Blue LED Safety

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RonM

RonM

Flashlight Enthusiast
Joined
Nov 10, 2000
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NJ, USA
This post isn't about potential eye damage from blue LEDs (I know they can really bother my eyes). It's about using a blue LED flaslight for walking or running at night.

Was driving along on a dark wintery night when an unusal blue light caught my attention. Turned out to be a woman walking along using a blue LED flashlight. What struck me is that it caught my attention from a long way away. White lights might be better to see with, but as we drive there may hundreds of different white lights in our field of view at a time. The blue flashlight stood out from all the "white noise" providing the woman with a much higher degree of safety from passing cars, IMHO.

I think this blue LED hater has finally found a reason to warm up to these unique light sources. /ubbthreads/images/graemlins/thumbsup.gif
 
After I read this, I was thinking a Red light would also be effective, but I think you are right that Blue light is more visible, especially from a distance, because it has more energy.
 
Actually, i believe that red light travels farther than any other wavelength. This is why signals are red and so are brake lights.

I could be totally off-base though /ubbthreads/images/graemlins/ohgeez.gif
 
Actually, the Eye is not very sensitive to "Blue"
Here is a chart done on the relative sensitivity of light to an "average" human eye

nm Eye Sensitivity Color
420.00 0.02 Violet
442.00 0.04 Violet-Blue
450.00 0.05 Blue
457.90 0.06 Blue
488.00 0.19 Green-Blue
500.00 0.32 Blue-Green
514.00 0.59 Green
532.00 0.89 Green
543.50 0.97 Green
550.00 1.00 Yellow-Green
555.00 1.00 Yellow-Green
568.00 0.96 Yellow-Green
580.00 0.87 Yellow
594.10 0.71 Orange-Yellow
600.00 0.63 Orange
611.90 0.48 Red-Orange
632.80 0.24 Orange-Red
635.00 0.22 Orange-Red
647.10 0.13 Red
650.00 0.11 Red
660.00 0.06 Red
670.00 0.03 Deeper RED
680.00 0.02 Deep RED

You will see that it "peaks" at Yellow-Green
 
I see that some of those nanometer figures are laser wavelengths. /ubbthreads/images/graemlins/wink.gif

I recognise 457.90nm, 488nm, and 514nm as argon ion laser lines, 532nm as a frequency-doubled DPSS laser line, 543.5nm, 594.10nmm, 611.90nm, and 632.80nm as HeNe laser lines, 647.10nm as a krypton ion laser line, and 635nm, 650nm, and 670nm as diode laser lines. /ubbthreads/images/graemlins/grin.gif

I'm glad I wasn't part of that experiment...having laser radiation shot into my eyes is not very appealing. /ubbthreads/images/graemlins/icon15.gif :toliet: /ubbthreads/images/graemlins/icon15.gif
 
How do you interpret those sensitivity figures?
Is it saying that 10 lumens of Yellow-Green is as easy to see from 500 yards as 100 lumens of Blue?
 
It is also about the environment. Blue is not the best choice from a scientific viewpoint. I can remember being outside a particular mall at night. There was one sign which used glowing blue letters on a black background. The while thing felt "slippery to the eye" for lack of a better term. I could see a similar-sized sign from a much further distance in red and white, but the blue sign was hard to read and hard to make out the edges. Strange.

But blue is good because you do not see it often. You see red, green, yellow, and white lights ALL THE TIME. You do not see blue very often. That makes it stand out.
 
[ QUOTE ]
IlluminatingBikr said:
Is cyan/turquiose somewhere in the 550nm range?

[/ QUOTE ]
Cyan/turquoise is in the 490nm-510nm range. Shorter than 495nm and the light starts to look blue, and longer than 505nm and the light starts to look green.

550nm is a slightly yellowish shade of green. It's only 6.5nm longer than the beam from a green HeNe laser, if you've ever seen one of those things.
I have a green HeNe laser, though it only puts out 10-12 microwatts now and is about to kick the bucket.
Let's see if I can dredge up a picture...

hene2.jpg


Ahhh, there it is. With beam, of course. /ubbthreads/images/graemlins/smile.gif
The green color you see is fairly accurate, though perhaps with just slightly more of a yellowish tinge.
 
Police car lights are blue, I'm sure they must have made studies and decided that they are a better attention getter.

Possibly because they are not the typical colors that you see while driving [Red, Green, Yellow, and White].
 
Exactly OCD. The point isn't that blue travels further or that the eye is more sensitive to it. It's that it STANDS OUT from all the other more common light colors in our world. Most lights are white. Followed probably by red, due to all the car tail lights. A deep blue light bobbing along is a distinct and unusual sight.
 
I agree it's not how far it travels, but what stand out. But that said, red light is longer wavelenth, lower frequency. Think of bass, long wavelengths, low freq. Bass travels a long time. You can hear a car booming from a long ways off. Now think of blue light. Short wavelength, high freq. Lots of engery to excite things but it disapates easier.
Anyways, "lighter" blue's that seem like they have white added to them, that seem brighter or less deep dark blue, like plain blue luxeon (not royal blue) Would work probably the best. that or a TRUE colored cyan. Probably a <font color="cyan">TRUE</font> cyan would get my attention first, because I'd be like whats that weird color? Even more rare than blue..

A straight green luxeon would catch your eyes too since it wouldn't be a traffic light up high, but bobing around on the ground... Plus it wouldn't be the blueish green traffic lights are, but a more towards lime yellowgreen...
 
Don't forget that we're not talking about relative sensitivity here. Those values come from projecting one color at intensity A and then another at intensity B and then adjusting the intensity of one of the colors so that the subjects says 'they are equally *bright*'. That's great for good old Mr. Maxwell (you know, the guy who did the vector field EE equations and who was the first scientists to look into human perception of color *quantitatively*), but they have nothing to do with detection threshold.

The visibility of blue light comes from two things:
1) physical properties. Regardless of how dim or bright a human viewer perceives blue vs other colors, each blue photon has more energy than one of those other colors. Due to how rods and cones in our corneas detect photons, that is a win for blue light. Fewer photons of blue will 'trigger' a rod or cone than an equal quantity of photons of some less energetic wavelength.
2) What RonM was getting at. Due to the lack of other objects of that color, a blue light will stick out when viewed in that context.

These two reasons are synergistic, as well. If you are more likely to notice a dim blue light and there are fewer of them...

Harrkev was right in his(?) observation that blue signs may not be a great idea for night viewing. At night, the pupil is way open and the depth of field of the human eye is at its worst. This ties in to the property of simple lenses--like the cornea--to have different focal lengths for different colors of light. The property is called chromatic aberations. This is exactly what happens in a prisim. Generally, it's an unwanted property in a lens. Complex lenses made of multiple materials--each with a different index of refraction--can be made to have some arbitrary level of aberation. But, simple lenses like the cornea or glasses show the property--more so at the sides than at the center. Look at the sign in your peripherial vision and it'll go *way* shifted.

So, if all the other things out at night are of yellow/green colors, then that is where the eye will automatically focus. If a blue sign gets thrown into the middle of this, it will not focus the same as the majority of the other objects and it will look fuzzy or 'slippery'. It'll be especially bad if the general tone of things is redder. Say, a parking lot lit with sodium lights and a lone blue sign.

So, to be noticed, blue is great at night. But, to *see*, you'll want to keep your light in the yellow/green/cyan range. Especially if you're on a path in the wilderness as the blue light will not illuminate the leaves worth a darn and you'll end up walking into a tree branch or something. /ubbthreads/images/graemlins/frown.gif Oh, red is equally bad for that, too. The ideal color for walking in the forest at night is IR. Leaves reflect it *very* well.
 
My observation is that if you are in a dark room at night and you turn on a 1 watt Luxeon blue light, or white light, people outside will notice that light much easier than if you turn on a red light.

Isaac, I was thinking the same thing about *bass is the same as red*, but red doesn't seem to travel through cracks as well as blue or white. I think red is more "readily" absorbed (no pun intended).
 
Wilmore, are you serious? IR? If red is bad at night, but IR reflects off leaves? What color is it converted to then? Or are you talking about using NV goggles?

Sounds interesting. If it does refeclt a visable color, I might have to build me an IR torch.... hmm. I love stuff like UV/IR that reflects visable colors depending on the surface material..
 
Willmore, excellent post. Your explanation is right on. The blue in the pedestrian's flashlight was both very deep and dark while at the same time seeming "bright". Lighter colors of blue, like cyan, don't seem to exhibit this strange phenomenon.
 
I used a blue everled in a 2D light while trick or treating with my 5 year old this past Halloween. So many, many complete strangers commented on it as we walked along, and told me how cool it was and that they were wondering what it was from the other end of the street! And a quick flash of it at an oncoming car guaranteed we were not only seen, but differentiated from all the other lights/decorations, etc. It truly stood out like a sore thumb. People also commented on how bright it was. It is a very bright LS (got lucky), but it is amplified in perception because people stare at it instead of glance. Think, "moths".
 
Originally Police lights were RED, but they found out that most people didn't accept them as "different" from all the other RED lights on cars, etc - so they set a law saying that ONLY Police cars can have Blue lights

There were some aftermarket tail lights being made for Model-A and Model-T cars that had a small blue dot in the center of the light as a "novelty"; according to the law - even that is considered illegal
 
I spent the last year in Europe, and noticed a small number of vehicles over there have double 10mm blue LEDs mounted on their dashboard shining out. Sometimes at the back as well.

I assume they are for visibility, and they catch your eye, even if the headlights are on. Otherwise, maybe they are just to look pretty. I'm not sure. Most of the vehicles that have them though are trucks.
 
[ QUOTE ]
INRETECH said:
Originally Police lights were RED, but they found out that most people didn't accept them as "different" from all the other RED lights on cars, etc - so they set a law saying that ONLY Police cars can have Blue lights

[/ QUOTE ]
A couple of years back, I got ticketed for having blue LEDs in the front of my electric wheelchair. /ubbthreads/images/graemlins/frown.gif
The magistrate threw the charges out though, as he thought they were silly and frivilous. Still, having a blue light on the front of *any* vehicle is probably a no-no. Whether that is a truck, a car, a bicycle, or in my case, a wheelchair.

Having a blue LED flashlight as a pedestrian is probably OK though, unless the officer driving by and seeing it is a {vulgar term for having intercourse} {vulgar term for anal opening}.
 
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