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You also have to make an assumption about the typical weather. The waste heat offsets heating costs in cold climates, but in hot climates, you must also burn a

You also have to make an assumption about the typical weather. The waste heat offsets heating costs in cold climates, but in hot climates, you must also burn additional electricity to pump the waste heat outside. My estimate is that a 50W bulb efficiency improvement results in a saving between 30W-70W depending on the climate. If you live in Iceland, the payback is probably never. If you live in Singapore, you will recoup the cost in months. I personally use LEDs everwhere except my bathroom during winter, where I use inefficient globe bulbs because it warms the bathroom.

mikeash 14y ago
That's an interesting point. Reminds me of when a Wisconsin city replaced all of their stoplights with LEDs, then discovered come winter that the new bulbs wouldn't melt snow like the old ones did, requiring a lot of manual cleaning to remain visible. I'm not sure how much of a difference it's likely to make, though. Houses in cold climates usually use more efficient heating systems, so the heat from a light bulb will be pretty costly by comparison. With a 50W savings, the cost for additional heating to make up for that will probably only be equivalent to about 10W of electricity, or less, depending on your setup. Air conditioning is usually pretty efficient, with efficiencies better than 10 (10W of heat removed for 1W of electricity used). So that 50W savings will still be 55W or less when taking air conditioning into account.
- jcampbell1 14y ago
  > Air conditioning is usually pretty efficient, with efficiencies better than 10 I think you are off by a factor of 3.412. The SEER rating may be 10, but that means you push 10BTUs per Watt Hour, or 2.9 WH/WH. I am also assuming that burning NatGas produces electricity about 40% efficiency delivered, and burning it at home for heat is about 80% efficient.
  - mikeash 14y ago
    My whole life is a lie! Thanks. Never thought people would actually use an efficiency rating where 1 didn't mean 1:1. Now I know better.

mikeash 14y ago

That's an interesting point. Reminds me of when a Wisconsin city replaced all of their stoplights with LEDs, then discovered come winter that the new bulbs wouldn't melt snow like the old ones did, requiring a lot of manual cleaning to remain visible. I'm not sure how much of a difference it's likely to make, though. Houses in cold climates usually use more efficient heating systems, so the heat from a light bulb will be pretty costly by comparison. With a 50W savings, the cost for additional heating to make up for that will probably only be equivalent to about 10W of electricity, or less, depending on your setup. Air conditioning is usually pretty efficient, with efficiencies better than 10 (10W of heat removed for 1W of electricity used). So that 50W savings will still be 55W or less when taking air conditioning into account.

jcampbell1 14y ago
> Air conditioning is usually pretty efficient, with efficiencies better than 10 I think you are off by a factor of 3.412. The SEER rating may be 10, but that means you push 10BTUs per Watt Hour, or 2.9 WH/WH. I am also assuming that burning NatGas produces electricity about 40% efficiency delivered, and burning it at home for heat is about 80% efficient.
- mikeash 14y ago
  My whole life is a lie! Thanks. Never thought people would actually use an efficiency rating where 1 didn't mean 1:1. Now I know better.