"white" LED's vs. incandescent and halogen lights

It's obvious that the mundane "white" LED bicycle lights do not light
up the asphalt roads very well. Incandescents, halogens, and sodium
lights do better. There seem to be a lot of oranges and yellows on
the illuminated asphalt surface.

My question is why does it appear this way?

I presume that the yellow-orange-red spectral emissions from the LED's
are weaker than the blues. The blues are voltage induced while the y-
o-r's are secondary from phosphors in the casing. Therefore to help
refine my question,

1. Do the stronger blues in the LED cause the weaker yellow/orange/
reds to be less perceived?

2. Are the yellows and oranges on the asphalt caused by sulfur
compounds or by dust and dirt embedded in the tarry surface?

Dear me:

On Dec 4, 3:50*pm, me wrote:
It's obvious that the mundane "white" LED bicycle
lights do not light up the asphalt roads very well.

Emitted watts in the fraction or single digit watts.

*Incandescents, halogens, and sodium lights
do better.

Tens to hundreds of watts.

*There seem to be a lot of oranges and yellows on
the illuminated asphalt surface.

My question is why does it appear this way?

They are painted that way. People that are not fully color blind can
tell the difference, the paints wear well, and they do not bleach too
fast.

I presume that the yellow-orange-red spectral
emissions from the LED's are weaker than the
blues.

The LEDs probably emit only blue, and have the other colors formed by
scattering. Much like the "white light" from a fluorescent light.

*The blues are voltage induced while the y-
o-r's are secondary from phosphors in the casing.
*Therefore to help refine my question,

1. *Do the stronger blues in the LED cause the
weaker yellow/orange/reds to be less perceived?

No, I believe it is a sensitivity in the eye. Blue takes more photons
to fire. Especially for eyes that are triggering mostly rods (black
and white) rather than cones (color).

2. *Are the yellows and oranges on the asphalt
caused by sulfur compounds or by dust and dirt
embedded in the tarry surface?

Probably just scattering losses. Energy is lost, which reduces the
wavelength. And the rod/cone thing.

My two cents.

David A. Smith

dlzc wrote:
Dear me:

On Dec 4, 3:50 pm, me wrote:
It's obvious that the mundane "white" LED bicycle
lights do not light up the asphalt roads very well.

Emitted watts in the fraction or single digit watts.

Incandescents, halogens, and sodium lights
do better.

Tens to hundreds of watts.

There seem to be a lot of oranges and yellows on
the illuminated asphalt surface.

My question is why does it appear this way?

They are painted that way. People that are not fully color blind can
tell the difference, the paints wear well, and they do not bleach too
fast.

I presume that the yellow-orange-red spectral
emissions from the LED's are weaker than the
blues.

The LEDs probably emit only blue, and have the other colors formed by
scattering. Much like the "white light" from a fluorescent light.

The blues are voltage induced while the y-
o-r's are secondary from phosphors in the casing.
Therefore to help refine my question,

1. Do the stronger blues in the LED cause the
weaker yellow/orange/reds to be less perceived?

No, I believe it is a sensitivity in the eye. Blue takes more photons
to fire. Especially for eyes that are triggering mostly rods (black
and white) rather than cones (color).

2. Are the yellows and oranges on the asphalt
caused by sulfur compounds or by dust and dirt
embedded in the tarry surface?

Probably just scattering losses. Energy is lost, which reduces the
wavelength. And the rod/cone thing.

My two cents.

David A. Smith

But if you compare an LED bicycle light to a comparable halogen bicycle
light, you'll prefer the LED. to paraphrase, "there's no substitute for
more power."

nate

(and injection is nice, but I'd rather...)

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

dlzc wrote:

The LEDs probably emit only blue, and have the other colors formed by
scattering. Much like the "white light" from a fluorescent light.

Scattering? It's fluorescence. A UV LED excites
a set of phosphors that emit white light. That's
what a white LED is.

On Dec 4, 2:50*pm, me wrote:
It's obvious that the mundane "white" LED bicycle lights do not light
up the asphalt roads very well. *Incandescents, halogens, and sodium
lights do better. *There seem to be a lot of oranges and yellows on
the illuminated asphalt surface.

My question is why does it appear this way?

I presume that the yellow-orange-red spectral emissions from the LED's
are weaker than the blues. *The blues are voltage induced while the y-
o-r's are secondary from phosphors in the casing. *Therefore to help
refine my question,

1. *Do the stronger blues in the LED cause the weaker yellow/orange/
reds to be less perceived?

"White" LEDs have a strong peak in the blue and a nearly Gaussian
curve centered in the green, extending from the blue-green to the red.
They're kinda weak in the tails. Do a Google Image search for "white
led spectrum" and see for yourself.

The other lamp types you mention are stronger in the red, which the
eye is more sensitive to, particularly at night.

2. *Are the yellows and oranges on the asphalt caused by sulfur
compounds or by dust and dirt embedded in the tarry surface?

Asphalt may look black to the casual glance, but reflectance spectra
tell the tale:

http://www.geog.utah.edu/~chen/

Click on the various locations, check out the various surfaces.
Notice for instance "new paving, dark black asphalt, not mixed with
gravel":

http://www.geog.utah.edu/~chen/aspd2.html

is pretty flat, but "old, dirty asphalt paving":

http://www.geog.utah.edu/~chen/aspa.html

rises from the short wavelength (blue) to the long wavelength (red)
end.

...dirty asphalt just reflects red better.


Mark L. Fergerson

On Dec 4, 3:50*pm, me wrote:
2. *Are the yellows and oranges on the asphalt caused by sulfur
compounds or by dust and dirt embedded in the tarry surface?

I don't see them. I see shades of blue-gray, which is nearly useless
when walking over dark surfaces. Even moonlight is better than white
LEDs.

DB

On Dec 4, 9:30*pm, " wrote:
On Dec 4, 2:50*pm, me wrote:

It's obvious that the mundane "white" LED bicycle lights do not light
up the asphalt roads very well. *Incandescents, halogens, and sodium
lights do better. *There seem to be a lot of oranges and yellows on
the illuminated asphalt surface.

My question is why does it appear this way?

I presume that the yellow-orange-red spectral emissions from the LED's
are weaker than the blues. *The blues are voltage induced while the y-
o-r's are secondary from phosphors in the casing. *Therefore to help
refine my question,

1. *Do the stronger blues in the LED cause the weaker yellow/orange/
reds to be less perceived?

* "White" LEDs have a strong peak in the blue and a nearly Gaussian
curve centered in the green, extending from the blue-green to the red.
They're kinda weak in the tails. Do a Google Image search for "white
led spectrum" and see for yourself.

* The other lamp types you mention are stronger in the red, which the
eye is more sensitive to, particularly at night.

Red map lights are used to preserve dark adaptation because rods _do
not_ respond to them. Rods are most sensitive somewhere in the blue-
green. Do a google image search on "rod sensitivity," etc. Combine
with your previous google image search and you will find that the peak
sensitivity for rods coincides with the "dip" in the typical white LED
spectrum.

-pm

me wrote:

It's obvious that the mundane "white" LED bicycle lights do not light
up the asphalt roads very well. *Incandescents, halogens, and sodium
lights do better. *

"Mundane" 5mm white LEDs are very low-powered-- typically .07 watts
each-- with poor color rendition. Often, these are overdriven at
around 0.2W to squeeze a bit more light out of them, but this has the
side effect of pushing their color balance farther into the blue
range.

Quality high-flux LEDs like Luxeon, Cree, or Seoul Semiconductor
emitters of nominally 1W or more are not only very bright, but also
very reasonable in their color balance. DiNotte, Niterider, Light &
Motion, Cygolite, Busch & Mueller, and other reputable manufacturers
use high performance, color graded LEDs in their better lights. The
results are categorically better than incandescents (halogen, krypton,
etc.) of similar power.

Generic 5mm white LEDs cost a few cents each at the wholesale level.
They are excellent in terms of cost-effectiveness and power
efficiency. But if you want to see things rather than just be seen by
other road users, you'll need either lots of them, or else better
quality lighting.

Chalo

On Dec 4, 10:18*pm, pm wrote:
On Dec 4, 9:30*pm, " wrote:



On Dec 4, 2:50*pm, me wrote:

It's obvious that the mundane "white" LED bicycle lights do not light
up the asphalt roads very well. *Incandescents, halogens, and sodium
lights do better. *There seem to be a lot of oranges and yellows on
the illuminated asphalt surface.

My question is why does it appear this way?

I presume that the yellow-orange-red spectral emissions from the LED's
are weaker than the blues. *The blues are voltage induced while the y-
o-r's are secondary from phosphors in the casing. *Therefore to help
refine my question,

1. *Do the stronger blues in the LED cause the weaker yellow/orange/
reds to be less perceived?

* "White" LEDs have a strong peak in the blue and a nearly Gaussian
curve centered in the green, extending from the blue-green to the red.
They're kinda weak in the tails. Do a Google Image search for "white
led spectrum" and see for yourself.

* The other lamp types you mention are stronger in the red, which the
eye is more sensitive to, particularly at night.

Red map lights are used to preserve dark adaptation because rods _do
not_ respond to them. Rods are most sensitive somewhere in the blue-
green. Do a google image search on "rod sensitivity," etc. Combine
with your previous google image search and you will find that the peak
sensitivity for rods coincides with the "dip" in the typical white LED
spectrum.

The ~430 nm rod peak (beware line wrap):

http://www.ecse.rpi.edu/~schubert/Li...unctions.jp g

is a bit offset from the LED dip at 475 nm.

http://www.mvlc.info/images/photos/led/spectral3.jpg

Also, I should have been clearer; cones are more sensitive to red
than to blue.

IMO though WRT the OP's question the deal-breaker is the greater
reflectivity of asphalt in the red independent of light intensity;
illuminated by incandescent etc. lamps it has red-orangish highlights
as the OP says, but under LED illumination it's just black.

There's also the time factor:

http://www.phys.ufl.edu/~avery/cours...adaptation.gif

If one doesn't ride long enough to get dark-adapted, the greater
sensitivity of the rods doesn't come into play.

Anyway, isn't the point of a headlight partly to get the rider's
vision out of the scotopic and at least into the mesopic regime?

Personally I have no problem with bluish LEDs while night biking. To
me it doesn't look "wrong", just different.


Mark L. Fergerson

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dlzc wrote:
Dear me:

On Dec 4, 3:50 pm, me wrote:
It's obvious that the mundane "white" LED bicycle
lights do not light up the asphalt roads very well.

Emitted watts in the fraction or single digit watts.

Incandescents, halogens, and sodium lights
do better.

Tens to hundreds of watts.

That is an unfair comparison--the _light_ power output of a halogen bulb
is much less than a modern LED for the same electrical power input.

- --
Brendan Gillatt | GPG Key: 0xBF6A0D94
brendan {a} brendangillatt (dot) co (dot) uk
http://www.brendangillatt.co.uk
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