# Light AC versus DC

Discussion in 'General Electronics Chat' started by electronewb, Oct 22, 2012.

1. ### electronewb Thread Starter Member

Apr 24, 2012
260
3
Another strange question. Someone at work mentioned that a 35W DC lamp is more powerful than a 35W AC lamp!!!! I thought that power is power!!! One lamp is fed by 120VAC and the other is fed by a 14VDC battery!!

2. ### wmodavis Distinguished Member

Oct 23, 2010
739
151
Should be pretty easy to test. The two of you should work together and perform an experiment to determine which is the case. That is how science works. Theory, test.

3. ### electronewb Thread Starter Member

Apr 24, 2012
260
3
But in theory 35W=35W no matter if it AC or DC maybe what he was trying to say is the 14VDC needs less voltage than the 120VAC lamp to get the same wattage. Watt is a unit of measure just like a centimeter 1CM=1CM

4. ### crutschow Expert

Mar 14, 2008
21,415
6,136
A low voltage incandescent lamp (doesn't matter if it's AC or DC) can have a higher lumen output than a higher voltage lamp of the same power rating since a lower voltage lamp can have a thicker (lower resistance) filament for a given wattage and thus can be operated at a higher temperature without being too fragile. This gives more light output in the visible and less in the infrared. That's why many of the small halogen lamp fixtures are operated from 12VAC using a line operated transformer instead of directly from the line voltage.

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5. ### strantor AAC Fanatic!

Oct 3, 2010
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3,079
I have a 35W power resistor and it doesn't give out any light at all.

absf likes this.
6. ### mcgyvr AAC Fanatic!

Oct 15, 2009
5,394
1,194
power is power BUT
light output versus power is what all the led companies are fighting for now.
Its the great "Lumens per Watt" competition...

7. ### wmodavis Distinguished Member

Oct 23, 2010
739
151
"But in theory 35W=35W no matter if it AC or DC"

If you are comparing DC power to RMS AC power, you are correct.

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