Not as much energy as an incandescent bulb wastes to heat. The average incandescent bulb uses 60 watts. An equivalent compact fluorescent lamp uses about 14 watts. A Macbook with adapter uses 16.6 watts when idling with display on. A current technology LED bulb that is equivalent to a 70 watt incandescent uses 9 watts (although the light won't behave the same way as CFL or incandescent light, so depends on the application). The amount of power loss in the DC conversion is pretty minimal, compared to the potential energy savings of using LEDs instead of CFL, that is of course assuming they can make the technology better within the next few years.
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Not as much energy as an incandescent bulb wastes to heat. The average incandescent bulb uses 60 watts. An equivalent compact fluorescent lamp uses about 14 watts. A Macbook with adapter uses 16.6 watts when idling with display on. A current technology LED bulb that is equivalent to a 70 watt incandescent uses 9 watts (although the light won't behave the same way as CFL or incandescent light, so depends on the application). The amount of power loss in the DC conversion is pretty minimal, compared to the potential energy savings of using LEDs instead of CFL, that is of course assuming they can make the technology better within the next few years.
Sources:
http://www.apple.com/environment/resources/specs.html
http://www.treehugger.com/files/2007/02/led_bulb_replac.php
http://en.wikipedia.org/wiki/Compact_fluorescent_lamp