LED bulbs

[Karl W4KRL]

Eric,

That is a good question and I don't have a direct answer. When the bulb is
certified "dimmable" they are certainly referring to some sort of switching
phase control and not a variac. Traditionally the switch was a triac but
could now be a MOSFET. I do not know what makes the dimmer suitable for
CFL/LED applications but from experience I know that the life of CFLs is
greatly reduced on a non-certified dimmer and the dimmer response is very
choppy.

There should not be any problem using the LEDs on a variac. Generally the
front end of the bulb circuitry is a full wave rectifier so it makes little
difference whether it is supplied with phase control or pure sine wave or
even DC. My suspicion is that some dimmable bulbs "read" the phase control
angle and modulate the output accordingly. If that is the case then they
may not dim well on a variac. But your experience is that they do so I
wouldn't worry.

The CFL/LED dimmers I bought have a trimpot to adjust the low end of the
dimming range. When set too low the bulbs may flicker or not start. But
when adjusted properly there is smooth dimming over a good range.

*73 Karl W4KRL*

On Mon, Jan 26, 2015 at 10:08 PM, Eric Carlson <ecarlson at invisiblerobot.com>
wrote:

>   Thanks. And a question below.
>
>   I had a $10 off Staples coupon so I got 3 LED bulbs for $2. Now that
> I've tried them, I might go back for more, if they have any left. Most of
> my house has CFL's or similar, with incandescent in the master bedroom and
> master bath for the best dimming capabilities. I counted about 90 bulbs
> altogether.
>
>   I tried these dimmable LED bulbs with dimmers, and they are pretty good,
> except for the slightly high turn on light level with triac dimmers (I
> assume solid state dimmers still use triacs).
>
>   For the past 30+ years I've been using a variac as a dimmer in the
> master bedroom, to eliminate the audible lightbulb buzzing/ringing
> sometimes caused by triac dimmers, and to provide excellent light control,
> especially at very low light levels.
>
>   Here's the question: I tried these LED bulbs on the variac, and they dim
> very well, even at pretty low light levels. Are these dimmable LED bulbs
> safe to use on a variac? And are there any reasons I shouldn't use them on
> the variac?
>
> - Eric, AJ4LN
>
> On Wed, Jan 14, 2015 at 1:00 PM, <tacos-request at amrad.org> wrote:
>
>> From: Karl W4KRL <W4KRL at arrl.net>
>> Subject: LED bulbs
>>
>> If you want to try LED bulbs but don't want to take out a second mortgage
>> on your home Staples has 800 lumen (60W equivalent) bulbs on sale for
>> $3.99
>> in stores (not online). It is 3000K and dimmable. Sold under the Staples
>> brand but looks very much like a Phillips.
>>
>
>
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