Re: Stocked up with 100w bulbs yet?!


"Derek Geldard" <impex@xxxxxxxxxxxxxxxxxx> wrote in message
news:9cgdm4hr6a3gv6anarka74m7ggvnfq7so0@xxxxxxxxxx
On Thu, 8 Jan 2009 14:34:32 -0000, "M.I.5¾"
<no.one@xxxxxxxxxxxxxxxxxxxxxx> wrote:


LEDs can be powered such that they emit continuous light (like if you
power
them from a DC supply). But, it seems that if you power them with a
pulsed
supply, then the light output is also pulsed and the eye does it's
persistence of vision trick to interpret light when there is none.

AFAIK your eyes simply average the light over the time of persistence
of vision. They work by the light bleaching chemicals in the retina,
they have no capacity to sample and hold the peaks. BICBW.

Thus if
you look at LED car tail lights in the right way (i.e. if you cause the
light to move across your field of vision) you can see that they are, in
fact, flashing. I noticed that the LED christmas tree lights that I have
just put away were similarly flashing. As I said previously, there is no
other technical reason to drive the LEDs such that they flash.

It could be a function of the LED's that they give out proportionately
more light with more current but are strobed to reduce average heat
dissipation.


The heat dissipation is approximately proportional to the square of the
average current as indeed is the light output. Providing the current in
larger but short pulses would offer no advantage over powering the LEDs from
DC.



.

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