Re: Dimmable CFLs? Spectacular Failures?

On Sun, 13 Apr 2008 06:13:00 +0000 (UTC), don@xxxxxxxxxxxxxx
(Don Klipstein) wrote:

In art <ie3204t9bnclekdnpbjv8at4io9j71vbho@xxxxxxx>, Victor Roberts wrote:
On 12 Apr 2008 06:21 +00 UTC, don@xxxxxxxxxxxxxx (Don Klipstein) wrote:

In art <ftnnuf12lua@xxxxxxxxxxxxxxxxx>, phil-news-nospam@xxxxxxxx wrote:
<In response to my mention of incandescent lamps losing efficiency
bigtime when dimmed>

What is the luminous efficacy _change_ of an LED when it is operated by
pulsing the DC power to it, at levels full and zero, with a 50% duty
cycle for each level, at a rate of 1000 Hz?

Unchanged, except very slight increase due to the LED running cooler.

Same question, but change lamp to incandescent, and change frequency to
0.001 Hz.

Basically unchanged - extremely slight decrease for a tiny bit of that
1,000 second cycle with the filament being at temperature significantly
below "full" but significantly above ambient.

The decrease is significant when the frequency gets high enough for the
filament to have significant operation at in-between temperature.

Don't you mean "frequency gets low enough" in the last sentence.

So far, if I haven't brain-farted too badly, I thought I was falling
into discussion of how overall luminous efficacy of an incandescent varies
from "its normal" when PWM-ed with 50% duty cycle at 1/1,000 Hz, or period
of 16-2/3 minutes. As in 8 minutes 20 seconds on, 8 minutes 20 seconds
off.

I would think that every incandescent I ever saw, when given "full
power" at a 50% duty cycle at 8 minutes 20 seconds "on and 8 minutes 20
seconds "off", has its overall luminous efficacy (ratio of photometric
output to energy consumption) close to that achieved with continuous
operation.

When I said "frequency high enough", I meant on-time and off-time
getting down to a couple seconds or fraction of a second, so that the
filament does some significant part of its glowing while not fully warmed
up. As in frequency being increased from .001 Hz to at least a goodly
fraction of a Hz, especially a few Hz.

At maybe around 1 Hz to a few Hz frequency, it appears to me that
50%-duty-cycle operation of most incandescents will have the filament
spending a fair amount of time glowing at "less-than-full" temperature,
and accordingly with decreased "overall luminous efficacy".

- Don Klipstein (don@xxxxxxxxx)

You are correct. I thought you were starting at 1000 Hz and
moving down to where the mattered, instead of starting at
1/1000 Hz and moving up.


--
Vic Roberts
http://www.RobertsResearchInc.com
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