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sumguy 11-15-07 10:16 AM

can't find
 
I saw a post mentioning some sort headlamp or helmet light with optional green lighting and how it enhances night vision but may be illegal because green may be reserved for civil volunteer workers; can't seem to find it anywhere. have wasted a lot of time. can anyone help?

jeff-o 11-15-07 11:04 AM

There's a whole DIY-instructable on instructables.com. However, the reasoning for doing this is flawed. The theory is that because the human eye is most responsive in the green-cyan range, it follows that a green-cyan headlight would illuminate an area more efficiently. The downside is that it will totally shut off your night vision.

Your eye automatically switches from day vision to night vision when the light levels drop below a certain threshold. They are most sensitive to green light, and least sensitive to red light. Therefore, it takes less green light than red, to switch back to day mode. Using a green headlight will effectively keep your eyes in day mode all the time, severely reducing your ability to see anything other than what's illuminated by the light.

This is also why astronomers use red lights to see by, the red light allows them to see but their eyes don't switch over to day mode which would impair their ability to look at the stars.


In short: Don't build a green headlight.

jsharr 11-15-07 11:20 AM

I have, but do not use a Sigma Sport computer light. I found it to be next to useless. It gives off greenish light.
Maybe this thread explains why I do not like it.

http://i144.photobucket.com/albums/r...harr/sigma.jpg

Chris_F 11-15-07 11:53 AM

Quote:

Originally Posted by jeff-o (Post 5638229)
However, the reasoning for doing this is flawed. The theory is that because the human eye is most responsive in the green-cyan range, it follows that a green-cyan headlight would illuminate an area more efficiently. The downside is that it will totally shut off your night vision.

Any light that produces enough to see by will shut off the night vision, red or green. The advantage of green is it takes less LUX to see by and therefore your pupils remain as dialated as possible. As soon as you turn on any meaningful light your night vision is toast anyway, might as well work to keep that iris as open as possible.

(also, lots of astronomers are switching to green lighting).

As for legality, in New Hampshire I can use a green or yellow light on a road going vehicle but I MUST use a white light. So if you have a green light you need to add a white light. This is different from blue, which is a definate no-no since that's reserved for police. But it's no matter since every cyclist I see breaks the law anyways. Around here it's illegal to use a flashing rear tail light (though it isn't enforced with bicycles).

jeff-o 11-15-07 12:22 PM

Quote:

Originally Posted by Chris_F (Post 5638549)
Any light that produces enough to see by will shut off the night vision, red or green. The advantage of green is it takes less LUX to see by and therefore your pupils remain as dialated as possible. As soon as you turn on any meaningful light your night vision is toast anyway, might as well work to keep that iris as open as possible.

It's true that any light of sufficient brightness will kill your night vision. It's just that a green light will do it faster.

Now, you might ask, "Isn't white light made up of all the colours, including green? Won't that toast my night vision, too?"

Yes, it will. So will the headlights from every oncoming car. So why bother building a light that's only green, when you can make a white one instead?

Sir Bikesalot 11-15-07 01:06 PM

Quote:

Originally Posted by jeff-o (Post 5638796)
It's true that any light of sufficient brightness will kill your night vision. It's just that a green light will do it faster.

I've found that blue light kills my night vision fastest. For maxiumum visibility at night, I'd suggest a yellow/amber light, as that is essentially white minus blue. Of the commercially available lights, halogen comes the closest to this ideal; HIDs are the worst but throw out so much light that you don't need night vision anymore (LED is similar).

Chris_F 11-15-07 01:27 PM

Quote:

Originally Posted by jeff-o (Post 5638796)
Yes, it will. So will the headlights from every oncoming car. So why bother building a light that's only green, when you can make a white one instead?

There I agree with you. If you have a white light there's no sense in putting a green filter on it. All you're doing is taking lumens out. The only color filter I'd consider putting on a light is yellow since that at least improves contrast a bit.

jeff-o 11-15-07 01:55 PM

Quote:

Originally Posted by Chris_F (Post 5639148)
There I agree with you. If you have a white light there's no sense in putting a green filter on it. All you're doing is taking lumens out. The only color filter I'd consider putting on a light is yellow since that at least improves contrast a bit.

Yep. Though the instructions I mentioned before used a cyan LED emitter, so it's pure light in one narrow spectrum.

Chris_F 11-15-07 07:15 PM

Quote:

Originally Posted by jeff-o (Post 5639350)
Yep. Though the instructions I mentioned before used a cyan LED emitter, so it's pure light in one narrow spectrum.

I've heard there's greater lumen/watt potential from colored LEDs than from white, which makes sense since white LEDs are basically UV LEDs covered in phosphorus, so I'm sure there's more loss there. So, I can see why a colored LED would be attractive. But why would they pick cyan? Sure the eye is sensitive to it, but all the "stuff" you'd want to see from a bike isn't cyan colored. It's yellow lines on the road and tan colored sand, or tan colored rock, dirt, leaves, etc off road. I'd think a yellow LED would be better just because it'll catch more "stuff" that'll reflect more of it.

If colored LEDs do get more lumens/watt then it'd be nice to see a light with a red, green, cyan light. May not get nearly "white" light out of it (since the color is so narrow in spectrum) but it'd do a decent job.

timothy002 11-15-07 07:47 PM

www.performancebike.com always have some


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