R.Lewis wrote:

From what I hear about led traffic lights:
a) the amber & green colors are incorrect and (particularly the ambers)
drift about with temperature .
b) the output falls out of spec with time.
c) a) & b) are ignored.

Is this true?

Partially. When LED traffic signals were in their infancy the specs
were all written around incandescents and so didn't address
characteristics particular to LEDs such as intensity and color drift
over time. The Institute of Traffic Engineers (ITE) just released a
Draft of a proposed spec (although it may now be final) for LED Traffic
Signal Heads for US roads. I don't know what's in effect for Europe, etc.

As for existing LED traffic heads - a number of them are
color-compliant, but there are also a number that are close but do not
fall within the established color parameters (and some that are nowhere
near close). My opinion is that the purchasing agencies ignored or were
not aware of the lack of compliance and went ahead because of the energy
and maintenance savings.

Does anyone measure them ?

My company does as a compliance laboratory. We could (but don't)
measure them in the field. It's VERY expensive.

--
Douglas Cummins
Calcoast - ITL