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#1
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"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? |
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#2
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"white" LED's vs. incandescent and halogen lights
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 |
#3
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"white" LED's vs. incandescent and halogen lights
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 |
#4
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"white" LED's vs. incandescent and halogen lights
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. |
#5
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"white" LED's vs. incandescent and halogen lights
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 |
#6
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"white" LED's vs. incandescent and halogen lights
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 |
#7
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"white" LED's vs. incandescent and halogen lights
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 |
#8
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"white" LED's vs. incandescent and halogen lights
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 |
#9
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"white" LED's vs. incandescent and halogen lights
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 |
#10
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"white" LED's vs. incandescent and halogen lights
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Hash: SHA1 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 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (MingW32) iD8DBQFLGmPkHEhZ5Ws5poERAvvSAJ0W3PvQORwWZpThH8yeQt RY8IHQYwCgknQH JOCmBePW3Lq0aJotKwup5/Q= =kjhF -----END PGP SIGNATURE----- |
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