Blue-green for lowest power?

[cprstn54]

Will a blue-green LED headlamp give you the most usable illumination for the least power?

This would be for use in a tent to read or play cards or on the trail.

I am not concerned with preservation of night vision.

As for torches, wouldn't a green LED let you see much more than any other color for the same power? The literature suggests that you would need one thousandth the power with green than with white to make out the same shapes.

Ken C

 

[DM51]

Welcome to CPF, cprstn54.

I'll move your thread to the Headlamps section.

 

[fyrstormer]

A white high-power LED running on about 50mA will give you plenty of light to read; you might even be able to use less power than that and still get good results. If I had to use a single-color LED, emerald-green would be my first choice, I wouldn't bother with single-color LEDs for long-term use unless I needed to preserve night vision, which you already said you don't.

 

[Ragiska]

1000 times? not sure where you got that number, but it's completely wrong.

since you are not worried about night vision, you seem to be talking about photopic vision, where 555nm light is less than twice as sensitive phosphor white led. for VERY dim scotopic vision, 507nm is still less than 5 times as sensitive as a phosphor white led.

for general purpose, a white led would be far more useful. you could get a white headlamp that could run for weeks or even a month continuously at a low setting.

 

[cprstn54]

See:
http://www.aoa.org/x5352.xml

Well, red would have to be 1,000 times as bright as green to get minimal perception. See "Day Versus Night Vision." No?

I have also found that I can easily read by the light on one 3mm green LED but not a white one.

Ken C

 

[Ragiska]

i don't think you quite understand that article.

long story short, just get a high power WHITE headlamp with a moon mode if all you are concerned with is long battery life.

there are 1xAA headlamps that can run continuously for 22 DAYS. 2xAA for a MONTH.

 

[cprstn54]

I am here seeking knowledge, so it would be helpful to identify what I misunderstand because the article is pretty clear about the 1,000 factor between day and night vision.

As for moon mode, which I assume to be in the range of 0.3 lumens like the H501W provides at low-low, seems to me that if it is using your night vision, it will look blue-green to you anyway and 2/3 of the power will be wasted.

As a practical matter, there is a level of illumination and a mix of colors that optimizes power yet still lets you see enough in the middle 10% of your field of vision -- where there is a deficiency of green rod receptors -- to play gin rummy in your tent. That is what I am looking for. I suspect that this can not be done with rods alone and the power will be something like 1,000 times the minimum needed to make out shapes with your green-sensitive rods.

Ken C

 

[TorchBoy]

The difference between day (photopic, cones) and night (scotopic, rods) vision isn't green vs white light. It's about how much light there is available, whether you want to see colour, how long you're prepared to wait for full sensitivity, and what part of your vision you want to use it in. To read you'll probably want to use the centre of your vision, which is full of colour-sensitive cones. In other words, your photopic vision. Your scotopic night vision can take half an hour to really get going anyway, so it would be impractical if you were going for glow in the dark watch hands for reading with.

Hm, maybe that doesn't really answer your question. White LEDs are more efficient than green LEDs, and will be more pleasant to use. Go with white.

 

[alpg88]

human eye sees green light as the brightest, iirc,
i swapped white leds on one of my cheap loner headlamps to green leds, but i did it, just for originality, not for night vision, or efficiency, not many ppl have green lamp. plus when i loan this lamp, i see where it is.

 

[TorchBoy]

The brightest green XP-E bin is 100 lm @ 350 mA (Q4 bin), for cool white 122 lm @ 350 mA (R3 bin). Like I said, white LEDs are more efficient. http://www.cree.com/products/xlamp_xpe.asp

 

[red02]

it sounds like a good idea for a 5mm LED. I carry a 565nm Photon Freedom, I don't think the white led that came with it was as bright.

I think that idea is explained somewhat here:
http://en.wikipedia.org/wiki/Luminous_efficacy

 

[Apollo Cree]

1) You're misunderstanding the meaning of the 1,000 number. Your rods will react to blue, green, or red light, even though you'll only see it as black and white. The 1,000X figure is for the difference between seeing colors and seeing black and white, not the sensitivity of your rods to white vs. green light.

i.e. "Day vision vs night vision" is not the same as "night vision with a green light vs. night vision with a white light."

2) Even if you're viewing monochromatic night vision with your rods, a monochromatic light source like a monochromatic LED affects your vision adversely. For instance, if you were looking at a playing card, a red LED would tend to obscure the red hearts because the red ink and the background would both reflect the monochromatic red light. If you're trying to see a blue object in the dark, a red LED will not light it up as much as a white LED to your night vision.

3) Blue LED's tend to be more efficient in terms of producing watts of light for watts of electricity in. White LED's are blue LED's with a phosphor, so they tend to be more "efficient" than green LED's, even though your eyes see one watt of green better than one watt of white.

 

[cprstn54]

I think that idea is explained somewhat here:
http://en.wikipedia.org/wiki/Luminous_efficacy

Aha! "Luminous efficiency"!

I think this is what I was looking for. According to this Wiki entry, 555 nanometers (green) is roughly 2.7 times as "efficient" as ideal white, with the computation based on perceived brightness.

So, if longest possible [usable] run time is the prime consideration, a green LED is your best choice.

Thank you.

 

[Apollo Cree]

Aha! "Luminous efficiency"!

I think this is what I was looking for. According to this Wiki entry, 555 nanometers (green) is roughly 2.7 times as "efficient" as ideal white, with the computation based on perceived brightness.

So, if longest possible [usable] run time is the prime consideration, a green LED is your best choice.

Thank you.

Unfortunately, the answer is "no."

Even though your eyes are more sensitive to green light than white light, white LEDs usually produce more light per watt of electrical power.

The "luminous efficiency" you quote is the "LER-Luminous Efficiency of Radiation" in the Wikipedia article you quote. The "efficiency" you care about is "LES-Lumens Efficiency of Source." White LEDs usually have better LER than green LEDs.

This web page shows green LEDs with 80 lumens per electrical watt and white LED's with up to 150 lumens per electrical watt. YMMV.

In practice, white beats green, although you can make an inefficient white LED that's less efficient than a good green.

 

[TorchBoy]

Aha! "Luminous efficiency"!

No, luminous efficacy. The number of lumens per watt that a light source is capable of is what you want to look at.

So, if longest possible [usable] run time is the prime consideration, a green LED is your best choice.

You didn't read my two earlier posts, did you?

 

[Sub_Umbra]

Blue-green (cyan) is great for dim lights if you can find a model you like. I use blue-green lights for most tasks and it performes very well for situations where you want longer runtimes or greater output than white.

While not a headlight, a good example would be to compare an old CMG Infinity Ultra with a white beam to the much lower powered plain CMG Infinity equipped with a blue-green LED. The blue-green Infinity will put out very nearly the same brightness as the white Ultra -- but with two to four times the runtime.

There is a learning curve with any monochromatic light, however. You'll see more the more you practice.

In my experience preservation of dark adapted vision is not much of an issue with cyan. Poor or non-existent 'pointing discipline' is far more a hazard to dark adapted vision than beam color in the real world. It is just a matter of degree. Cyan is just a little easier to make a mistake with, that's all. I have used cyan for preservation of dark adapted vision every night for over four years with excellent results.

 

[TorchBoy]

Blue-green (cyan) ... performes very well for situations where you want longer runtimes or greater output than white.

How will they provide longer run times than white LEDs which are more efficacious? :shakehead

 

[Sub_Umbra]

How will they provide longer run times than white LEDs which are more efficacious? :shakehead

"Efficacious?" For you, perhaps.

I'll give you another example. If you take a Covert Nose Photon Freedom in NV Green (cyan) it may be depowered by replacing it's stock cr2016s with one cr2032. That will cut it's voltage to 3V and change the wavelength a bit -- but it will still be blue-green. It will be dimmer and it will be perfect for close quarter work while maintaining dark adapted vision. It will also run 24/7 for 12 days without getting noticeably dimmer.

I understand that in your situation and perhaps with your Light Culture this setup would not be efficacious for you but that does not preclude it from working well for others. This forum would be quite a bit smaller if we only wrote about lights that emulated what we are all used to -- the floody bright white light from the sun.

 

[TorchBoy]

A bit touchy about light culture there. This thread isn't really about the brightest light, it's about what will "give you the most usable illumination for the least power". The figures I quoted above are examples that show that white LEDs give more lumens per watt than green or cyan LEDs. If you know of a more efficacious green or cyan LED, please post details.

Folk on DX have also talked about halving the battery like that with the white LED Photon knock-offs. So you can have your ultra-dim anti-light culture keyring light with a white LED running on microamps, and it'll still be more efficacious than a green or cyan LED running in a similar configuration. Nice.

As an aside, efficacy (noun)/efficacious (adjective) is lm/W, while efficiency (noun)/efficient (adjective) is percentage. Yes, efficacious is a word.

 

[Sub_Umbra]

...As an aside, efficacy (noun)/efficacious (adjective) is lm/W, while efficiency (noun)/efficient (adjective) is percentage. Yes, efficacious is a word.

You're a little touchy about what I didn't say about efficiency.

While your whole lm/W point is not completely irrelevant to the OP's question it does lead him far down the road in the wrong direction -- lm/W is only one part of the picture when judging the value of different colors for shape recognition acuity. To consider it as the end all and be all is to completely miss the big picture.