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Cost of electricity for light dimmer

Z

Zarbol Tsar

Jan 1, 1970
0
I have an ordinary room lamp. In the mains lead of the lamp there is
a dimmer device. It is continuously variable from very dim to full
strength.

If I set the dimmer to give me a dim light then do I pay less for the
electricty than if I used the light bulb at full strength?


Thank for any info.
Z.T.
 
S

someone

Jan 1, 1970
0
Zarbol Tsar said:
I have an ordinary room lamp. In the mains lead of the lamp there is
a dimmer device. It is continuously variable from very dim to full
strength.

If I set the dimmer to give me a dim light then do I pay less for the
electricty than if I used the light bulb at full strength?

Yes, but you pay more than you would by using a lamp of lower wattage.

For example with a 100 watt bulb, and the dimmer set to deliver 50 watts,
the lamp may give out approximately the lumens equivalent to a 25 watt
bulb.
 
Z

Zarbol Tsar

Jan 1, 1970
0
Yes, but you pay more than you would by using a lamp of lower
wattage.

For example with a 100 watt bulb, and the dimmer set to deliver
50 watts, the lamp may give out approximately the lumens
equivalent to a 25 watt bulb.

Do you mean that if the dimmer is set at its midpoint to 50 Watts
(insted of the full power of 100 Watts) then I pay only for 50 Watts
consumption?
 
S

SQLit

Jan 1, 1970
0
Zarbol Tsar said:
I have an ordinary room lamp. In the mains lead of the lamp there is
a dimmer device. It is continuously variable from very dim to full
strength.

If I set the dimmer to give me a dim light then do I pay less for the
electricty than if I used the light bulb at full strength?


Thank for any info.
Z.T.


answer depends on the dimmer. Some dimmers just burn off the excess voltage
as heat. Ever notice some of commercial dimmers and the huge heat sinks on
them.

I will bet that if you try an 100 watt lamp and measure it at 100% and then
again at 50% your not going to see much of a difference in the usage. (ahead
of the dimmer)

I once had a museum customer that had huge amounts of track lights on
dimmers. They would put in 100-150 watt bulbs and then dim to around 50%.
Dimmers toasted every 6 months. The load was only about 80% of the rating of
the dimmer. I convinced them to change to 75 watt bulbs and dim 25%. I have
not replaced an dimmer in 5 years. I have not idea if there was just an bad
batch of dimmers or what. Under constant use as far as I am concerned
dimmers are not my friend. I use levels of light which means more fixtures
in my home.
Just my view from the cheap seats
 
T

Tim Wescott

Jan 1, 1970
0
Zarbol said:
Do you mean that if the dimmer is set at its midpoint to 50 Watts
(insted of the full power of 100 Watts) then I pay only for 50 Watts
consumption?
Yes, your consumption goes down so your bill goes down (or should).
Unfortunately your light output goes down faster than your bill, because
light bulbs can't be efficiently dimmed.
 
S

someone

Jan 1, 1970
0
Zarbol Tsar said:
Do you mean that if the dimmer is set at its midpoint to 50 Watts
(insted of the full power of 100 Watts) then I pay only for 50 Watts
consumption?

I don't know where the point would be to get the 50 watts, but the point is
that you would be paying for power that would be consumed by a 50 watt bulb
but getting only the light you would get from a 25 watt bulb. From the
money saving point of view you are ahead to put in a 25 watt bulb (and pay
for only 25 watts of power).

A dimmer is for aesthetic purposes. One little advantage is that the bulbs
usually last longer when run at low power. Savings there still is tiny
compared to the loss of lumens per watt.
 
T

Tzortzakakis Dimitrios

Jan 1, 1970
0
You're wrong both-sorry but that's it.A dimmer is *not* a potentiometer, so
there's no energy consumed on it.Usually it has a triac (which is a simple
power electronic device, like two thyristors in anti-parallel connection).
 
T

Tzortzakakis Dimitrios

Jan 1, 1970
0
The heat sink is for the triac.
 
P

Phil Munro

Jan 1, 1970
0
Zarbol said:
Do you mean that if the dimmer is set at its midpoint to 50 Watts
(insted of the full power of 100 Watts) then I pay only for 50 Watts
consumption?

Here is my take on dimmers.

1) Dimmers do NOT burn off power to accomplish dimming. At least not
the dimmers that we use in residential switching applications, and not
the dimmers that have been available for 30 years or so.

2) There is a very small power loss in the dimmer, but that is NOT
what causes the dimming. Rather the current to the lights is switched
on and off, causing the average (effective) current to be lowered and
therefore the incandescent bulbs are "dimmed." The small size of the
dimmer in the wall box is what causes the "hotness" of the dimmers.
And the higher wattage dimmers have the larger visible heat sinks
because they can carry higher current and therefore dissipate more
(but still small) power.

3) Bulbs should be chosen to allow the level of lighting that would be
the MAXIMUM desired at a location (or the maximum fixture rating), and
then dimmers can be used to allow LOWER levels of lighting when that is
desired.

3a) A more efficient way to accomplish dimming is with switches. For
example, a three bulb fluorescent fixture works nicely with two wall
switches to allow one bulb on, two bulbs on, or three bulbs on. The
bulbs run at maximum efficiency whenever they are on. BUT this requires
an extra wiring and an extra switch, plus it does not allow continuous
dimming. (For fluorescent lighting, dimming is more difficult, so this
method is especially nice.)

4) If the bulb wattage is ALWAYS higher than the desired level of
lighting, then a lower bulb wattage should be used since it gives more
light per watt than a dimmed higher wattage bulb. For example, using a
60 watt bulb to get a certain level of LIGHT is more efficient than
using a dimmed 100 watt bull to get that same level of LIGHT. Look at
the lumens ratings on the two bulb sizes to understand this. Two 60
watt bulbs equals the same LIGHT output (lumens) as one 100 watt bulb.

5) Dimmed bulbs will last longer since their operating temperature is
lower, also:

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).

7) Dimmers go bad when the loads they are controlling is higher than
their ratings. 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.

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.

9) A single standard 600 watt dimmer should last a long time on 400
watts or so. I know lots of examples of this.

OK, my time is up. What have I forgotten? --Phil
 
R

R.Lewis

Jan 1, 1970
0
SQLit said:
answer depends on the dimmer. Some dimmers just burn off the excess voltage
as heat.

Not for the past 40 years they have not - they would be too expensive to
produce.


Ever notice some of commercial dimmers and the huge heat sinks on

I am sure that there will be plenty of respondents explaining the purpose of
these (relatively small) heatsinks.
Have you no idea of the size of heatsink required to 'burn off', say, 100
watts in air and keep the surface temperature of the heatsink below the
hundreds of degrees!!
 
S

someone

Jan 1, 1970
0
Were you replying to a different post than those listed below?

The illumination output of a standard light bulb varies approximately by the
square of the applied power. Cut the power in half and you get about one
fourth the lumens. That is only approximate and varies somewhat with the
type of filament.
 
S

Sylvia Else

Jan 1, 1970
0
Phil said:
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.

This in particular is why you shouldn't use dimmers with lamps that are
mounted so that the filament is above the socket. When such lamps burn
out it is not uncommon for a broken piece of filament to fall and
briefly short across the two thick wires that feed the ends of the filament.

Sylvia.
 
D

Don Klipstein

Jan 1, 1970
0
I have an ordinary room lamp. In the mains lead of the lamp there is
a dimmer device. It is continuously variable from very dim to full
strength.

If I set the dimmer to give me a dim light then do I pay less for the
electricty than if I used the light bulb at full strength?

You pay less with a given lightbulb being dimmed than with the same
lightbulb not being dimmed.

However, if you use a lower wattage lightbulb or fewer lightbulbs you
save even more. Incandescent lightbulbs are very significantly less
efficient at producing light when dimmed.

- Don Klipstein ([email protected], http://www.misty.com/~don/bulb1.html)
 
D

Don Klipstein

Jan 1, 1970
0
Do you mean that if the dimmer is set at its midpoint to 50 Watts
(insted of the full power of 100 Watts) then I pay only for 50 Watts
consumption?

When dimmed to half the power consumption, you pay for 50 watts while
getting less light than a 40 watt lightbulb delivers. This gives
you about 21% of the light of non-dimmed operation, but due to
some economies of scale this is brighter than a 25 watt lightbulb
but still dimmer than a 40 watt one. (It takes about seven 25 watt
lightbulbs to make as much light as a 100 watt one.)
As for the midpoint of the dimmer - it is probably other than this.

Maybe better off with compact fluorescents - get full light with around
25-33% of full power, and equivalent incandescent dimmed to that low a
power consumption is around or just somewhat more than a nightlight.

Splurge a little and you can get a system with dimmable compact
fluorescents. This requires bulbs, fixtures, special dimming
ballasts, and dimmer controls to be compatible with each other - get the
system as a whole.
Disadvantages: 1) The lower limit is probably "brightish nightlight"
2) The color does not change to a warmer color the way
incandescent does when dimmed. Color changes are
much less and more irregular.

- Don Klipstein ([email protected])
 
D

Don Klipstein

Jan 1, 1970
0
You're wrong both-sorry but that's it.A dimmer is *not* a potentiometer, so
there's no energy consumed on it.Usually it has a triac (which is a simple
power electronic device, like two thyristors in anti-parallel connection).

People fear the resistive losses in potentiometer (or rheostat) type
dimmers that have been obsoleted by triac-based ones for decades.

However, a remaining issue is that incandescent lamps operate much less
efficiently when dimmed. As a rough general rule, efficiency of a given
lightbulb at producing visible light varies roughly with the square of
power fed into it. (Roughly, only roughly that is.)

- Don Klipstein ([email protected])
 
D

Dave Platt

Jan 1, 1970
0
Don Klipstein said:
People fear the resistive losses in potentiometer (or rheostat) type
dimmers that have been obsoleted by triac-based ones for decades.

However, a remaining issue is that incandescent lamps operate much less
efficiently when dimmed. As a rough general rule, efficiency of a given
lightbulb at producing visible light varies roughly with the square of
power fed into it. (Roughly, only roughly that is.)

And, as an additional issue, it's generally a bad idea to use a dimmer
with quartz-halogen lamps. When dimmed, the bulbs run a good deal
cooler, the halogen-sequestering-and-redeposition of the tungsten
doesn't work as well, the tungsten tends to plate out on the inside of
the tube and dim the bulb, and the bulb lifetime is greatly decreased.

All in all, as others have said, it makes more economic sense to use
smaller bulbs at full power rather than dimming a high-wattage bulb.
 
D

Don Klipstein

Jan 1, 1970
0
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])
 
D

Don Klipstein

Jan 1, 1970
0
answer depends on the dimmer. Some dimmers just burn off the excess voltage
as heat.

Hardly ever true - more like 1-2% of the line voltage times load current
becomes heat.
Ever notice some of commercial dimmers and the huge heat sinks on
them.

Usually the heatsinks are for dissipation of heat amounting to only 1-2%
of full load power!

Please consider that a 40 watt soldering iron, maybe as little as a 15
watt one, can get the heatsinks much hotter than any normal operation would!
I will bet that if you try an 100 watt lamp and measure it at 100% and then
again at 50% your not going to see much of a difference in the usage. (ahead
of the dimmer)

A 100 watt bulb dimmed to half output consumes about 74 watts. With
losses in the usual dimmers, this amounts to about 75 watts.
I once had a museum customer that had huge amounts of track lights on
dimmers. They would put in 100-150 watt bulbs and then dim to around 50%.
Dimmers toasted every 6 months. The load was only about 80% of the rating of
the dimmer. I convinced them to change to 75 watt bulbs and dim 25%. I have
not replaced an dimmer in 5 years. I have not idea if there was just an bad
batch of dimmers or what.

Most likely:

1. The dimmers were not addequately conservatively designed
2. Dimmers were placed close to each other or in the same box as each
other so that they added heat to each other.

However, lower wattage bulbs dimmed less do indeed give the same light
for less power consumption and less dimmer heating than you get with
higher wattage bulbs dimmed more.

- Don Klipstein ([email protected])
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
someone said:
Yes, but you pay more than you would by using a lamp of lower wattage.

For example with a 100 watt bulb, and the dimmer set to deliver 50 watts,
the lamp may give out approximately the lumens equivalent to a 25 watt
bulb.

I was reading some promiotional stuff on the Lumileds website. They
pointed out that the white LEDs have the advantage that they can be
dimmed, and the color temperature doesn't change, in other words they
don't have the disadvantage of incandescents that as they are dimmed,
the amount of light per watt diminishes.
 
W

Watson A.Name - \Watt Sun, the Dark Remover\

Jan 1, 1970
0
Zarbol Tsar said:
Do you mean that if the dimmer is set at its midpoint to 50 Watts
(insted of the full power of 100 Watts) then I pay only for 50 Watts
consumption?

Say for instance you had four 25 watt bulbs and you needed only 25 watts
of light. Well, you switch on only one. and you get 25 watts of light
and pay for 25 watts of power. But if you dim your 100W lamp to get 25
watts of light, then you might be paying for 50 watts of power. You get
less light per watt when it is dimmed.
 
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