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Author Topic: Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?  (Read 10104 times)

Offline neilep

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Dear Bulbologists,



As a sheepy I am of course very bright. Stick me on top of a Christmas tree and ewe have yourself the best looking Chrimbo tree decoration ever !


See this 5 watt bulb ?




Nice eh ?


Why is it that two of those 5 watt bulbs are not as bright as a ten watt bulb ?..why’s that then ?

Doing the maths is confusing….......2 x 5 watt bulbs = 10 watts yes ? (US Translation service "Maths" = " Math"..sheesh !)

10 watt bulb also = 10 watts ?

Watt is going on ?  (notice the play on words there ?....that was bright of me wasn’t it?..........notice the play on words there again…good eh ?...ewe could say I have an enlightened sense of humour…………Notice the play on words there yet again eh ?...how illuminating !...notice the ..OH SHUT UP !!!)


Your  answers will make for a happy sheepy.




Hugs & Shmishes


Mwah mwah mwah mwah



Neil
That Light Bulb Looks Like A Butt Plug !
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx


 

Offline Chemistry4me

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #1 on: 05/12/2008 23:52:08 »
Perhaps the two 5 watt bulbs loses more energy as heat compared to the 10 watt bulb?
 

Offline lightarrow

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #2 on: 05/12/2008 23:52:45 »
Dear Bulbologists,

Why is it that two of those 5 watt bulbs are not as bright as a ten watt bulb ?..why’s that then ?

If the 10 watt bulb costs more than the two 5 watt bulbs, you already have the answer...
If it costs less, then throw away the 5 watt ones and buy the 10 watt only  ;)
« Last Edit: 07/12/2008 12:09:25 by lightarrow »
 

Offline Don_1

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #3 on: 06/12/2008 00:25:18 »
Try this, hold out your hands and count your fingers (& thumbs).
1; 2; 3; 4; 5; 6; 7; 8; 9; 10.

Now count back starting, of course, at ten, on one hand:
10; 9; 8; 7; 6!!!

6 minus 10 = 4???!!! yes, there's one missing.

Does that explain your problem?
 

lyner

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #4 on: 06/12/2008 18:09:26 »
The original question does not really involve a 'fair test'.
Two 5W bulbs, operating at 100V design voltage would produce virtually the same amount of light as one 10W bulb, operating at 200V design voltage.
All three bulbs would / could have filaments with the same cross sectional area and the Volts per metre of filament wire would be the same.
Your selection of bulbs don't satisfy that requirement. The higher power bulb may have a fatter / shorter filament (lower R) so it may well end up at a different surface temperature and produce comparative a light output which would be hard to predict without knowing much more about it.

I understood that the 25W, 40W,60W and 100W ratings can be expected to produce double the light output for each step. (All other things being equal, of course - but lifetime is another factor which governs the light output they are designed to have).
« Last Edit: 06/12/2008 18:12:55 by sophiecentaur »
 

Offline RD

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #5 on: 06/12/2008 18:51:07 »
Q. Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
A. Because the filaments of the two bulbs are separated by some distance the maximum brightness (intensity) of the light will be less than the case of a single bulb with twice the power.

e.g.
imagine a room lit with a single central lamp of 120 Watts, then imagine the same room lit by two 60 Watt bulbs separated by two meters.

The illumination of the room will be more even with the two 60 Watt bulbs, but with the single 120 Watt bulb the room will include an
 area of higher brightness than exists in the room when it is lit by the two 60 watt bulbs.
« Last Edit: 06/12/2008 18:55:54 by RD »
 

lyner

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #6 on: 06/12/2008 20:22:24 »
Quote
A. Because the filaments of the two bulbs are separated by some distance the maximum brightness (intensity) of the light will be less than the case of a single bulb with twice the power.

Too simplistic.
Whilst you are correct in terms of total dissipated power, the amount of radiation in the optical region (brightness) depends on the surface temperature. This depends upon the effective surface area of the filament (Stefan's law and Rayleigh Jeans).

The power dissipated by a filament depends upon the resistance (v2/R).
To get a given value of R, you can choose over a big range of lengths and thicknesses. For a high surface temperature, a low power bulb has such a small filament that it disintegrates in no time at all.they have to make them fatter so they have a lower colour temperature so they can actually survive an acceptable time.
It's a complicated situation.
 

Offline RD

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #7 on: 06/12/2008 20:43:08 »
I've just noticed Neilep's bulb is fluorescent not incandescent.
« Last Edit: 06/12/2008 20:46:17 by RD »
 

lyner

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #8 on: 06/12/2008 21:23:44 »
Owch!!!
 

Offline techmind

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #9 on: 07/12/2008 00:46:24 »
Dear Bulbologists,
...
Why is it that two of those 5 watt bulbs are not as bright as a ten watt bulb ?..why’s that then ?

Firstly, I'd ask how you measured that 2x 5W was less bright than 1x 10W.
Do the 5W and 10W bulbs use comparable technology? And same manufacturer?

While it is true that filament bulbs can trade off lifetime and mechanical robustness against efficiency (light out for given power in) by changing filament length, coiling, and cross-section ... hence why a 50W halogen is more efficient in its 12V version than its 240V version ... I doubt you'd expect to see much noticeable difference in light output between two otherwise-similar filament bulbs of NWatts and 2x (N/2) Watt bulbs.

However, if you're looking at those silly compact fluorescent "lites", then all bets are off for anything being consistent. Firstly the light-output decreases over time, so if you're comparing old (used) bulbs with new that'll cause a major discrepancy. Secondly they may have different phosphor mixes which give different colour-temperature (higher colour temp bulbs appear brighter - although the light is stark and particularly unflattering). Even if the colour-temperature is consistent, the spectral emission may differ, which may affect how bright different materials look when illuminated by the light.

Another factor is that CFLs tend to be dim when they first come on, then warm up to full brightness. Your lower power 5W bulbs may take longer to warm up.

But it's probably simply not-unreasonable that a lower-wattage CFL bulb is less efficient as the overhead of the drive control-electronics becomes a greater fraction of the whole...?

A CFL is anything but simple, so don't be surprised if simple rules don't apply.
 

lyner

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #10 on: 07/12/2008 12:27:51 »
My first point about the 'fair test' has to apply.
 

Offline DoctorBeaver

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #11 on: 07/12/2008 14:23:34 »
Quote
6 minus 10 = 4

Are you sure of that, Don?
 

Offline Don_1

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #12 on: 07/12/2008 16:41:51 »
Quote
6 minus 10 = 4

Are you sure of that, Don?

Opps, beg pardon, 10 minus 6 = 4


FOG
 

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Why Is Two 5 Watt Bulbs Not As Bright As A Ten watt Bulb ?
« Reply #12 on: 07/12/2008 16:41:51 »

 

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