"Daniel J. Stern" wrote in message
.umich.edu...
On Sat, 12 Nov 2005, JosephKK wrote:

Seems to me I see a lot of trucks with new LED signal/stop lights, and
I can get close enough to see no SAE imprimatur on them. Then I see
celebrities breaking the law. and president's since Nixon, and
presidents circumventing the Consitution since I was born and I have to
wonder what good is the "rule of law?" It is a matter of what I can
get away with - not what is legal. So how bad can LED lights be?

This sub-thread got me curious, so i looked it up found 49cfr564.
Roughly it says if it gives equivalent light (including color
characteristics) and is otherwise interchangeable with original it is
legal. Thus halogen lamps, LED's, induction lamps or whatever are OK.

That is not correct. 49CFR564 contains the specifications for replaceable
headlamp "light sources" (bulbs). The actual Federal requirements for car
lights, contained in 49CFR571.108, actually state the opposite of your
faulty understanding: The design and performance characteristics of every
light source are mandatory, and cannot be selectively modified to suit the
whim of whoever's doing the modification. Any modification -- different
power rating, different filament configuration, replacement of filaments
with arcs or arcs with filaments (or arcs or filaments with LEDs, etc.) --
means it is a different light source, not legally interchangeable.

Furthermore, 49CFR564 contains the specifications only for forward
illumination light sources ("bulbs"). Signalling light sources are not
contained in 49CFR564. The exact legal reason behind the illegality of
"LED bulbs" is a little tricky to follow: When such bulbs are installed,
they spoil the compliance of lighting devices designed to use a filament
bulb of one sort or another, and manufacturer-certified as compliant with
FMVSS108 when using that filament bulb. So it's not the bulb itself that's
illegal to sell, buy or install, it's what happens to the performance of
the vehicle lighting device as a result of installing the "LED bulb".

In actual fact, "LED bulbs" do not produce anywhere near the same amount
of light as a filament-type signalling bulb, nor do they produce anywhere
near the same (Lambertian) distribution of light...even those clever ones
with sideward-facing LED emitters in addition to the rearward-facing
items. Installing "LED bulbs" in bulb-type car lamps doesn't just spoil
their compliance with the applicable safety standards, it spoils their
performance. The light is too dim, the illuminated area is too small, the
intensity ratio between bright (brake or turn) and dim (tail or park) is
improper, and the vertical and horizontal angles of visibility are much
too small. All of this adds up to grossly reduced vehicle conspicuity and
safety.

DS

Thanks Dan

I wondered why my city was replacing the traffic light lamps with led's.
Never knew that they had a smaller field of view. And ya during the summer
sun in the desert you can hardly see them unless there are hoods over the
lens. Ok they probably save a dime or two in maintenance and energy.