What is more efficient, a 60 watt bulb or a 100 watt bulb dimmed to the same lumens as the 60 watt puts out?

Answer 1

A 60 watt bulb on its own obviously uses less current to operate: (Power/Voltage=Current)
60W/120V=.5A
100W/120V=.83A

As you can see the 100W bulb uses more amperage than the 60W if there is no dimmer. However if we put in a dimmer and look at it like a potentiometer, then substitute the 60 W bulb for the 100W, then our full circuit use is now 100W, 120V, and .83A. The difference is that now 72V and 60W is dropped across the bulb, and 48V and 40W is dropped across the dimmer. Our current draw remains the same and total wattage or power used is the same. Therefore no efficiency is gained.
It's Ohm'sLaws in action!

Answer 2

I think the 60 watt bulb would be more efficient. The filiment would have a smaller surface area, so to put out the 60 Watts of power, it has to be hotter. A hotter filament means more of the power leaving is light in the visible range. A 100 watt bulb could put out the same lumens as the 60 watt, but it would do so at a lower temperature. So more energy would be lost in the infra-red region.

Answer 3

The 60 watt bulb running at 60 W will be far more efficient! Period.

Reason:
The efficiency of the bulb increases exponentially with increases voltage and vice versa. The lifetime will decrease exponentially as well with voltage, but that's another matter.

Now, let's assume you have a 60 W, 120 V bulb. It will last for 1000 hours and produce 850 lumen. Therefore, the efficiency is 14.17 lm/W.
Your 100 W bulb will produce 1700 lumen and last for 1000 hours. Its efficiency is 17 lm/W.

If you dim your 100 W lamp to 60 W, it will produce 491 lumen and last for 118508 hours. That's 8.17 lm/W.

If you compare 8.17 to 14.17, you will notice that your dimmed down 100 W lamp is 58 % as efficient as your 60 W bulb is.

I made a screen dump from my bulb-drive calculator, which I have developed. You can find it here:
http://greenengineering.se/yahooanswer.png

Kind regards
Andreas Vinnberg, electrical engineering student at Chalmers University of Technology

Answer 4

I agree with some one who said a dimmer switch would burn off some wattage.
To use 100 watt bulb to put out 60 watts. The dimmer switch would use 17.459671 watts. That calculated wattage is 77.459664 watts.
The 60 watt bulb has no added watt user so it still 60 watt..
I say the 60 watt is more efficient.

Answer 5

Depends. Are we talking flourescent or incandescent? A 100 W incandescent may be able to operate at the same lumens as 60W bulb but not necessarily more efficient. A 100W flourescent may not turn on at all. The wattage ratings generally are indicators of efficient running power also given factors as filament.

Answer 6

THe output lumens from different voltages when equalized from a light bulb will use EXACTLY the same wattage......
The 100W bulb will be more efficient at 60W as it will last almost indefinitely as the heat output is less at 60W than 100W.
Source: Electrical Engineer with 40+ years experience

Answer 7

60 watts since it will cost you alot less on the electric bill
you need to watch those wattage scales but flaurecent bulbs that fit into these kinds of sockets are 13 watts

Answer 8

The 60W bulb is more efficient. Both filament's resistance will increase as their temperature increases. The 100W bulb will have the lower resistance with 120V applied. That resistance will be even less as it is dimmed, therefore the power consumed will be considerably more than the 60W bulb.

Answer 9

The 60 watt bulb.
Because the dimmer will burn off quite a few watts itself.

Answer 10

i know 60 watt is efficent.
energy uesd by 60 watt< energy used by 100 watt
for the same output