Light output of dimmed lamps

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Can anybody point me to some information about how the light output of incandescent and halogen lamps varies as they are dimmed? I'd like to compare the efficiency of a high-wattage bulb when dimmed to lower wattage bulbs operated full-on.
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The only way I can think to really know is use a clamp on amp meter or Kill-A -Watt since all bulbs are a bit different and need a minimum starting voltage. A 100 watt bulb dimmed to 60 watts should put out less light than a 60 watt will. A Kill-A -Watt meter is good to have around
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There was also a thread recently about dimming halogen lights. they burn out faster IIRC
More that you need to know about dimmers here: http://www.epanorama.net/documents/lights/lightdimmer.html
Good info here: http://www.clarkpublicutilities.com/Residential/TheEnergyAdviser/Archives2001/6-01-4 You are correct that an old rheostat dimmer that uses a resistance coil to divert some of the energy passing through it does not produce much energy savings. The dimmers literally detour some of the light energy to a component in the switch that converts the energy to heat. The lights are dimmer, but the energy savings is minimal.
When shopping for a new dimmer to replace a rheostat model, make sure to specify an electronic dimmer. Electronic dimmers use a circuitry called TRIAC to control voltage to the light bulbs. TRIACs trim the voltage to the bulb without creating heat, and effectively reduce the energy use while only losing about one percent of the savings to operate the dimmer circuit. A good TRIAC dimmer will reduce the light output over a broad range, and in turn trim the energy use.
However, the ratio of light output to dimmer setting is not equal to an overall reduction in wattage. In other words, a 100-watt bulb dimmed to the equivalent light output of a 60-watt bulb actually draws 70 watts through the electronic dimmer. If you always use the fixture in a dimmed position, you'd be better off reducing the wattage with new bulbs instead of using a dimmer.
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In a related question---- If I leave the dimmer in the lowest position where the light is (looks) turned off, is it still drawing power?
D.

http://www.clarkpublicutilities.com/Residential/TheEnergyAdviser/Archives2001/6-01-4
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Mine has a "click" for the off position. Based on the following, I think it still takes some power when turned down past visible light.

Perhaps someone knows for sure.
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wrote:

A small enough amount of power won't be able to heat the filament to a high enough temperature for it to emit visible light. It could still be emitting some infrared.

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Pawlowski wrote:

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A couple of the many details this thead needs:
If you choose to continue using incandescent bulbs, use one high-wattage bulb in place of multiple low-wattage bulbs wherever possible. A 100-watt light bulb produces as much light as two 60-watt bulbs.
Wattage is often used as a substitute for the brightness of a lamp, but it is a poor substitute. Usually, a 100 Watt lamp will burn brighter than a 50 Watt lamp. But just because the larger lamp is using twice as much power, doesn't mean it is putting out twice as much light. It could be that the 100 Watt lamp is very inefficient at turning electricity into light, and the 50 Watt lamp is much more efficient.
Reducing the voltage applied to a light bulb will reduce the filament temperature, resulting in a dramatic increase in life expectancy. One device sold to do this is an ordinary silicon diode built into a cap that is made to stick to the base of a light bulb. A diode lets current through in only one direction, causing the bulb to get power only 50 percent of the time if it is operated on AC. This effectively reduces the applied voltage by about 30 percent. (Reducing the voltage to its original value times the square root of .5 results in the same power consumption as applying full voltage half the time.) The life expectancy is increased very dramatically. However, the power consumption is reduced by about 40 percent (not 50 since the cooler filament has less resistance) and light output is reduced by reduced by about 70 percent (cooler filaments are less efficient at radiating visible light).
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I would challenge you to find one (for residential use) that ISN'T an electronic (triac) dimmer! They've been that way for decades.
The only dimmers that aren't are the variac (variable transformer) dimmers which are very large affairs which I've never seen in residential use. They are, BTW, superior in terms of putting out a normal AC waveform, not the weird stuff a triac dimmer puts out. As for a rheostatic (resistance) dimmer, I've never seen one outside of an old theatre stage lighting board.
(Technically the knob or slider you move on a triac dimmer is a variable resistance but it's properly called a potentiometer as it is handling only a control voltage not the actual power throughput which is what the term rheostat implies.)
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Steve Kraus wrote:

I did, once....But it was quite a residence, the home of John Hayes Hammond, a prolific inventor obviously knowlegable in the electrical technologies of his era.
They were in round housings designed for wall mounting, with a good sized knob on the end to crank the sliding tap around with. IIRC they were about 7 inches in diameter and stuck out from the wall about 5 or 6 inches.
A fun place to visit indeed:
http://www.hammondcastle.org /
Happy Holidays,
Jeff
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On Sat, 24 Dec 2005 02:20:09 GMT, Steve Kraus

You beat me to the punch. I was going to say the same. Except for maybe wacko millionaires, I don't think anyone had dimmers in their home until they had transistorized** dimmers. Others were too big to fit in the regular box, and too expensive too.. **I count any semiconductor as a transistor, including triacs and diodes
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FWIW
A strange thing... About 10 years ago, in a modest duplex (nice suburb,) was a 3" knob on a device in a 4" square box. When we pulled it from the wall it was an auto-transformer dimmer!
Just when you think you've seen it all...
RickR
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Dimmed bulbs burn out faster? :-)
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Halogen lamps do. They require a certain internal temperature of the inside glass envelope to start the halogen cycle.
http://www.goodmart.com/facts/light_bulbs/halogen_cycle.aspx
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http://www.goodmart.com/facts/light_bulbs/halogen_cycle.aspx
I don't see that there. I can imagine it could go either way. A lower temp filament will evaporate less, so the bulb might last longer. How long would it last at 10% power? At 1%? At 0.0001%? :-)

Every black body above absolute zero emits some visible light.
m Ransley wrote:

Easy, with a grease spot photometer. Move a 3x5 card with a grease spot between dimmed and undimmed bulbs until the spot disappears, when it has equal illumination on both sides and outputs are inversely proportional to the square of the distance from each bulb.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Yes it evaporates less, but far more of it ends up on the glass while when the cycle is working it just goes back to the filament. In real life it does work in such a way that the lamps do not last as long.
That said, my experience with projector bulbs is that used at half power they seem to last about the same time as full. While the older non-halogen lamps lasted a lot longer at half power. My 60W lamps by my sofa don't seem to be much effected, but the little peanut lamps under the counter last longer at full power maybe 50% longer.

Difficult to measure if true. I fear my college physics is about 40 years old now and while I am sure the answers have not changed on that one, my memory is a little weak.

That is what I would use, but there are other methods. I doubt if my spot meter could measure the light from a filament cooled to 3 K. :-)

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The way I saw it on a rather technical book (25 years ago) on this, the halogen cycle slows down less than filament evaporation does when the bulb is underpowered. This is, ideally!
However, the halogen cycle does attack the cooler ends of the filament. You don't gain much when you dim below the point at which the ends of the filament get eaten away faster than the filament gets damaged by evaporation. Yes, the halogen cycle is only a little good at protecting a filament from evaporation - the evaporation is not perfectly even and the halogen cycle is not that good at returning tungsten to the parts of the filament that need it the most. Halogen lamps last longer despite higher filament temperatures not as much from the halogen cycle but because the fill gas is at a higher pressure and because the fill gas often has premium gases such as krypton - whose larger atoms "bounce" evaporated tungsten atoms back to the filament more than argon atoms do. The small size of halogen bulbs/"capsules" makes premium fill gases more economical. Still another advantage of halogen lamps is that the small capsule size slows convection movement of the fill gas, and with the fill gas more stagnant the filament evaporates more slowly. These reasons rather than the halogen cycle are mostly why a halogen lamp lasts longer than a non-halogen one of the same filament temperature. Of course, an advantage of the halogen cycle is keepin the inside surface of the bulb clean - which becomes more necessary when the bulb has a smaller inside surface where tungsten deposit would be more concentrated and more opaque.
Sometimes when a halogen bulb is dimmed severely, things go really awry - depending on the quality of the bulb. Traces of water vapor or oxygen could be doing the opposite of what the halogen cycle is trying to do, and these bad effects do not slow down as much as the halogen cycle does when the bulb is dimmed, and the bulb needs a certain filament and bulb temperature in order for the halogen to outrun the negative effects of contaminants.

Well, a blackbody does emit some visible light at any temperature, but it appears to me that you need about 700 Kelvin to see it with a dark-adapted eye. In any case, I would think something would have to be far above body temperature to squeeze more light from a filament through your pupil onto any point of your retina than that point receives from the remainder of your retina.
- Don Klipstein ( snipped-for-privacy@misty.com)
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I've often wondered what the temperature of my '51 Chevy Carryall engine was when I noticed it was running rough and pulled into a PA Turnpike rest stop one night and opened the hood and saw the whole block glowing a dull red... 1292 F, after it ran out of water and oil? :-)
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Somehow at this hour my mind likes to pick out of Fahrenheit 1,000 degrees as dimly glowing and 1500 degrees as a medium-brightish-orangish "red-hot"/"cherry-red-hot" that has a hue more a reddish orange than really red...
1,000 F is to the nearest degree 811 Kelvin. I think that is visible in an otherwise dark area with some dark adaptation, not requiring full dark adaptation. I would expect seeing color of this, an orangish shade of dim red. Closer to 700 Kelvin, my experience is that light output is so low as to be only/mainly seen by human eyes through scotopic vision despite this light having wavelengths less favorable to scotopic vision - so the color at temperature that low gets more grayish or brownish-gray.
811 Kelvin blackbody has surface brightness of about 1.2E-6 candela per square centimeter, and color close to CIE 1931 x=.68 y=.32 z=0, or dominant wavelength (roughly but not perfectly exactly a specification of hue) about 614-615 nm (orangish orange-red).
I wonder how you determined 1292 F... That's 973 Kelvin. Blackbody achieves about 1.4E-4 candela per square centimeter, and chromaticity (using 1931 CIE system) is about x=.657, y=.341, z=.002, which has dominant wavelength about 608 nm - usually seen more as redish orange than orangish red, but usually called "red-hot" since 1.4E-4 candela per square centimeter from an ideal emitting surface is only about 4.4 lux, which is dimmer than most normal room illumination in homes.
1500 F is about 1089 Kelvin - blackbody achieves about .00186 candela per square centimeter, from ideal radiator or about 58 lux, a "brighter red-hot" or "good-and-hot-cherry-red-hot". I suspect such terms could be used to about 1600 F, or 1144 Kelvin (achieving .0053 candela per square centimeter, about 166 lux from an ideal radiator). As for color: 1500F / 1089 K has 1935 CIE system chromaticity of x=.6402, y=.3553, z=.0045, dominant wavelength close to 604 nm - usually considered orange or a slightly reddish shade of orange. 1600F /1144 K gets about x=.632 y=.362 z=.006, which has dominant wavelength about 602 nm, pretty much plain orange to maybe slightly reddish. Achieving a more-highly-arguably non-reddish orange (dominant wavelength by most of various means of 600 nm) requires from a blackbody 1250-1255 or so Kelvin, about 980 C, about 1795-1800 F. Heck, I believe that can get a little bit on the yellowish side! Oxidized copper at its melting point (1083 C, 1356 K, 1981 F) surely appears to me a rather yellowish orange, and has 1931 CIE chromaticity coordinates about x=.604, y=.382, z=.014. That is yellowish orange with dominant wavelength about 598 nm, maybe 597 nm. Compare to sodium-tinted flame with dominant wavelength 589.something, often seen as orange-yellow and sometimes more orange than yellow.
Maybe I need a vacation...
Also wondering what was the end of the story of a car whose engine block incandesced at 1292 degrees F!
- Don Klipstein ( snipped-for-privacy@misty.com)
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Why 700? One artist at The Mattress Factory in Pittsburgh uses such low light in a room that it takes about 15 minutes to become barely visible. How many W/m^2 do we need to be able to see an object with no resolution at the our most sensitive frequency? Can we see a single photon?

A 3 AM math error... 700x1.8+32.

That early SUV never ran again. Too bad. Serious Detroit Iron. The engine even had a socket for a hand crank. I was nursing it home from Ithaca NY with a slightly cracked block, feeding a slow water leak on a very cold night and the gauges didn't work and I didn't realize it was overheating until too late.
Nick
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