Remember that neodymium and all other filters *absorb* light. I have
seen no data supporting any claim that GE Reveal lamps provide better
visibility than unfiltered incandescent lamps OF EQUAL POWER AND LIFE.
There have been a few experiments done that compare unfiltered
incandescent lamps to neodymium lamps at EQUAL LUMENS, which is not
the way that real lamps work when you add a neodymium filter.
Absolutely true. If visual acuity worsens at lower light levels and
a neodymium coated lamp AT EQUAL ILLUMINANCE gives equal visual
acuity (both are results I have seen) then it stands to reason that
the reduced illuminance from a filter would result in worse visual
acuity. Now, whether these headlamps do something to increase light output
by increasing wattage (I don't believe the Reveal lamps marketed
for homes do) is another story. I also have no experience to
suggest the filter itself causes shorter life.
We tested "color rendering"* of some neodymium coated headlamps,
equated for EQUAL ILLUMINANCE under the assumption that to meet
headlamp standards a filtered headlamp would have to somehow be
adjusted (by increasing wattage or some other means) to be equivalent
to a typical unfiltered headlamp. Lo and behold, people LIKED the
appearance of colors better under the coated lamps, but their
ability to correctly identify those colors was the same under
the coated lamps as under uncoated halogen and even HID headlamps.
*I use the term "color rendering" loosely here. In fact the
neodymium coated lamps have a CRI of around 80, compared to
around 99-100 for the uncoated halogen lamps, although they do
seem to make certain small color differences stand out more than
unfiltered halogen lamps despite their lower CRI. There is a
system called "gamut area" which roughly estimates the ability
of a light source to render colors so that the relative
chromaticities of the illuminated surface colors, plotted on
a chromaticity diagram, are as far apart as possible. A neodymium
lamp does indeed have a larger gamut area than an unfiltered
halogen lamp but it seems unlikely this improvement has much
bearing on driving safety, given that even HID headlamps allow
people to correctly identify colors. To put that in context,
neodymium headlamps (IF adjusted for EQUAL light output as a
conventional halogen headlamp) might make it slightly easier
to tell if a pedestrian on the edge of the road is more likely
to be a Native American or a Southeast Asian. Great. Kudos to
neodymium for promoting awareness about the cultural diversity
of pedestrians. But is that really an important judgment someone
needs to make while driving? Isn't it enough just to know that
it is a *person*?
As for glare, color seems to play no role in reductions in
visual performance caused by glare from headlights at night,
but "bluer" lights are consistently observed to be a bit more
uncomfortable than "yellower" ones, which is in contradiction
the alleged benefit of the neodymium headlamp, which removes some
"yellow." D. A. Schreuder in the 1970s wrote an excellent
review about "yellow versus white" headlamps (when Belgium,
his home country was allowing both colors in deference to
France who used yellow headlamps and other neighbors who all
used white headlamps) and all of the research he reviewed
pointed to that conclusion.
John
