LED spotlights
 

After building a new padio and getting the patio furniture. I decided to replace the two 100 Watt incandescent spotlight bulbs on the back of the house. I don't like cfls for exterior use because they take a while to warm up or don't work on cold days. So, I bought two 5 watt LED spotlight bulbs for $14 each at Costco. According to the packaging, each bulb will save us $136 per year. I am not sure that I agree with that number since my spreadsheet only calculates it at $46 per bulb per year (a 4 month payback). I really like the LEDs. They are brighter than the incandescent that were on the house and after adjusting them to point at the patio table, they don't blind us when we are looking at the person diagonally across from us. Hopefully, they will live up to their life expectancy of 10 yrs.

The amount depends on local power rates and how many hours a day they are on.

Jacob - Yeah, I understand that.

So to do the math, I take 200 Watts (two bulbs) minus 10 Watts and that leaves 190 Watts saved times 2 hours of use per day (estimated average. We use them to put the dogs out and see when they are ready to come in) times kWh/1,000 Wh. That gives me 0.38 kWh per day times 365, times $0.65 (on my bill).

I save $90 per year for both lights ($45 per light). That is equivalent to 0.1 tons CO2 per year for both lights.

I wasn't questioning your math, just saying the estimate on the box is probably using different assumptions.

My LED porch light only uses 1 watt, so, since I was constantly forgetting to turn it on at night and off in the morning anyway, now I just leave it on 24/7

It makes me happy (and surprised) that these are being sold at costco now. When I got mine I had to order them online. The idea of efficiency is perhaps finally catching on!