LED / HID wavelength ?

WOW! I been away for some time now, and it's great to see so much power are coming from LED lights. I have one question though, probably a dumb one. But is it possible for a LED bulb, even dare to say HID bulb to put out multiple wavelength in light? It just seems that when i compare lights, from a standard incandescent vs LED, at night, I always seems to be able to see farther with the incandescent, than with a LED. I'm guessing that it is because the LED does not put out all or only partial wavelength from the visible light spectrum? If this is true, then would a multple color LED light be more useful?

Just curious.

Before my spectrometer broke, I took this spectrum of a typical Nichia white LED.
The spectrum is deficient in violet, blue-violet, blue-green, and red. This might account for your seeing "better" with incandescent flashlights.

The other possibility here is the ability for the light to "throw", or travel longer distances. Incandescent flashlights can usually do a better job at this than LED flashlights.

thanks telephony,
maybe it wasn't an apple to apple comparison. Just seems that my eyes were struggling with the LED spectrum

For example, i shined my surefire 8nx at a tree, then shined my Inova X5 LED at the same tree. Though both lit up the tree, the details were not there with the LED. Details meaning the color spectum of the tree. It was an orange tree. The oranges didn't stand out as quickly with LED. The branches looked almost gray color, than in brown.
Kelvin temp. seems to be the factor. The cooler light seems to produce lots of contrast too.

I like to test out the new SF U2 to the X5 to see if it makes a difference at night.

Some people see they can see farther with incadencets. It's the opposite with me. The yellowishness of the beam just looks dark but a whiter beam seems to bring out the contrast more. Good point Craig about the focusing of leds vs incadecents. Most leds don't throw as far as incandents, but not all /ubbthreads/images/graemlins/wink.gif

Warhoggie, another good point. It may depend on the type of LED. I'm refering to luxeons, and you have 5x Nichia 5mm leds. Those tend to be more on the blue side and may not show contrast as well as a luxeon. Plus it could be the surface, as orange will refelct yellows from incadecents more than a blue tinted led. Also our eyes may be more responsive to diff wavelengths.

See what you find with the U2 or any other luxeon, I think you'll be surprised.

IsaacHayes, that kinda makes sense. Would you be able to help out on why LED lighting seems to produce more contrast than incandescent?

Also, I believe it was the French who invented the "yellow" color fog lights. Supposely, our eyes can see better at night with the yellow color. I don't know if everyone will agree with it.

Though, most car companies has gone away from the "yellow" look. 'Cept maybe Lexus, who still use it on their fogs.

Our eyes have two modes of visibility

Photopic vision has a peak sensitivity of 555nm (or green), and is how we see in the daytime.

Night vision is called scotopic vision, and it peaks at 507nm, or blue-green. At night, our eyes are more sensitive to blue-green light than yellow light.

In fact, if you normalize our (night-adapted) eyes sensitivity to be 1.0 at 507nm, then our sensitivity to blue light (around 470nm) would be about 0.68; for yellow light (around 590nm) it's only 0.06! Our eyes are more than 10 times more sensitive to blue light at night than they are to yellow light at night.

White LEDs are strong in the blue and green parts of the spectrum. Incandescents are typically weak in those parts of the spectrum. In addition, our eyes are built to provide contrast and detail information from the green part of the spectrum.

So white LEDs output more light at the wavelengths which our eyes use to perceive detail in objects, thus increasing contrast. And they output more light (proportionally) than incandescents in the regions our eyes are most sensitive at night.

This link gives more information about photopic and scotopic vision:
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html#c2

Yellow is to cut through fog, and not reflect back so bad when it hits the droplets of water. But I can't stand the color. I like whiter headlights as the road surface and just everything seems more clear.
I belive it's because while LED is not full spectrum, it is more white than incandecents. Even on fresh batteries, it will look yellow/orange compared to an LED. So the lack of tint a good pure white led has I belive helps it have more contrast. Plus at night our eyes are more sensitive to blue end of light instead of the yellow-green end and probably accounts for some of it.

I can take a brighter incandecent that goes farther than a dimmer LED, and see just as good with the LED even though less light is coming back at me. All I know is I like it /ubbthreads/images/graemlins/smile.gif LEDs = white light that doesn't get yellow as it dims, nice smooth beams, no bulbs to break, cool techno factor, pure saturated colors (blue, cyan, etc), good stuff! /ubbthreads/images/graemlins/thumbsup.gif

I also find seeing with LEDs much better. With incandescents, things just look "flat", as if viewed on a TV screen. With the greater contrast of LEDs, and the more accurate color, everything looks more natural. I say colors look more accurate with LEDs despite the lower CRI because while LEDs may be deficient in certain wavelengths, incandescents are relatively deficient in lower wavelengths even though all wavelengths are present. This results in blues looking purplish, violets looking almost black, and green plants looking a sickly yellow. This is despite the fact that incandescents have a CRI of 100. The color temp is just all wrong for seeing things naturally, which is why I use high CRI, 5000K fluorescents for all my room lighting. I can't even stand to be in a room lit with incandescents.

Subjectively, LEDs of a given lumen output seem at least twice as bright as incandescents of the same lumen output. I've done many experiments with this, and the results are always the same-you only need about half the lumens with LEDs as you do with incandescents to get the same apparent brightness. This is because LEDs produce more light in the wavelengths of greatest scotopic sensitivity. For similar reasons 5000K fluorescents of a given lumen output seem brighter than 4100K tubes of the same lumen output. I've done side by side comparisons which confirm this.

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evan9162 said:
Our eyes have two modes of visibility

Photopic vision has a peak sensitivity of 555nm (or green), and is how we see in the daytime.

Night vision is called scotopic vision, and it peaks at 507nm, or blue-green. At night, our eyes are more sensitive to blue-green light than yellow light.

In fact, if you normalize our (night-adapted) eyes sensitivity to be 1.0 at 507nm, then our sensitivity to blue light (around 470nm) would be about 0.68; for yellow light (around 590nm) it's only 0.06! Our eyes are more than 10 times more sensitive to blue light at night than they are to yellow light at night.

White LEDs are strong in the blue and green parts of the spectrum. Incandescents are typically weak in those parts of the spectrum. In addition, our eyes are built to provide contrast and detail information from the green part of the spectrum.

So white LEDs output more light at the wavelengths which our eyes use to perceive detail in objects, thus increasing contrast. And they output more light (proportionally) than incandescents in the regions our eyes are most sensitive at night.

This link gives more information about photopic and scotopic vision:
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/bright.html#c2

[/ QUOTE ]

WOW,,, Thank you.

I knew I could see better with white LEDs. This confirms it. I'm refering to closeup work with my firefly or ARC4+ shining bright.

Thanks evan9162 for that very informative post.

BTW I think there is a big diference in color rendition between light comming from 5 mm. Nichia style white LEDs and light comming from Luxeon Stars. I think LS does a far better job in this aspect. Perhaps you could confirm this Telephony, if you have a spectrum of a LS?

Jan

[ QUOTE ]
JanCPF said:
...Perhaps you could confirm this Telephony, if you have a spectrum of a LS?

[/ QUOTE ]
Hi Jan,

My spectrometer does not work anymore, but I think I have an old spectrum of an LS...let me check that, BRB...



And here's that spectrum of a Nichia 5mm white again, just for reference purposes...



That "hump" around 700nm in both spectra is a detector sensitivity issue, and should be ignored.
Hope these spectra are helpful. /ubbthreads/images/graemlins/smile.gif

Thanks Craig. I'm not really sure that the spectrum backs up my statement about color rendition, but anyway thats how I perceive it.

Jan

Thanks guys, good stuff here.

It does, as you can see the yellow bump is larger with the luxeon.

About the color rendition: Nichias are much better then luxeon stars....

CRI Nichia: 85
CRI LS: 70

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Wim Hertog said:
About the color rendition: Nichias are much better then luxeon stars....

CRI Nichia: 85
CRI LS: 70

[/ QUOTE ]
That may have to do with the fact that the Nichia spectrum is less "spiky" than the LS spectrum.

Just for informational purposes, CRI only has to do with the ability to distinguish between colors, not with absolute accurate color rendering. For example, an incandescent has a CRI of 100, which basically means it's easier to tell two close colors apart that it is under an LED with a CRI of 70. However, this says nothing about how accurately those colors are rendered, and in fact under incandescents only reds through yellows look fairly natural. Greens, blues and especially violets render horribly. One possibility suggested for future LED general lighting has been something called equal energy white(EEW). This is basically a spectrum where all visible wavelengths are present in relatively equal amounts (i.e. the spectral distribution is flat). This differs from blackbody curves of any color temperature, although technically speaking EEW has a CCT of 5457K and a CRI of 95. When I read about this, a new parameter called the full-spectrum index (FSI) was used to compare different light sources to EEW, which has a FSI of 0. The higher the FSI, the worse the light was considered. Some examples were as follows-GE Chroma 50 fluorescent (FSI=0.45), Agilent 5mm white LED (FSI=1.28), Lumileds Luxeon Ring 6 (FSI=1.65), soft white 60W incandescent (FSI=8.58). This explains to me anyway why incandescents fair so poorly in the general lighting department despite their CRI of 100, and why even today's Luxeons would be superior. You can read the complete report here

jtr1962,

Great info! - This is very interesting /ubbthreads/images/graemlins/thumbsup.gif

Jan