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
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.
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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
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
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Phil Munro Dept of Electrical & Computer Engin
mailto:PcMunro@cc.ysu.edu Youngstown State University
Youngstown, Ohio 44555
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.
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.
Thst's not because they "burn off" the excess voltage. They still work under the principle of delaying switching the current on for part of the AC cycle. The reason for the large heatsinks is they are dimming large amounts of power. In a commercial bldg, a ceiling of lights is a lot more power than the 600W of light the usual residential dimmier is rated for.
And it should be said that incandescent lights are very inefficient to begin with. The halogen bulbs are the most efficient of the common incandescents, but they can't be dimmed without shortening their life.
Someone needs to point all these questions to the authoritive website for this, Don Klipstein's lighting website.
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.
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!!
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.
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).
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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.
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.
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.
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Dave Platt AE6EO
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