Re: advice needed (long)

In article <AB_hf.94488$qk4.4613@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
"TKM" <nomail@xxxxxx> writes:
> Too bad low voltage never caught on for traffic signals.

I think all the mains voltage traffic signals vanished from the
UK about 30 years ago. 24V halogen capsules are used (some makes
might use other voltages -- not sure how universal the 24V is).
However, they are driven with a programmed voltage profile (at
least in some systems) to give good on/off times (e.g. preheated
to just below visible a second before the ON time, and then get
a voltage spike to give a quicker ON time). Also, the ON voltage
is varied with ambient light levels to remain visible in bright
sunshine, yet non-dazzling at night. Sometimes this is proportional
control, othertimes just two levels triggered by streeplamp night
sensor. Some control circuits also monitor current draw so they
can remotely signal lamp failure, but I don't know how common it
is to actually provision the remote signalling. (It is much rarer
to see a traffic signal out than it used to be 20-30 years ago.)

Of course, LED's are starting to take over in some places now.
However, I've seen a number of these where one of the LED strings
has died, so the traffic signal lense has some odd shaped dark
area.

--
Andrew Gabriel
.

Relevant Pages

  • Re: advice needed (long)
    ... >> Too bad low voltage never caught on for traffic signals. ... > is to actually provision the remote signalling. ... I've seen a number of these where one of the LED strings ...
    (sci.engr.lighting)
  • Re: Light bulb keep on burning out
    ... traffic signals ... slightly lower voltage. ... have seen the bulbs, they were big on ... back when they used incandescents for all colors. ...
    (alt.home.repair)
  • Re: Light bulb keep on burning out
    ... traffic signals ... slightly lower voltage. ... have seen the bulbs, they were big on ... back when they used incandescents for all colors. ...
    (alt.home.repair)