Jeff Thies wrote in
:

On 12/24/2010 1:54 AM, Home Guy wrote:
I'm seeing more LED lightbulbs turning up on store shelves.

I don't think I've seen one yet that is ok to use with a dimmer switch.

I haven't really been following, but I was in the borg last night and
they now have quite a few. I noticed, right on the box, of at least one
"Dimmable". There is little reason why not, unless flicker related.


YMMV


I can understand why CFL's can't be put on a dimmer - but why not LED
bulbs?

They're crazy-priced as is.

Getting better. I was looking at bulbs priced in the teens. I seem to
recall prices 3 times higher not long ago. But I'm no expert.

Wound up buying a CFL that looked just light a regular bulb (for $4),
with glass all the way to the screw. Got one floor lamp that a regular
CFL won't screw in.

Jeff


Not being able to dim them makes them even
less desirable as a replacement for incandescent bulbs.



LEDs are CONSTANT CURRENT-driven,not voltage driven.
they have to have some sort of current regulator inside that keeps the
current constant regardless of input voltate swings.
To dim a LED,you would have to vary the input current,and the typical triac
lamp dimmers don't do that,they vary input voltage.

Plus,there's a fairly narrow range of current that produces light from the
LED chip,it's not linear.Most LED dimming schemes pulse modulate the
LED,changing the duty cycle of the current,and the eye averages the output.
you get better efficiency that way,but it's more complex electronically.

--
Jim Yanik
jyanik
at
localnet
dot com