> > > > 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):
> ? is a bit offset from the LED dip at 475 nm.
> ? Also, I should have been clearer; cones are more sensitive to red
> than to blue.
explanation for perceived LED problems. The yellow phosphor is almost
exactly (and not by accident) where you'd want it to be to maximize
luminous efficiency (the CIE y-bar color matching function and the
yellow phosphor both peaking at about 550 nm)
> 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.