We have been considering some LED lights for the fire company to replace the Mag-Light lamps that burn out.

After a one-month test, we have gone back to "classic" lamps in the Mag-Lights.

Here's why:

Color Rendition. The "white" LED lamp simply does not accurately render colors. The blueish cast of these lights is not like daylight at all, as it's lacking the color spectrum of the incandescent lamp.

Better LED's just came out:
http://www.ecogeek.org/content/view/1000/

But they are a long way to market.

We'll wait.

How do the LED makers get white without having a spectrum? Do they just combine specific wavelengths in order to get white? Why does a white LED have worse color rendition.

BTW, not all white LED's have a bluish tint.

Yes, it's only the cheapest "white" LEDs that have a decidedly bluish or even purplish tinge. The better makers separate them into color of white, and you pay a lot more for them too...generally this is only done for the LEDs that are more expensive to start with, like 1W+ Luxeon etc.

There are numerous ways to get white, but the most effective one seems to be using very complicated chemical coatings that act as filters.

The cheap "white" LEDs are OK when you just need light, not for pros.

The incandescent lamp does not give a colour spectrum which would be representative of daylight either.



Spectral power distribution output from a Tungsten Halogen Bulb



Spectral power distribution output from a White LED

The light colour from a traditional Mag Light is a very yellow colour and a lot of the energy spectrum is in the infra red, hence the poor visable light emissive efficiency compared to a White LED. Trying to determining accurate colours using either a Tungsten halogen or White LED would be difficult in both cases when compared to natural daylight.

It could be that because the light from the Tungsten halogen bulb has a smoother less variable colour spectrum than the White LED spectrum it could be that interpreting colours by the human eye is less taxing and confusing.

Certainly an interesting observation though. Does everyone at the fire company have the same reservations about the new white LEDs? I suspect they would considering they have all passed the same colour blindness tests.

I have heard of this before, especially from people who use lights for paramedic-type uses. As I understand it, the ability to "see" a person's skin colour tells you a lot about their true condition (blood loss, internal bleeding, etc.). Incandescent lighting apparently makes these changes stand out more than LEDs.

"White" LEDs use a phosphor-type coating to convert blue light to white. It's somewhat like the technology of standard fluorescent lighting. Every type of white LED has a proprietary coating; cheaper usually means more blue-ish, though that's not a hard and fast rule.

(On the other hand, the "cheap blue" LEDs make the eyes of night-time animals light up like a Christmas tree, from great distances, even when the light is very low-powered. Very cool to see two glowing eyeballs pointed at you from the better part of a hundred yards, when all else is darkness.)

Photoplethysmography (PPG) machines used to determine local subcutaneous dermal blood perfusion use the same idea. Its now used in non-invasive blood gas monitoring also i.e. how pink or blue a SCBU baby is, but is a lot more accurate than a visual interpretation. This again works by measuring the back scattered light of infrared lasers from the skin surface. Scanning Laser doppler machines work on the same principle as the PPG machine but work over a larger area of the dermal surface giving a pictorial representation of the blood perfusion of that part of the body. Very useful for determining whether a BK or AK amputation is required due to the viability of the skin flap.

There are a few manufacturers that make LED models specifically for firefighters. Didn't pay too much attention to them, but I think they are picking a specific wavelength to cut through smoke, ie, less backscatter reflection off the smoke.

Look around on candlepowerforums.com and you'll find them.

I'm color blind. I can't tell the difference between a good white LED and incandescent.

You see that MASSIVE BLUE SPIKE? That's the problem - the blue overwhelms everything, and, while a halogen light isn't "daylight" (heck, "daylight" isn't "daylight" - it changes throughout the day, the reality is that the color PERCEPTION (I don't care what color meters say) is very, very wrong with most LED lamps - including the 5W Luxeons we tried, that were specifically designed to prevent backscatter and all that (these were firefighter-specific bulbs).

There are studies about the color perception issue:
http://people.csail.mit.edu/unamay/publications-dir/lro.pdf

Also, terrain visibility is an issue, and this article touches upon it:
http://caves.org.uk/led/led-myths.html#compare

There are numerous articles in here about the "true white" issue:
http://www.ledjournal.com/led_whitepapers.htm

I personally own a lot of LED flashlights, I have tried, several times, to introduce LED lighting into my home, without success because of the horrid color quality of the LED lights.

While I'm on that subject, I only recently was allowed to move Compact Floros out of the basement and into (limited) use in the living areas of the house. Currently, because my wife is very, very sensitive to the color rendition of CFL's, they are banned from the Bedrooms, Bathrooms and KItchen. However, they are now in the hallways, garage and in the living room. We don't use them in any dimmable situations, because the dimmable CFL's are a)terrible and b)expensive

Anyway, I know we all like the LED's here, but I thought it interesting that I was also on the "let's not use these for fire calls" side. We only had 2 members who felt that the LED's were OK for real calls.

Having trouble seeing the number 56

yes, then try adjusting your monitor colour gamma's (red and green). You can do this if you have Adobe Gamma in your computers control panel.

This subject is really interesting. Colour perception is a subjective issue. I myself have supposedly got partial red/green colour blindness. This was determined when I was at primary school when I was tested. I was apparently abnormal when it came to distinguishing red and green colours.

The truth is that I wasn’t abnormal at all, its just that the second rate star 93 million miles away was emitting slightly wrong amounts of red and green light in its colour spectrum.