LED lighting electricity useage

[Ixodes]

OK, this is probably a dumb question but...

How does electric usage work for my adjustable 120W LED light? More specifically, if I have my fixture set at ~40%, is this 120W fixture (theoretically) using 48W, and if I have my fixture set at 100%, is it still using the same amount of electricity as a 120W metal halide bulb, even though the bulb is burning as hot as a little sun? I understand the difference in efficiencies between LEDs and heat-wasting incandescent bulbs, and I don't actually have real 'output' measures for my LED fixture so the emitted light might be the same, but for whatever reason, this discrepancy always leaves me feeling a little confused! :debi:

 

[slief]

OK, this is probably a dumb question but...

How does electric usage work for my adjustable 120W LED light? More specifically, if I have my fixture set at ~40%, is this 120W fixture (theoretically) using 48W, and if I have my fixture set at 100%, is it still using the same amount of electricity as a 120W metal halide bulb, even though the bulb is burning as hot as a little sun? :debi:

Watts are watts. You are understanding things correctly. A 120 watt fixture will use about 120 watts at 100% and 60 watts at 50%.

 

[alton]

Don't forget about the ballast/driver factor, get a cheap watt meter

 

[firebirdude]

Watts are watts. You are understanding things correctly. A 120 watt fixture will use about 120 watts at 100% and 60 watts at 50%.

Watts are certainly watts. But I would disagree that there's some linear relationship between a nearly arbitrarily marked pot setting and true wattage consumed. Having some dial turned "half way" may not actually equal 50% of wattage consumed. It's just where the manufacturer tightened the knob to the pot or marked their numbers on the chassis. And secondly, the more wattage in, the more lost to heat. It's not a linear relationship. Efficiency will decrease as light output increases. So having the fixture adjusted to exactly 50% output likely uses less than 50% of total rated power.

OP, if you really want to know, buy a kill-a-watt meter for ~$18 and know exactly the power consumption of any and everything in your house.