Loony Question for Today

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I don't see how that can be, 40 W is 40 W.

15-20%. How can that be, 40 W is 40 W.

Ahem, 40 W is 40 W.

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How about dimmable LED lamps, three 20 W lamps will last much longer and provide much more visible light.

?-)

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Geez. Did you do anything to validate the junk on those two sites? Tungsten photofloods at 3200 k and 3400 k have been available for over 50 years. I can buy halogen lamps with operating temperatures as high as

5700 k, for my car even. Take a look at Plank's law for energy distribution and Wein's law for spectral peak.

?-)

You will still have a heat dissipation problem, LEDs can barely take 400 = k though the lumens per watt is good.

?-)

=A0 =A0 =A0...Jim Thompson

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If you are up to some really craft-y stuff you could add non-shorted windings to the rotor to power the LEDs.

?-)

They spin from local wind as well as thermal driven flows. Either way they extract warm air from the attic.

Well, the 40W Incandescent obviously, because it is less efficient.

So you want to upgrade three 450 lm sources with three 750 lm sources.

So you are suggesting using three 240 lm sources instead, which does not make much sense. Thus, the number of lamps would have to be doubled or tripled, i.e. a new light fixture would be required.

It should be noted that "white" 6500-7000 K LEDs have a strong narrow blue spectral line and some broadband yellow and red emission, not very compatible with existing incandescent light bulbs in the room.

Bits of them do:

Best regards, Spehro Pefhany

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Tungsten melts at about 3700K, and boils at about 5800. Non-halogen photofloods had very short lives--like 20 hours--and darkened very significantly by about 10 hours. (I used them back in the 1970s when I worked in a camera store.) Halogen ones last longer, because the high gas pressure inside reduces filament evaporation.

I invite you to investigate the difference between colour temperature and thermodynamic temperature. The emissivity of hot tungsten is slightly lower in the IR than in the visible, so its colour temperature is about 100K higher than its thermodynamic temperature, but the actual filament doesn't get above 3300K.

Higher colour temperatures are obtained by using blue filters, i.e. by absorbing a lot of the red and yellow. Not how you get

If there were any solid objects that could stand 5700K, incandescents would win the luminous efficacy contest, and the greenies would have to prop up their shaky self-worth by disapproving of us for something else.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

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=A0 =A0 =A0 =A0 =A0...Jim Thompson

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=A0 =A0 =A0 =A0...Jim Thompson

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Wrong. The high gas pressure inside has no effect on the partial pressure of tungsten. What the halogen atoms in the gas do is scavenge the tungsten that condenses on the inside of the bulb, by converting it to a volatile tungsten-halogen compound, which then circulates in the gas until it gets close to the filament, which is hot enough to decompose the tungsten halide.

The scavenged tungsten deposits back on the filament and the freed up halogen atoms head back to the inside of the bulb to repeat the cycle.

-- Bill Sloman, Nijmegen

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=A0 =A0 =A0 =A0 =A0...Jim Thompson

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=A0 =A0 =A0 =A0...Jim Thompson

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as far as I understand it the is some magic with the halogen preventing the evaporeted tungsten from sticking to the glass and instead redepositing back on to in the filamement as long as the lamp is >250C, if there was a way to make sure it redeposited evenly they would last forever

supposedly dimming halogens will lower the temperature so much that the cycle doesn't work, so if you don't run them at full power now and then they won't last as long and the glass will darken

-Lasse

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Not so much "not sticking" to the glass as sublimating back off as fast as it "sticks".

The ends of the filament are cooler (the filament mount is a heat sink) so more deposits at the ends than the middle, where it's sublimating more.

True. Several hours at full brightness will restore them.

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Yes, the tungsten-halogen cycle. As metal evaporates off the filament, it combines with the halogen gas in the tube instead ofdepositing on the quartz bulb. When the tungsten-halogen molecules come in contact with the hot filament, the bonds are broken, the metal is redeposited. If the bulb is run at lower temperatures, then the redeposit doesn't happen, and the bulb darkens are fails early. The final failure mode is that the supports for the bulb are also hot enough to break the bonds, and so some of the metal gets deposited there instead of on the filament, so the filament eventually wears out.

There are shot loads of LED lamps in all colors. If you don't like white, then warm white. If these aren't bright enough then there are others, all the way to 20 watt flood lamps.

Don't be a wanker.

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Interesting proposition. The tungsten-halogen compounds don't condense on the filament, any more than they condense on the - much cooler - quartz envelope. In fact they hit the filament (like every other molecule whizzing around inside the quartz envelope) and occasionally decompose, leaving an atom of tungsten on the surface and releasing the halogen (bromine or iodine).

A tungsten halogen molecule has an equal change of hitting any part of the filament, and it's never going to stick (as a tungsten halogen molecule). The chance that it might decompose when it hits would seem to be higher at the hottest points on the filament, rather than the reverse.

The difference in the rate of decomposition with temperature would have to exactly match the difference in the rate of evaporation with temperature to give perfect restoration, so krw has a point, even if his detailed reasoning is defective.

-- Bill Sloman, Nijmegen

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This doesn't sound quite right. If the filament is incandescent, it's going to be hot enough to break up a tungsten-halogen molecule that hits it. My guess would be that the dimmed lamp would have the quartz bulb running cooler than the 250C that's needed for the iodine and bromine to scavenge the condensed tungsten off the inside of the bulb.

-- Bill Sloman, Nijmegen

Could you please give a link to lamp with E14 base producing at least

400 lm or one with E27 base with at least 700 lm and with Ra > 90 (in order to be a direct replacement for 40 W E14 or 60 W E27 bulbs).

If such lamps do not exist, how about at least Ra > 80 ?

I have nothing against truly white light, I use about a dozen T8 fluorescent 18 W/940 and /965 tubes (Ra >90, with 4000 K or 6500 colour temperature) for indirect lighting.

10-20 W LED lamps tend to be quite exotic with fan or liquid cooling and Ra in the low 70's :-)

Have a nice day, sir.

I have 25W-equivalent LED "bulbs" out in the front entry court lights... you can't tell them from incandescent. ...Jim Thompson

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