Level - 2 Understanding Illumination Spectra and the Reflected Spectra of Outdoor Objects
First: Understanding the metrics and what they mean to you:
MORE DETAIL ABOUT THE DIFFERENCES Some of my graphics
Then, summarized data in a chart (organize data different from SPIE)
The reflected spectra from most natural objects is a poor match with the spectra from today's LED headlamps and flashlights!
Most natural objects tend to be moderate-to-highly metameric, in that the color, color patterns, and visible detail are light spectra dependent.
1a) All The Reds: The "entire" visible red spectrum of light (610nm to 720nm+) is one of the most important spectral ranges reflected that are from almost all natural outdoor surfaces! This range includes orang-red, reds, deep-reds, and borderline near-infrareds. Huge amounts of red reflect from almost every natural brown, gray, black surface, and even the greenest appearing vegetation.
Your light source needs a wide-spectrum of visible red light, Not just a small part of the visible red spectrum from red LEDs. Because your eyes are 10-100+ times less sensitive to red (depending on the red wavelength) than to 555nm yellow-green (the mid-range of visible light), you need boosted red light to see fine details and color variations.
There are several tradeoffs between (1) how similar like objects may appear relative to being viewed in good quality sunlight, (2) maximizing human vision color range and detail perception, and (3) the amount of energy required in the red (or the violet) spectral range(s).
For greater vision color range and detail perception, you want more light intensity at wavelengths (or light frequencies) where your vision is weaker. You can in theory increase the intensity of increasingly longer wavelength red light quite far to compensate for your red-cone vision sensitivity fall off (or take the near-infrared filter off your camera, but keep the color filters in place and look at some images. )
On the red end of the visible light spectrum, most humans can easily see past 800nm near-infrared light at moderate intensities in near darkness (without significant other visible wavelengths in the background). If you attempt really use your vision for maximum detail perception out to 750nm with other colors present. Interestingly there is quite a bit of near-infrared light reflected from most objects, and it does vary with the object type. Like red light, near-infrared covers a huge wavelength range.
There are quite a few different definitions about where Near-IR starts and red ends.
The 1931 CIE chart that defines "lumens" of brightness puts the human limit at about 700nm
Today's white LEDs mostly match the CIE curve for maximum brightness while still appearing white looking "at the light source" or on highly reflective white surfaces. This spectrum is not remotely like sunlight and it does not improve your ability to see details when reds or violets are significantly present in object surface
es relative to any broad spectrum light source such as old hot filament bulbs.
Increasing the light source intensity to compensate for the fall off in red or violet cone sensitivity can greatly increase the effective spectral range of human vision, up to some practical intensity level. Where is this point and what can
These red colors are frequently not percieved because various reds can be easily hidden by colors our eye is 10-100X more brightness-sensitive to such as green or yellow, but red light still effects the appearance of most natural colors. Look at a bruised leaf with internal patterns next to each other, and the internal patterns and stressed part of the leaf are more noticable.
Put 2 similar green objects next to each other and the more-red shade difference becomes visible. Example: a slightly damaged leaf and a undamaged leaf.
Or, boost all the red light in your spectrum to reveal what has been hiding. This is analogous to how an audio studio or hearing aid amplifies high and low frequency sound to reveal more detail. Cyradiance does this with light.
Headlamps and flashlights in the market today provide grossely insufficient red light for almost everything you encounted outdoors
1b) Cyan spectral light (490nm-510nm) also reflects to varying degrees from almost everything you encounter outdoors. It is a differentiator for color in vegetation to help you more quickly determine plant type, and better see plant damage when tracking or when looking for a recently used trail.
Additionally, your eye's rods are most sensitive to cyan light. When you are dark-adapted, cyan light lets you see further using less power because your rods are 100X as sensitive as your eyes color cones.
Remember that "lumens" is a cones-only perception of brightness metric, so your longest distance night vision can be obtained with cyan light for a given amout of total light (radiant flux). Just don't even momentarily look into your lamp or you will loose your dark-adaptation for another 20-30 minutes
LEDs used in other headlights and flashlights provide very-weak cyan light.
This limits your dark-adapted vision and color detail differentiation.
1c) Indigo, violet, and UVA spectral light bring out more colors or fluorescence from many flowers, fungai, scorpions, and fluorescent gear.
On the violet end of the spectrum increasnig the intensity can quickly be uncomfortable if taken too far.
Adding more short visible light wavelengths means having a wider range of light refraction angles in clear thin films and increased differential reflection from many microstructed surfaces. This light can make slippery films, scum patches, black ice, and thorns or nettles easier to recognize.
Reasonably safe 380-400nm UVA light brings out almost all of what you need to see for fluorescent objects plus surface details, and trekking safer.
Just don't sit and stare into the lamp (or into any other lamp), but we suspect have better things to do with your time anyway. A few 1 second glances at most flashlight and headlight LED lamps will provide far less exposure than a split second glance at the sun, but it is best to minimize looking into any lamps to be the most safe, and avoid needing to reset your eye's dark-adaptation timer.
The violet-indigo spectral range is virtually missing from all of today's LED white light headlamps and flashlights.
1d) Yellow and Green light reflects fomr many plants, and from most white or light-colored objects. Your eyes cones are very sensitive to these colors. Even though more red wavelength light is reflected than most oler colors, even a small amount of yellow light cam make an object visible, but without much detail.
Yellow light is important for many objects, but it needs to be lower in intensity than the red or blue-violet wavelengths for your best overall visual acuity.
A spectrum with higher relative red and blue-violet light power than green and yellow is also a common characteristic of great morning sunlight.
Put morning sunlight spectrum and Reference spectra here
The Illumination and Refected Spectra Mismatch
There are three (3) huge spectral weaknesses in the spectra of LED headlamps and flashlights you are using today! Half your visible spectral range is seriously impared using even the "brightess" headlamps or flashlights.
These gaps are the Red, Cyan, and Indigo-to-Violet spectral ranges. These happen to be in some of the most important spectral ranges.
Remember that these are large spectral ranges, so "Red", "Cyan" or "Violet" are not a single colors. They aqre coninuum of color we categoried for simplicity. Each wavelength can interact with other wavelengths and reveal different information about various objects.
For example, visible red light wavelengths range from differently 610nm (orange) to over 720nm deep-red. Most human eyes can see up to 800nm, but we selected 720nm because
"Amount of Total Light" is correctly measured in "Watts" of "Radiant Flux", NOT "Lumens" of "Brightness"
You want the right amount of light for a situation. Brightness is also important, but it is not the most important parameter for outdoor portable lighting.
Too little light and you feel uncomfortable. The amount of light you need depends on your level of your eye's cone and rod dark-adaptation.
For over 50% of your rods to be active, typically takes at least for 20-30 minutes in near-darkness or red light (or our ActiveRed filtered mesopic night vision light) until you become mostly dark-adapted. The time required to become dark-adapted depends on the characteristics of your personal vision, your environments lighting, and how much intense light you were exposed to during the day (especially in the 1-2 hours before you start dark-adaptation). Even very high intensity red -only light can delay dark adaption.
Too much light (like mid-afternoon summer sun) and you reach for the sunglasses. Some colors saturate and some colors wash out as they are overwhelmed by reflected yellow green light or background light. Also, any spectral color of light starts to appear white as the radiant flux at that wavelength gets very high.
Since you also do not want lug huge stockpiles of batteries around, you want the right amount of light so see everythg you really want to see.
But, you do want the "option" of going to a high radiant flux if needed, so you want the capability of outputing a lot of light.
A high brightess spectra is OK for reading a black and white newspapers, but walk outdoors and half what you want to see fades under the glare of reflected white-appearing light dominated by mid-green to yellow light, or just goes gray.
The highest brightness in "lumens" for any power level only requires mostly yellow-green light, and just enough red and blue light to appear white. Do you want to blind people, or see more?
A little more detail about "Brightness" vs "Amount of light"
Just to help make your article technically correct, lumens and brightness are not measures of the "amount of light" from a lamp, although very few people know this fact.
The amount of light emitted from any lamp is actually measured in Watts of radiant flux.
Lumens is calculated from the measured amount of radiant flux "amount of light" based on the 1931 CIE eye sensitivity vs light wavelength curve looking directly at light sources. This 1931 study has since been shown to be flawed and the CIE has issued several correctionts, but old standards tend to be difficult to update so the 1931 standard is still used for "lumens".
Also, if you are dark adapted then lumens become even more incorrect because lumens only applys to vision with all or almost all the eye's rods turned off. Since the human eye's rods are 100X more light sensitive than color cones, and you have 20X as many rods, ignoring rods and their special cyan sensitive is not such a good idea for hilkers and other outdoors people.
In 1931, almost all lamps were hot filaments (black body radiators) emitting similar light spectra, so you could use lumens to compare the amount of light. LED are not black body radiators and their spectra can be very different from each other, therefore many long-established terms can be very incorrect when used with LEDs. Filiment lights wasted a lot of energy as heat and were not very reliable, but the were continuous broad smooth spectrum lights. LEDs can be very narrow spectrum and have gaps, and most white LEDs do have some
There are two ways to make a lamp's overall output "brighter". These are (1) increase the "amount of light" or radiant flux, and/or (2) change the spectrum to mostly yellow-green light where the eye's cones percieves the highest brightness.
A white-appearing light spectra with mostly yellow-green light is called "super-bright". These LED spectra usually contain a narrow mid-blue spectral peak from a blue LED , and mid-green to yellow spectral peak from most of blue light that was converted to yellow-green spectral light by a phosphor. The yellow phosphors thar are commonly used output only a tiny bit of red light, and leave a gap in the cyan spectral region.
The down side with using mostly yellow and yellow-green (540-590nm) to increase brightness, is that this can be done in a white LED light by minimizing over half the visible spectrum. And this is exactly what is almost always done. Little or no light at any wavelength makes those colors gray away, changing the visible color, hiding patterns and detail, and even making dew and other transparent films more difficult to see.
Unfortunately, other manufacturers of headlamps and flashlights only give you "lumens" of light output in the specification sheet. However, lumens is not the "amount of light". Lumens is the perception of "brightness". The most "brightness" in "lumens" is obtained at lowest cost for any power use by outputing mostly yellow-green light with as little red light as possible.
Using brightness was a small issue in 1931 when the standard of "lumens" came about because incandescent bulbs ruled the market and they all had similar spectra. LEDs are not black ody radiators, so the metrics for color temperature and brightness can lead you to make poor lighting choices when using LEDs.
As previously stated there are multiple factors that can effect day or night vision, organized in a slightly different way.
The top 4 items in this list are significantly addressed by Nulumina's headlight, LegLight, and handheld torch systems.
The lower 5 items may be improved by the proper use of Nulumina Lighting, but also fall into broader categories.
8+ Important Parameters That Interact to Effect Vision Outdoors at Night
1. The Amount of Light (Watts of radiant flux, NOT lumens) and the light spectra
a) Illuminating light's interaction with the objects being illuminated (reflection, fluorescence)
2. Human eyesight interacting with light, such as the degree you are dark-adapted and periperal vision effects
3. Angles of Light Onto Objects and Background/Ambient Lighting
4. Characteristics of the objects being illuminated,
5. Your brain's interpretation of images, reference images, light, motion, attention, memory and recognition of images, responses to visual cues, and situational objectives.
a) The medium (usually air) between you and the objects being viewed will be effected by fog, dust, precipitation, and windows, but can sometimes be partly mitigated by proper use of these illuminators. e.g., in dust, a "mostly" red spectrum light such as an Owlsight Mode 3 with Activered filter can provide better situational vision than a typical white appearing light.
6. The effects of your light source(s) and other light sources directly on you, those near you, and other objects in the vicinity.
7. Your personal vision advantages or vision imparements
8. Optical parameters such as variable refraction, dispersion, interferrence, polarization, and more can all add complexity to visual images
See the Vision Science section of this website for an analogy of how a well designed spectrum of lightng is similar to how high-quality audio systems and hearing aids that boost high and low frequencies bring out more detail in sound and recordings.
CAN A LIGHT SPECTRUM BE BETTER THAN SUNLIGHT?
Sunlight is Great! For a great many vision-related tasks, a sunlight-like spectrum is best (other than removing the potentially hazardous part of the UV and most of the infrared that would waste energy as heat. Think sunlight at your back. Our eye's are well adapted to work with this spectrum and we like it. This is the type of Full-and-Continuous light spectrum that most of our perceptions of color are based on. The Color Rendering Index (CRI) Ra of sunlight is 100, so it reproduces almost all colors well (there are other versions of CRI and there are color gamut values, but sunnlight is always a great color reference standard for illumination.
Show 3 sunlight reference spectra
Natural Outdoor Sunlight also provides many illumination angles due to scattering in the sky and light reflecting off objects all around us. The spectrum and mutiple angles of light are great. Another feature outdoors is that any open area is usually illuminated, so you can see objects very far in the distance (atmospheric conditions permitting).
Shortly after sunrise to mid-morning on a clear day in open terrian tends to be best for vision mostly because the atmosphere is frequently has less dust or pollen, the light intensity is frequently not too high yet, and the primary light angle from the sun provides favorable differentiation relative to the scattered light from the sky.
Sunlight intensity can quickly become too high, and you need to put on your sunglasses. If you are simulating sunlight, that would waste resources unless your object is to blind people. Painful light exposure is easy to do to people that are even 10% dark-adapted.
So, it might seem that just duplicating the spectra of sunlight the extent technology and economics allow would be best, provided you also brought light in from more than 1 source...........................................
and this was Nulumina's first thought.