In article Wov8h.3279$_x3.1085@trndny02, Marilyn & Bob wrote:

"Don Klipstein" wrote in message
...
In article , Bob F wrote:

"Don Klipstein" wrote in message
I once tested one of those "stick on buttons" claimed to double the
life
of an incandescent, for voltage drop. It dimmed a 100 watt incandescent
enough to increase its life a good 50%.

Unfortunately, dimming incandescents results in even more
power consumed per unit of light produced.

Yes, well enough known! Power consumption varies with applied RMS
voltage to the 1.5 to 1.57 power or so, while light output varies with
applied RMS voltage to roughly the 3.4 power (more with more severe
dimming). That means light output goes down slightly worse than square of
power input, or energy efficiency varying slightly more than
proportionately with square root of light output (roughly light output to
the .55 power, more for severe dimming).
As in to dim to 50% of light output, power input is maybe about 73% of
"full".

Since most of the cost of operating incandescents is normally
electricity cost, I would put some work into increasing the energy
efficiency. As in making some bulbs turn off when you want less light.

When dimming is done with a resistor (as opposed to a variable
transformer or the usual waveform-chopping "phase control" circuit that
usually has a triac), the energy efficiency story gets worse. To count
power consumed by the infected lamp and the resistor, power consumption is
typically proportional to the lamp's RMS voltage to the .5-.57 power.
This means power conmsumption goes down about 1/6 as much as light output
does (when the percentages are small).
The "stick-on button" that dimmed a 100 watt incandescent lamp enough to
increase its life 50% also reduced the light output by about 11% while
power
consumption by the lamp and the "button" was about 98.2 watts (decreased
about 1.8%). Better to just use a longer life incandescent. Depending on
application, often (probably usually) better still to use a compact
fluorescent!

- Don Klipstein )

But don't longer life incandescents do the exact same thing as your
"button", giving you less lumens per watt?

The "button" is worse in terms of energy efficiency. The "button" has
its own resistive losses in addition to reduction of energy efficiency of
the lamp that it is applied to.

- Don Klipstein )