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Lumen Output of Incandescent Bulbs

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.

--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.
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Jeff Wisnia
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"Jeff Wisnia"

** The main reason is the filament runs a few percent hotter in the 150 watt bulb.

See this under: " Voltage, Light Output and Lifetime" :

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....... Phil

Reply to
Phil Allison

There are some economies of scale for higher wattage (and especially often higher current) filaments:

  1. A thicker filament takes longer to suffer from evaporation to point of failure than a thinner one does, at a given filament temperature. This means that for equal life expectancy, a thicker filament is operated at a slightly higher temperature, which slightly increases the percentage of its radiation being visible light rather than infrared.
  2. When lamp wattage increases and lamp cost increases less (or not at all, as is often the case up to 100 watts for 120V lamps), the percentage of bottom line cost being from power consumption increases and the percentage of bottom line cost being from lamp cost (including any labor for lamp replacement) decreases. This favors making higher wattage lamps more efficient to improve energy efficiency since energy cost matters more there, and lower wattage lamps lasting longer since lamp replacement cost matters more there.
  3. In the case of gas-filled incandescent lamps, making the filament thicker makes the "boundary layer" of filament-heated gas around the filament accordingly thicker, though not necessarily proportionately. This means that with a thicker filament, temperature gradient in the gas immediately surrounding the filament is less than it is with a thinner filament. This means that with a thicker filament, heat conduction by the gas per unit area of filament is decreased when the filament is thicker.

==================================================

With efficiency advantages specifically of thicker filaments, would lower voltage incandescent lamps be more efficient than higher voltage ones of same wattage and life expectancy? This is largely true until the filament gets so short and fat that heat conduction through the ends of the filament gets to be a major loss. Among incandescent lamps of equal life expectancy and specified wattage, efficiency as a function of design voltage tends to be maximized when:

For wattages of a fraction of a watt - design voltage is around/ballpark

5-6 volts, the filament is singly coiled, and the bulb has a vacuum.

For wattages of a few watts - design voltage is around/ballpark 6 volts, the filament is singly coiled, and the bulb is gas-filled.

For wattages in the 10-100 watt range - design voltage is around/ballpark

12 volts, the filament is singly coiled, and the bulb is gas-filled.

If the lamp is designed for a much higher voltage, then if the design current is still high enough to be better with gas than with a vacuum (rough ballpark near/over .25 amp) and a gas fill is used, then it helps to make the filament doubly coiled.

For wattages of a few hundred watts to kilowatt ballpark - design voltage is a few dozen volts, the filament is coiled-coil, and the bulb is gas-filled.

- Don Klipstein ( snipped-for-privacy@misty.com)

Reply to
Don Klipstein

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That doesn't apply here Phil, so you're wrong.

And I see you still quote Wikipedia (even though they're right in this instance).

--
Linux Registered User # 302622
Reply to
John Tserkezis

"John Tserkezis =

Criminally INSANE FUCKWIT "

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** It absolutely applies.

Now FUCK the HELL OFF

- you stinking, autistic, crimina pile of sub human excrement.

....... Phil

Reply to
Phil Allison

Thanks from here in Red Sox Nation, Don.

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.
Reply to
Jeff Wisnia

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