Lumen Output of Incandescent Bulbs
- From: Jeff Wisnia <jwisnia@xxxxxxxxxxxxxx>
- Date: Fri, 03 Aug 2007 23:47:33 -0400
About ten years ago I installed "touch dimmers" inside four metal bodied table lamps in our home and replaced the "three way" 50-100-150 watt incandescent bulbs they'd been using with 150 watt bulbs.
Some time later I bought some "Y" bulb adaptors and started using two 75 watt bulbs in place of the 150 watt bulbs, for two reasons; First, the 150 watt bulbs cost about twice as much as a pair of 75 watt bulbs of the same brand and series, and when one 75 watter burned out, I could still get some light to see by until I put in a new bulb.
Two times 75 equals 150, right?
I mentioned that on another newsgroup last week while explaining how I'd also installed 2 amp fast blow fuses in those lamps to protect the dimmers because occasionally when a bulb expired it did so in a blaze of glory with one of those "tungsten arcs" which blew the tracks right off the dimmer's printed circuit boards. Those fuses fixed the problem, they blow (only 10 cents each.), but the dimmers live on. (The I^2*t blowing rating for those fuses is slightly less than the max I^2*t for the triacs used in the dimmers)
I got a reply asking me if I'd thought about the difference in light output between a pair of 75 watt bulbs (1190*2 = 2380 lumens) and a single 150 watt bulb of the same brand and type (2850 lumens). That's 20 percent more light output from the 150 watt bulb when running at full voltage. I hadn't, and put a 150 watt bulb in one of a pair of lamps and compared it's brightness to the two 75 watt bulbs in the other lamp. The difference was so noticable that I put 150 watt bulbs back in the other three lamps.
Which brings me to the subject question....
What are the reasons for the differences in lumens per watt output between the 75 and 150 watt bulbs? All I can think of is:
The filament of the 150 watt bulb is further away from its base, so there's a longer thermal path along the filament supports to suck heat away from the filament, and because it's further away from the filament, the base obscures and absorbs a smaller percentage of the radiated visible light.
Can those be the reasons?
Thanks guys,
Jeff
PS While in the store buying those new 150 watt bulbs I noticed that the "full on" rated light output from a "three way" 50-100-150 watt bulb was considerably less than that for a simple 150 watt bulb. The "three way" bulb was physically the same size as the 150 watter which sort of makes my speculations above sound not so good to me anymore. <G>
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.
.
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