You are right that the dimmer is not the only issue.

Fluorescent lamps can be dimmed to very low levels, but for
that to happen the ballast must supply a high open circuit
voltage and, most importantly, have a very high Thevenin
impedance looking into the output terminals. (Because the
negative incremental impedance of the discharge gets very
large as the current is decreased, and the output impedance
of the ballast must always be larger than the negative
incremental impedance of the lamp for stable operation.)

No low cost ballasts I know of can meet these requirements.

--
Vic Roberts
http://www.RobertsResearchInc.com
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My experience is certainly the same - dimming fluorescents are exponentially
more expensive than their standard counterparts, and that primarily because
of the ballast cost. And unfortunately often accompanied by humming
(vibration etc...)....

I believe that LED'S will ultimately resolve all these issues while using
less energy and providing greater life.

Do you feel the same?

Willy

On 10 Apr 2008 22:20 +0000 UTC Don Klipstein <don@manx.misty.com> wrote:

| Overall luminous efficacy of a tungsten filament varies greatly with its
| temperature. As a result, incandescent lamps have overall luminous
| efficacy severely compromised when they are dimmed.
|
| Put 50 watts into a 100 watt 120V A19 incandescent that produces 1710
| lumens with 100 watts, and what comes out is about 20% of that 1710
| lumens. At half power, overall luminous efficacy is about 40% of that at
| full power.
|
| This effect is a characteristic specific to incandescent lamps,
| including halogen lamps. Fluorescent lamps and LEDs have overall luminous
| efficacy not changing as much as input power is varied.

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?

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

In article <ftnnuf12lua@news5.newsguy.com>, phil-news-nospam@ipal.net wrote:
On 10 Apr 2008 22:20 +0000 UTC Don Klipstein <don@manx.misty.com> wrote:

| Overall luminous efficacy of a tungsten filament varies greatly with its
| temperature. As a result, incandescent lamps have overall luminous
| efficacy severely compromised when they are dimmed.
|
| Put 50 watts into a 100 watt 120V A19 incandescent that produces 1710
| lumens with 100 watts, and what comes out is about 20% of that 1710
| lumens. At half power, overall luminous efficacy is about 40% of that at
| full power.
|
| This effect is a characteristic specific to incandescent lamps,
| including halogen lamps. Fluorescent lamps and LEDs have overall luminous
| efficacy not changing as much as input power is varied.

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 Klipstein (don@misty.com)

On 12 Apr 2008 06:21 +0000 (UTC) Don Klipstein <don@manx.misty.com> wrote:
| In <ftnnuf12lua@news5.newsguy.com>, phil-news-nospam@ipal.net wrote:
|>On 10 Apr 2008 22:20 +0 UTC Don Klipstein <don@manx.misty.com> wrote:
|
|>| Overall luminous efficacy of a tungsten filament varies greatly with its
|>| temperature. As a result, incandescent lamps have overall luminous
|>| efficacy severely compromised when they are dimmed.
|>|
|>| Put 50 watts into a 100 watt 120V A19 incandescent that produces 1710
|>| lumens with 100 watts, and what comes out is about 20% of that 1710
|>| lumens. At half power, overall luminous efficacy is about 40% of
|>| that at full power.
|>|
|>| This effect is a characteristic specific to incandescent lamps,
|>| including halogen lamps. Fluorescent lamps and LEDs have overall
|>| luminous efficacy not changing as much as input power is varied.
|
|>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.

Kind of like the efficacy of dimming with a variable resistor

On 12 Apr 2008 06:21 +00 UTC, don@manx.misty.com (Don Klipstein) wrote:

In art <ftnnuf12lua@news5.newsguy.com>, phil-news-nospam@ipal.net wrote:
In response to my mention of incandescent lamps losing efficiency

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.

In art <ie3204t9bnclekdnpbjv8at4io9j71vbho@4ax.com>, Victor Roberts wrote:
On 12 Apr 2008 06:21 +00 UTC, don@manx.misty.com (Don Klipstein) wrote:

In art <ftnnuf12lua@news5.newsguy.com>, phil-news-nospam@ipal.net 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@misty.com)