[artdutra04]

Originally Posted by Ether

did you mean 2,000 hours?

Four-pack for $1.20 = $0.30 each

Here's my source for the figures I chose: http://www.amazon.com/WATTS-LIGHT-FR.../dp/B000ST9AMM

Using numbers for cheaper incandescent bulbs with 1/10 the life and 1/6 the price of the one I quoted only benefits the LED replacement case.

Originally Posted by Ether

Areas served by nuclear power plants pay as little as $0.015 off-peak.

The prices I chose were listed on the Department of Energy website: http://www.eia.doe.gov/electricity/epm/table5_6_b.html

Prices of $0.015/kWh would be great if the US got 80% of their electricity from nuclear plants like France does, but given paranoia over nuclear power plants (there has still yet to be a single confirmed death or case of cancer from Three Mile Island) and a lack of a long-term nuclear waste disposal/processing/storage facility (like Yucca Mountain proposal), we're going to be stuck with much higher average electricity prices for some time, probably until nuclear fusion research yields a commercially viable solution (last I've seen, Chinese scientists have been able to sustain a 10 million degree Celsius fusion reaction for 400 seconds, and 100 million degree Celsius reaction for 60 seconds).

Originally Posted by Ether

You are ignoring the value of the heat emitted by the incandescent. In colder climates, this is not waste heat. It helps heat the house. You have to figure in the price of the heating fuel you saved.

But in the summer, your air conditioning has to fight the heat generated by incandescent bulbs. I've seen prior calculations (can't seem to find the link now) that show from a heating/cooling issue between incandescent and CFL bulbs is a wash for most of the US. If I can find the link, I'll share it.

Originally Posted by Ether

This seems unrealistic as an average, unless you are suggesting replacing only high-use bulbs with LED.

I chose eight hours per day as an average value for most lights in "busy" areas of a house/apartment.

I was considering solving these equations as a function of the hours per day of operation, but then I realized that the only difference this has is to shrink or widen the time bands. The ratio of break even point relative to the entire life of the bulb remains the same. The only way the hours or operation per year would affect the break even point relative to the total life of the bulb would be if degradation of the bulb over time occured. AFAIK this doesn't happen, so that's why I chose a fixed value (eight hours per day) to simplify calculations.

Originally Posted by EricH

Ether, if I'm not mistaken, Art was doing a simplified version, similar to what an engineering economics professor might do as an in-class exercise. He also neglected inflation. As a matter of fact, as soon as I started reading the setup, I remembered a class I was in last spring, namely, Engineering Economics. Build one transmission line or 2, based on X cost/line and Y capacity--but where are the material/transportation costs?

It's somewhat simplified, but the annual worth method is used to compare investing in an idea relative to investing in the status quo. Since inflation would affect both equally, it cancels out of these equations.

However, factoring in inflation is necessary if you want to calculate the present or future value of the savings (annual payment).