dimmers on bulbs ...

I was told by a lighting designer that a light dimmer can save a lot of energy. In fact his claim was that dimming an Incandescent light bulb by 5%,
can save up to 40% of the electricity consumption.
I tried to verify this claim but I could not find anything that matched even near this claim. In fact, what I read (and makes absolute sense to me) is that dimming the light, say by 50%, will only save 40% of the electricity consumption.
Does anyone know (and can justify) what the truth is? I have some basic EE knowledge and I just cant figure out how the dimming of 5% can give more than 2-3% savings, given the loss in heat etc...
Many thanks A
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:I was told by a lighting designer that a light dimmer can save a lot : of energy. : In fact his claim was that dimming an Incandescent light bulb by 5%, : can save up to 40% of the electricity : consumption. : : I tried to verify this claim but I could not find anything that : matched even near this claim. : In fact, what I read (and makes absolute sense to me) is that dimming : the light, say by 50%, : will only save 40% of the electricity consumption. : : Does anyone know (and can justify) what the truth is? : I have some basic EE knowledge and I just cant figure out how the : dimming of 5% can give more : than 2-3% savings, given the loss in heat etc... : : Many thanks : A : A drop of X% in energy consumption will result in a greater than X% reduction in light output.
Charles Perry
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AndCy wrote:

Better to install the proper sized lamp in the first place. The light output of an incandescent lamp goes down out of proportion to the decrease in power input - so you're paying more for those lumens with a dimmed lamp. Read the Wikipedia article on incandescent light bulbs, which, if no-one's hacked it, has some descriptions of the relationships between power, light, life, and efficacy.
Bill
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AndCy wrote:

I agree with Charles and Bill.
Looking at a published curve: 95% voltage 91% energy consumption (watts) 82% light output (lumens) 120% life
As Charles wrote, the light output will always fall faster than the electrical energy consumed. That is because the spectrum moves toward red. The percentage that is infrared (heat) increases. The more you dim the worse it gets.
Was the lighting designer named Roy?
Dimming makes sense if you need the maximum light level some of the time. I have not seen curves, but dimming CFLs probably does not greatly reduce the efficiency (using CFLs intended to be dimmed).
If you increase the voltage, an incandescent lamp will be more efficient (lumens/watt). That is what tungsten-halogen lamps do. They do not have the reduced life that a normal incandescent would have.
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It does, but the power consumption is so much lower to begin with that it doesn't really matter. As you dim a fluorescent lamp, power to the cathodes must be increased to keep them hot enough that they don't sputter. You also get color shift that is unfortunately more yucky rather than the pleasing atmosphere created by dimmed incandescent. In many cases though it's good enough.
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wrote:
| I was told by a lighting designer that a light dimmer can save a lot | of energy. | In fact his claim was that dimming an Incandescent light bulb by 5%, | can save up to 40% of the electricity | consumption.
If this were true, then people would be installing 10000 watt lights and dimming them down to the 1% level.
| I tried to verify this claim but I could not find anything that | matched even near this claim. | In fact, what I read (and makes absolute sense to me) is that dimming | the light, say by 50%, | will only save 40% of the electricity consumption.
The big problem with incandescent lights is that most of the energy going into them comes out in the form of heat, both as convective heat and as infra-red radiation. Light is only a minor side effect of a hot filament. The center wavelength of the radiation is in the infrared range.
When an incandescent light is dimmed, it reduces the temperature of the filament. When the temperature goes down, two things happen. One is that all the radiation level goes down. But the other thing that happens is that the wavelength gets longer and moves deeper into the infrared region. So while the total radiated energy goes down, the proportion of that energy that is in visible wavelengths also goes down. The end result is that the level of visible light reduces faster than the level of wasted radiation.
If you are using light bulbs to provide heat, then, of course, the infrared radiation is not waste.
| Does anyone know (and can justify) what the truth is? | I have some basic EE knowledge and I just cant figure out how the | dimming of 5% can give more | than 2-3% savings, given the loss in heat etc...
Dimming a light definitely reduces the electricity used. Turning off some lights would reduce the electricity used, too. The question you need to answer is which method of reduction would work better for your particular needs.
If you want the softer yellow to orange color effect of a dimmed incandescent light, then dimming can be useful. If you always want to be able to run the light at full brightness for other times when a bright white light is desired, then an adjustable dimmer is probably the way to go.
If you want to simply have less light, and keep it white, then multiple lights on separate switches might be better for you. This is the most efficient way to reduce energy usage by lights. But it can cost more to install because of the extra switches and separate wiring.
If your goal is to have white incandescent light with the least power usage then size the light to exactly what you need and don't bother with dimming.
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