Why the colored leds?

folsom

folsom

Joined
Oct 23, 2000
Messages
346
I was looking through this forum for a suggestion on a new flashlight, and ended up with both a Inova X1 and X5. I noticed that these and other led flashlights are available in colored leds like red, blue, and green as well as white light.

I can understand the red to preserve night vision, but what purposes do the green and blue serve? Why would someone choose one of those?
 
Blue is supposed to make a blood trail show up better. I have no idea if green has any special purpose.

Paul
 
Green LEDs dont interfere with Night Vision equipment. Your eyes are also pretty sensitive to the green wavelength, so if colour reproduction isnt an issue, a green LED light is more efficient than a white LED light.
For a more in-depth analasys by someone with more knowledge than i, have a look at the following write up:
QuickBeams' coloured light guide
 
Leds defined as white are really a combination for colors that appear white. The blue and green have a slight edge in light output but we prefer the white for closest color rendition at night.
 
Blue is more for being seen than to see with.
It stands out much more to the eye at night.
Even in the day, blue stands out more.
Kinda like a safety warning.
Gotta admit that the blue Photons are cool as hell!
Lenny
 
Although red is great for minimizing impact to your natural night-vision, it can obscure map details, which often have roads or other features marked in red.

Blue is most often used by hunters to pick up blood trails, however, it is also useful as a safety marker. Be aware, though, although more "noticeable" due to its distinct color, it does not necessarily put out more light.

Green LEDs can be compatible with certain night-vision equipment, but its use is somewhat self-defeating -- per the reasoning why would you use a visible light if you have a night vision device, which can take advantage of IR illumination. :)

Allen
aka DumboRAT
 
White of course is the traditional color, and probably the best for non-specialized needs.

I started using blue and green LEDs for several reasons. First of all, both blue and green LEDs preserve night vision to some extent. They also draw less attention to your position if that is a consideration.

Red is probably the best for preserving night vision, but the BIG drawback is that red LED light washes out some critical components of certain maps that I use. You don't want to miss a warning that is printed in red, because your red LED completely obliterated it. Warnings are not generally not printed in green or blue, so as a general safety rule, I simply quite using red LEDs.
 
I never did like LED lights... Even the white color is really some sort of bastardization of blue. I prefer the dull yellowish color of a krypton bulb. I carry a spare since krypton goes every once is a while (as does LED's except there's no way of replacing them) and a few extra batteries.
 
Colin Thompson said:
For the motorheads, blue is also handy for finding coolant leaks.
Click to expand...

:)

Cool, didn't know that ! Thanks a bunch for that tip !

------

MelancholyMutt

You owe it to yourself to try and experience some of the high-end LEDs that are available today -- they may very well serve to change your mind, as many produce a truly "white" light.

Also, depending on the "binning" of the emitter, there is the possibility of tailoring the LEDs output to your particular taste. I actually own a custom-made LED light whose output is slightly "warm yellow" and well simulates that of a traditional incandescent light.

The advantages towards switching to LEDs really is endless, including currently higher-output for longer durations (although absolute output is still the realm of incandescents at this particular time, this is due to change in the near future as LED technology continues to out-pace incandescents), and is in a setup which is much, much more durable with regard to shock resistance.

:)

Allen
aka DumboRAT
 
There are 2 ways of making white light with an LED. One way, sort of like our computer monitors, produces 3 individual colors to activate all 3 sets of cone cells in our eyes to look like white light. This can be done with 3 "indepentant" LED emitters in the LED. The other way to produce "white" light with an LED is more like a fluorescent tube.

Incandescant lights (just for comparrison) heat a filament hot enough that it emits light that will vary in "whiteness" depending on the temperature of the filament. (and throw away 90% of the energy as heat) Fluorescent tubes all produce one "color", ultraviolet. There is an arc running down the tube producing mostly ultraviolet or UV. This UV is absorbed by the coating of phosphors on the inside surface of the tube. These phosphors convert the high energy ultraviolet photons to lower energy photons in the visible spectrum. The rest of the UV is hopefully blocked by the glass tube itself. (this is why you can hurt your eyes or even get a sunburn with an old tube showing black on the ends where the phosphores have been burned off that will let through much more UV). The whiteness of the fluorescent light is dependant on the type and quality of the phosphor, whether it is warm white (yellowish), cool white (blueish), grow light (lets more UV through, concentrates on the blue and red, skimps on the green), daylight or whatever.

"Modern" white LEDs are actually a blue LED with a phosphor coating that will absorb and convert most, a bit over half, of the blue photons and emit lower energy photons in the other colors in the red to almost green range. They usually leave a gap in green, but this is usually not a problem.
 
Colin Thompson said:
For the motorheads, blue is also handy for finding coolant leaks.
Click to expand...

Yep, blue is excellent fo rlooking under the hood at night in general. Details stick out really well. I've always thought the blue was horrible for night vision though.
 
green - when it is actually the spectrum of green, is also good for not interfearing with plant cycles. when gardnening while your plants require complete darkness for certain periods of time *tropical plants or roses that would ordinarily never grow in your climate etc*, having light at all will change how they grow, green however does nothing to them, as they cant see/feed off it
 
Dont the batteries last longer with some colors than others?
 
i was told that the photon 2 whites last 12 hours, and the photon 2 reds last 120 hours.

wether that is true or not, i dont have a clue. the reds take 1 large battery. the whites take 2 mediums, the whites definitely seem to fade faster then reds.
 
shootist16 said:
Dont the batteries last longer with some colors than others?
Click to expand...
Red should last longer than other colors because of its wavelength properties and according to another forum member, is the reason that Victorinox uses red LEDs in their knives with lights (keep a minimum (sp? confused at the moment) amount of batteries for space reasons).

Sorry if I confuse anyone with all the "(()())())((()" :o
 
The different colors of LED have different voltage drops. No matter what bettery and what LED you have, eventually the LED will light dimmer and dimmer, and then not at all because the battery voltage will fall below the point where the LED will be able to light up. For any one battery set up, the higher the forward voltage of the LED, the lower the current draw, the slower the LED will draw current, but the LED may not be able to use all of the batteries total capacity before the battery voltage falls below the minimum forward voltage of that LED. For comparrison, here are the nominal forward voltages of common colors of LED, the voltage and amp hours of common batteries, and some calculations of run times.

Here is one company's Color Chart, other companies use different chemistry for specific colors and so have different voltages. The photon2 bright green is a higher voltage than this chart's for example. Average voltages are probably:
infrared = 1.5V
red = 1.7V
brightred = 1.9V
orange = 2.0V
yellow = 2.1V
green = 2.1V
brightgreen, aqua = 3.6V
white = 3.6V
blue = 3.6V
UV 430nM = 4.6V

Photon single battery is a CR2032 which is a 3V Lithium with 200mAh capacity.
Photon double battery is CR2016 which is also 3V Li but with only 80mAh, so the capacity of the pair is 6V at 80mAh.

So a white that lasts 10 hours on an 80mAh battery has to average somewhere around 8mA. The start current is rather higher and it tapers off over that time. These white LEDs can operate up to about 30mA, and will operate down to a small fraction of a mA for a very dim but uncredibly long lived light. I ran one on a pair of AA batteries for 2 years before it cast absolutely no light. Of course this means the forward voltage is actually rather less than the nominal 3.6V and not all white LEDs will actually do this. The Data Sheet for Panasonic 2016 shows that for 2mA the voltage per cell is only about 2.7V and falling fast. At the needed 8mA it must down to the nominal 1.8V meaning that a majority of power in the white photon light's batteries goes to heat inside the cells, not to the LED.

A red LED on a single CR2032 has 200mA to work with, but only about 1 volt to drop across the cell's internal resistance. At 2+ mA the 2032 cell is down to 2.7V and falling fast. I assume before it reaches 5mA it will be down to the LEDs nominal voltage. The yellow and green will reach nominal voltage of 2.1V at a lower current draw than the 1.7V red meaning the single cell greens last the longest.
 
Green LEDs can be compatible with certain night-vision equipment, but its use is somewhat self-defeating -- per the reasoning why would you use a visible light if you have a night vision device, which can take advantage of IR illumination.
Click to expand...

Aboard a ship.

The night lookouts on ocean-going ships often use night vision equipment to watch for debris in the water, small craft, etc, all of which does not often appear well on radar.

If a deck hand has to go out and check or work on some piece of equipment, and he uses a white flashlight, he can blind the night vision equipment. Modern NV equipment has features to prevent permanent damage, but it can still take a good fraction of an hour for the NV equipment to fully recover.
 
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