Two 60
watt bulbs equals the same LIGHT output (lumens) as one 100 watt bulb.
True, but this argues against dimming.
Better would be to point out that a 100 watt bulb dimmed to the
brightness of a 60 watt one consumes about 73-74 watts.
And that a 100 watt bulb dimmed to consume 60 watts produces about 21%
of its full output, which is less than that of a 40 watt lightbulb.
Now for the bonus extra trickery: Using fewer lightbulbs is better than
using lower wattage ones, as long as you get adequate light distribution.
Higher wattage lightbulbs are slightly more efficient. There is more than
one reason, but one is that thicker filaments can be operated at a higher
temperature (better for radiating visible light as opposed to infrared)
for a given life expectancy.
5) Dimmed bulbs will last longer since their operating temperature is
lower, also:
True, but for among different ways of achieving a given light output
lower wattage (or better still fewer) undimmed bulbs will cost less than
dimmed ones. In most of the USA, the cost of the electricity is so much
more than the cost of buying replacement bulbs that it pays to consider
energy efficiency.
6) Using a ROTARY (or slide) on/off dimmer (which brings the light level
up from zero) is better for the life of the bulbs, since it minimizes
start-up surge current. I know there has been difference of opinion on
this, but I am convinced that my opinion is fact. Do not buy the PUSH
on/off dimmers; they will shorten bulb life, and may shorten dimmer
life, also (see #8).
A few bulbs benefit from "soft starting", many and probably most do not.
Most (but not all) bulbs have zero or negligible fatigue damage to the
filament from a "cold start" despite a cold start jolting the filament to
cause a "ping" sound that is audible at close range.
It is true that most incandescents fail at a cold start. However, for
most models, the actual damage is caused mainly by operating hours. One
thing that is true (for most lightbulbs) is that an aging filament becomes
unable to survive a cold start just a little before it becomes unable to
survive continuous operation.
There is a usual prelude-to-failure uneven evaporation of the filament.
That process causes a "thin spot" that is subject to a temperature
overshoot during a cold start. In most lightbulbs, such a "deadly thin
spot" is a deterioration mode of the filament that accelerates at a rate
worse than exponentially (during operation) once it becomes significant.
This means that for most lightbulbs, when they become unable to survive a
cold start their operating hours are numbered. And for most (but not all)
lightbulbs, cold starts do zero to usually-negligible damage until the
filament has aged enough for a cold start to be fatal.
7) Dimmers go bad when the loads they are controlling is higher than
their ratings.
True, but they usually don't blow out immediately unless the overload is
very severe. Mild to moderate overload merely shortens their life.
Also, putting more than one dimmer in a box causes
a derating of its power capability. For example, the standard 600 watt
dimmer (with no extra heat sink) gets a smaller rating when more than
one of them are in a ganged box.
True - the power rating of a dimmer usually assumes that there are no
adjacent dimmers adding heat (of just a couple to a few watts - that is
significant!).
8) Dimmers also go bad when a bulb filament sags and causes a high
current surge when it burns out. This happens more often with the
push on/off dimmers since the push on/off dimmers cause a surge of
current which mechanically breaks an old filament. Ever heard the
"singing" of a bulb on a dimmer circuit? This is a similar mechanical
vibration of the bulb filament.
Current surge from burnout is often worse than the current surge of a
cold start. Often when the filament breaks, an arc forms across the gap.
The arc can be encouraged by the voltage gradient across the filament to
expand and go across the ends of the filament, in which case the filament
is no longer limiting current through the arc. This is what causes the
"bright blue flash" that sometimes occurs during a burnout, especially a
burnout during a cold start (when the filament resistance is less and
allows more current to flow through the arc which makes the arc hotter and
more conductive).
Most lightbulbs have fusible links in one of their internal lead-in
wires so that a "burnout arc" does not pop a breaker or blow a fuse.
However, this may be inadequate for protection of dimmers.
9) A single standard 600 watt dimmer should last a long time on 400
watts or so. I know lots of examples of this.
I believe probably true. It gets more uncertain when you have a 600
watt or 540 watt load on a 600 watt dimmer, and it gets worse when you put
more than one dimmer in the same box since each one adds heat to the
others (despite the loss in each dimmer being only a few watts).
- Don Klipstein (
[email protected])