Re: LED's

[Wallace White <wallace@remdesign.com>]

c a l i b a n wrote:
> 
>         interesting.  also, a plus for led's is that they
>         light up much closer to totally instantly than regular
>         incandescent.  this is a ctually a major reason that
>         they are becoming standard.  

I don't know if that's the reason or not, but it is an added bonus. The
rise time of an LED is usually under 20 ns, while you can watch the
incandescent stop lights and tail lights gradually turn on or off. HP
has cited studies showing that drivers are more likely to notice brake
lights and stop lights that change so quickly, like LED's do.

> also their low voltage
>         usage has made them popular in warning signs, often
>         able to be solar powered and totally off that pesky
>         grid.  traffic signal red lights in many cities have
>         been switched over - and they have this weird effect
>         of "flashing" on, which is probably a good safety
>         feature.  i dunno if it is intentional or not.

I've seen a few of the ones you describe, which seem to have a spike in
brightness right when they come in. Whether it's intentional or not,
it's not a characteristic of the LED itself; it could be an
unintentional characteristic of the drive circuit, but I bet traffic
light designers know what they're doing better than to let that happen.
Anyway, I guess it is supposed to catch your attention even better. I
think it's irritating, especially if the stoplight is in "flash" mode.

- Wallace
  '87 5kcstq 150k