> > > ... If the LED's you are PWM'ing
> > > are for lighting then an LC filter could do the trick. My 
> > > personal opinion is that LED
> > > strobing should never be visble to the end user, which I 
> > > don't think is un-reasonable,
> > > but requires a much higher frequency to acheive than many 
> > > people initially think.
> > 
> > The motion adds another dimension to the question.
> > 
> > Note that the received advice is to PWM raw so that the LED 
> > is operated at either Imax or 0 for best colour rendition 
> > (as I noted earlier today). Adding a filter would cause 
> > colour shift with PWM duty cycle change but would increase 
> > efficiency compared to that at full output for some lower 
> > level settings.
> > 
> > Where were the LED road marker lights that you saw? 
> > Wellington road tunnel? If so, they were probably powered by 
> > inductive power transfer.
> 
> The road marker LED lights I saw were on a section of Cobham Drive here in 
> Hamilton, a couple of years ago. I should have found out more about them while 
> they were there, was probably just a trial installation. They took the place of the 
> existing "cat's eyes" markers.

They were possibly these ones...

http://www.highways.co.nz/techspecs.cfm?pid=7&cid=13

Arrgh!! Standard Frequency = 100 pulses / sec.

You have to wonder why really. Do they want the pulses to be visible? Would 1kHz 
or 10kHz really make their switching electronics consumer that much more power? 
LED light output would be the same.

-- 
Brent Brown, Electronic Design Solutions
16 English Street, St Andrews,
Hamilton 3200, New Zealand
Ph: +64 7 849 0069
Fax: +64 7 849 0071
Cell: +64 27 433 4069
eMail:  brent.brown@clear.net.nz


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