M Q wrote:



Jeff Wisnia wrote:

...

Well, I followed through and bought some 150 watt bulbs yesterday.
While I was at the store looking at the lumen ratings of frosted
incandescents I noticed that the 150 watt output of a "three way"
50-100-150 watt bulb was also considerably lower than that of the
plain 150 watter.

Yes, a "3-way" is just a 50 W and a 100 W in the same globe.


I replaced the "Y" adaptor and its two 75 watt bulbs in just one of
our two living room table lamps with a 150 watt bulb.

the results were pretty dramatic, the lamp with the 150 watt bulb was
noticably brighter, so I put a 150 watter in the other one too.

Now I need someone to understand why the single 150 watt incandescent
puts out 20 percent more lumens than the pair of 75 watt bulbs. (Are
you reading Don Klipstein?) I'm guessing it might have something to do
with more thermal energy being tossed away through four filament
supports than through two, or something like that.


I can give you a partial answer. The filaments in higher wattage
bulbs are designed to run at a higher temperature. At the higher
temperatures, more of the radiated energy is in the visible light
portion of the spectrum (see http://en.wikipedia.org/wiki/Black_body )
(however still only around 3-5%). Why don't we just run all
bulbs hotter? That dramatically decreases the lifetime of the
filament. Why can we get away with running higher wattage
filaments hooter than lower wattage ones? That's the part that I
don't know.


Maybe another reason is because the bases of both bulbs are the same
diameter but the 75 watt bulb is physically smaller than the 150 watt
one. That puts its filament closer to its the base which makes the base
obscures a larger solid angle in the total sphere of radiation, thus
blocking a greater percentage of the visible light?

Jeff

snipped

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10^12 furlongs per fortnight.