ARC LS colors

Hi All,

The cyan LS is supposed to be higher in lumens and candle power compared to the white LS. Would this also mean that the cyan would travel a further distance then white if both are compared in a foggy or smoky environment ?

thanks,

sylvestor

Shorter wavelength light tends to scatter in fog and smoke, making blue, cyan, and white LEDs less than optimal.

Red light penetrates well, but at night the eye is not as sensitive to red as it is during the day. In fact, under red light the eye's pupil doesn't even constrict.

Amber is most optimal, since it has the best combination of relatively long wavelength (for penetration), some pupil dilation (why are amber sunglasses so bright?) and it's a more sensitive color to the retina.

Notwithstanding what I said above, the cyan definitely appears much brighter than the amber under normal atmospheric conditions and driven at the same current.

This is probably due to the human eye's increased sensitivity toward green and blue.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
Red light penetrates well, but at night the eye is not as sensitive to red as it is during the day. In fact, under red light the eye's pupil doesn't even constrict.<HR></BLOCKQUOTE>

Of course it will! If you use, let's say, two LEDs, one red and one blue with the same (scotopic) 'Candela rating' they will have the same effect on your eye's pupil.

And the shift to scotopic view (night vision) is at much lower illuminance levels as most people think.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
the cyan definitely appears much brighter than the amber under normal atmospheric conditions and driven at the same current.

This is probably due to the human eye's increased sensitivity toward green and blue.<HR></BLOCKQUOTE>

If you have two Luxeon LEDs of the same development state (both low dome), the cyan and the amber one have the same brightness (but not necessarly the same radiant flux). If you have two light sources with the same 'candela rating', they are equally bright.
Actually at photopic vision, the eye is more sensitive for the Luxeon's amber than for the cyan.

And how effective your light is, depends very much on your application. We can see this very often in a cave. Sometimes the carbide light is better for viewing something and in other occasions, the LED light is.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Of course it will! If you use, let's say, two LEDs, one red and one blue with the same (scotopic) 'Candela rating' they will have the same effect on your eye's pupil. <HR></BLOCKQUOTE>

It's absurd to use "scotopic" and LED in the same sentence, as direct LED light, regardless of color, is more than intense enough to trigger a photopic pupilary response.

The fact is, at night---and we're talking low-level, reflected light here---the eye is much less sensitive to red than it is to blue/green, and the pupils respond accordingly.

A mountain biker using a bright red LED to light up his path will have larger pupils than one using a bright cyan LED, simply because the eye perceives less light.

Still, from experience, I find the path "easier to see" under cyan light than red or even amber. The best design would probably combine both---cyan for the high beam, and amber for the low beam. That way, distant obstacles can be detected, and closer objects can be more easily scrutinized.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Red light penetrates well, but at night the eye is not as sensitive to red as it is during the day. In fact, under red light the eye's pupil doesn't even constrict.
<HR></BLOCKQUOTE>

Time for a non-agressive disagreement and some fill-in information...

The pupilary constriction reaction actually occurs as a result of the intensity of the light regardless of the color. Bright red will cause the pupil to constrict just as much as a bright white light. The constriction serves the purpose of adjusting the quantity of light striking the retina and thereby improving the sharpness of the image. (and if you want to get really picky - what the pupilary constriction/expansion is doing is improving the image of the object you are focusing on when in a high-contrast situation)

For maintaining your "night vision", the best possible source of light is actually a very dim turquoise light - scotopic sensitivity peaks at 500nm, turquoise LEDs are 507nm. To see the same detail with any other color you will need more intense light in that "other" color than you would in turquoise. Since intensity of the light is what disrupts scotopic vision, the very dim turquoise will serve this purpose best.

Photopic vision is most sensitive to 555nm light - yellowish-green.

So.... "at night the eye is not as sensitive to red as it is during the day." is correct - the wavelength shift from photopic to scotopic vision is toward the shorter wavelengths.

But... "In fact, under red light the eye's pupil doesn't even constrict." is not correct as pupiliary contraction occurs as a result of percieved light intensity and contrast, not wavelength. A dim enough light of any color can avoid a pupilary constriction reaction.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Notwithstanding what I said above, the cyan definitely appears much brighter than the amber under normal atmospheric conditions and driven at the same current.
This is probably due to the human eye's increased sensitivity toward green and blue.
<HR></BLOCKQUOTE>

Actually, cyan Luxeon Star LEDs produce more light than any of the other LEDs not because of the sensitivity of our eyes at all, but because they are more efficient in general. This can be objectively measured with light meters.

(Edit) - At least that's what i'm getting from the specs sheet....

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Quickbeam:
Actually, cyan Luxeon Star LEDs produce more light than any of the other LEDs not because of the sensitivity of our eyes at all, but because they are more efficient in general. This can be objectively measured with light meters.

(Edit) - At least that's what i'm getting from the specs sheet....<HR></BLOCKQUOTE>


Hey Guys,

Thanks for all this technical talk. But it's way over my head. I just want to know if I'm stuck in a fog or a building that's burning (smokey) which color led - white or cyan will help me find my way out better (therefore be brighter or have a further visible beam) ?

I'm guessing, from the posts above, that the cyan, being more "bright," would be the one I should purchase ?

thanks,

sylvestor.

Most fog lights are yellow. I really can`t say why. Perhaps research has found that color penitrates further?

Sorry, Sylvestor, we did kind of go "over the top" on that one. Amber would probably be best IMHO - the longer wavelengths tend to penetrate better and the amber is quite bright as well.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
It's absurd to use "scotopic" and LED in the same sentence, as direct LED light, regardless of color, is more than intense enough to trigger a photopic pupilary response.<HR></BLOCKQUOTE>

Sorry that I was not able to make it clear enough.
I do not have much time now, but I'm quoting a very knowledgeable person (D. Gibson):

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
The Photopic curve is quoted for a scene luminance of
10cd/m2, and the scotopic at 0.001 cd/m2. That is quite dark!

Without going into the how-and-why of these units, it is the case that a
3mcd LED (note: 0.003 cd) shone at 3m onto a 100% reflective, perfectly
diffuse surface, will give a scene luminance of 0.001cd/m2, so LED
lighting using "bright" LEDs is far too bright for true scotopic vision.

A working rule is that if you can see colours then the scene is too
bright for scotopic vision.
<HR></BLOCKQUOTE>

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Quickbeam:
Actually, cyan Luxeon Star LEDs produce more light than any of the other LEDs not because of the sensitivity of our eyes at all, but because they are more efficient in general. This can be objectively measured with light meters.

(Edit) - At least that's what i'm getting from the specs sheet....<HR></BLOCKQUOTE>

I do not know which specs you are using, but the latest I have (September 2001) state the same 'brightness' for amber and cyan (600 cd on axis for nominal current).

And your 'effieciency' includes the eye's behaviour. The trick is, that the candela, lumen and lux rating are weighted for the human response already.

And I'm not shure if Dugg refers to a theory about pupil opening, scotopic and photopic response. I will not go into it. Dugg, could you please tell us if it is so?

And sorry for looking aggressive (it was absolutely not my intention): I always have the excuse for using a foreign language .-)

I dunno, I was just going by what my ninth grade science teacher told me:

He said amber sunglasses make things "look brighter" because the eye is tricked by the color into opening the pupil more, which made sense then and still makes sense now.

So I made the possibly erroneous conclusion that an amber LED lighting a bike path would benefit from the same effect.

I have to admit I have not taken measurements of the diameter of my pupils while mountain biking with different colored LEDs

That exercise is left for the student.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Duggg:
I dunno, I was just going by what my ninth grade science teacher told me:

He said amber sunglasses make things "look brighter" because the eye is tricked by the color into opening the pupil more, which made sense then and still makes sense now.<HR></BLOCKQUOTE>

This sounds more like an urban tale, but I will think about it (and collect data).

The theory, which I thought you are referring, says that from medium light levels down (maybe starting at 200 lx) the pupil size is more influenced by the scotopic spectrum (although the eye still works photopic).

But the key point is:

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Earlier posted by Duggg:
Still, from experience, I find the path "easier to see" under cyan light than red or even amber. The best design would probably combine both---cyan for the high beam, and amber for the low beam. That way, distant obstacles can be detected, and closer objects can be more easily scrutinized
<HR></BLOCKQUOTE>

That's exactly what I meant when I wrote 'it depends on your application'. If your light is monochrome at a colour your environment does not reflect, everything will stay very dark. And vice versa.
We are now debating this things for more than a decade among cavers.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>And sorry for looking aggressive (it was absolutely not my intention): I always have the excuse for using a foreign language .-)<HR></BLOCKQUOTE>

Don't worry, PeLu, you weren't appearing aggressive. I just wanted to make sure no-one thought I was being aggressive. I probably should have said "friendly disagreement" instead.

The subtleties of translating phrases between two languages are very difficult to master. I'm always amused how even individual words cannot be directly translated. E.g. "angst" is taken to mean "fear" in English by many people, but I understand it would be more accurately translated as a combination of "anxiety" and "fear". (I hope my understanding is correct or I will feel pretty foolish for mentioning it as an example!)