Similar to this question (except that's about cars), if I can buy more efficient light bulbs than the ones I'm using right now, should I? Or is it better to wait until my current light bulbs expire, based on the environmental cost of creating new light bulbs?
Consider the pay back time. high efficiency lights are expensive. Expense is, at least in part, a measure of the resources used to make it.*
Replacing the fixtures in the kitchen where the lights are on 8-10 hours a day is probably a good idea.
Replacing the lights in the hall closet that runs 20 minutes a week is not.
Example: Our kitchen has two T8 fluorescent fixtures, two Edison base potlights and 1 two bulb entrance light.
The main lights in the kitchen are on about 8 hours a day. The entry way, maybe 1 hour a day, the potlights maybe 1 hour a month.
Suppose that LED lights would be 40% efficient instead of 30%. 4 x 35 watts becomes 3 * 35 = 105 watts instead of 140. 35 W * 8 hr = 280 or about 100 kWh/year. If my power is 15 c/kWh that would be about $15 per year. Kits to replace bulb and transformer are slightly more expensive than bulbs that use the existing transformer, but are not as efficient. Call it $15 per bulb. So my payout is 4 years.
The entry way light is on 1 hour a day, and was equiped with 40W tungsten bulbs. The replacement LED bulbs are now about $2.50 each and use 7 watts each. I save 33 w * 365 hours = about 12 kWh/year. That's about $1.80/year. Pays for itself in something like 3 years.
The potlights had 60w bulbs in them. They are on 12 hours a year. That's 720 watt hours or not quite a kWh. So they are costing me about a dime a year.
I replaced them anyway, and am trying to get into the habit of using them instead of the main lights.
Replace the lights in the high use area, saving the bulbs for reuse in low use areas. We have replaced all lights in our rooms in our house with screw in fluorescents except for the furnace room, one stairwell, and a few closets, and the front porch. No one makes a high efficiency light that works at -40. I think we have 5 tungsten bulbs still in stock. Once they are used up we will replace them with fluorescents or LED bulbs.
* Using expense as a measure of sustainability is a first approximation only. A better approximation is wholesale cost of commodity equivalent. This helps you filter out most of the marketing, advertising costs.
I'd replace working incandescent bulbs with LEDs. We did this in just one heavily used room (with about 300 watts worth of incandescent bulbs) and saw our electric bill go down. My husband did not like the light from CFLs in our "office." We ended up replacing various CFLs also except in cases where comparable LEDs were not readily available. (For instance, one of our light fixtures has five small CFLs that burn only 7 watts apiece. We could find no replacement.) At least in rural Iowa, LEDs seem to be less expensive all the time (i.e. under $2 as opposed to $8 or $9 a few years ago) and use about 11 watts to produce more light than a 75 watt incandescent. In short, our LEDs use half as much energy as our CFLs were using. On a nationwide scale, this is a huge improvement. Therefore, I have also switched CFL bulbs to LEDs as they became available. I wanted to support the technology and help prices come down.