UVA light because of the blue and cyan in the spectrum, especially when dark-adapted. We found ActiveV filtered UVA to provide an interesting perspective on the world. Try and see what hidden objects you may discover.

 

Only the OWLSIGHT Headlamp has the full ActiveV filter. The lens of LEGLIGHTS are a partial  ActiveV filter that only converts only about 25% of the UVA light into violet, indigo, blue and cyan light, so you can still see a strong UVA effect, plus just a little more of most everything else.

Yellow LEDs and Yellow filters. Most white LEDs using in headlamps and flashlights output mostly yellow light now, but there is a narrow blue peak that make the light appear white. Yellow light that has almost no blue and little green light can increase the apparent contrast of certain mostly yellow-light reflecting surfaces. There is little reflected light from other wavelengths. Like a great many things, this can be good or bad depending on the situation, but it is seldom good to throw away most of the spectral information your eye-brain system uses to discern detail.

Green LEDs or Green filters, Blue LEDs or Blue filters:  The advantages and issues for "illumination" are similar to that of yellow light, except you are using different parts of the light spectrum, so different narrow type groups of object types can be reasonably observed. There are times this can be useful, especially when used with broad spectrum lighting as a reference. 

 

3b. Vision and sound perception have analogous characteristics.  

Our perception of both sound and light falls off are high or low frequencies (or wavelengths, since these parameters are both effectively parameters of the same wave measurements). 

In Audio, most most audiophile sound systems boost the high and low frequencies in the audible range to reveal more detail in sound. The same is true with light, except you never before had an easy way to make this correction using light. You could change a gamma curve on your TV, but since these are actually just R-G-B pixels, but not continuous all-visible-color wavelength illumination.

In the graphic below you can see how these audio and light sensitivities change with wavelength. Each of the 3 type cones and the rods have their own unique wavelength vs. response spectra. 

Think of the OWLSIGHT Headlamp and LEGLIGHTS As If They Are Amplifiers with "Equalizers" for Light With Very-Useful Presets

Full-spectrum light gives you the entire range, and Cyradiance boosted reds and cyans is analogous to a top quality quality audio system, but for vision.

3c. Multiple Light Sources at Multiple Angles

 

Photographers and movie makers long ago realized the importance of multiple light sources at different angles for bringing out detail. In daylight, you also have multiple light angles due to direct sunlight (sometimes), skylight, and light reflections off nearby surfaces.

Multiple light sources is also important for great vision when night trekking, running, etc... LEGLIGHTS are a great solution for to how to do this. Getting the right intensity, spectrum, and wide angles in a lightweight low power package was a challenge, but we think you will be delighted with the 2 added light angle studio-like effects of LEGLIGHTS when used with a balanced broad-spectrum headlamp, plus having your foot-forward zone continually illuminated so you can be more footsure is a huge benefit on rugged terrain.

 

The graphic below helps visualize the benefits of multiple light sources with full-color spectra and gradual intensity variation lighting. See the USING OUTDOOR LIGHTING section of this website for more information on getting started with mobile studio-like lighting for better vision and being sure-footed at night.

3-Source Cyradiance light can be almost like having morning sunlight at your back "all night long"

Mobile users: Additional content is available on desktop website

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