When I was living in New York, my landlord used to reprimand me on a regular basis for leaving the light on in the stairwell at night or when I left the house in the morning. She would track me down monthly and tell me the cost of her electric bill (which she graciously paid) and attribute it to the single CFL bulb in the hallway.
My landlord was a somewhat simple, somewhat disillusioned older lady, and I always wrote this theory off as a curmudgeon's rant, though I did try to remember to turn the light off when I noticed it on. I suspect the other two tenants in the building made less of an effort, as the light was always blazing when I came home at night.
It got me thinking though, exactly how much energy is saved by turning off the lights? Or by using energy efficient bulbs?
The answer is somewhat complicated. If you want to calculate financial impact, have a look at the energy rating on the bulbs you buy. If a bulb is 40 watts, and is left on for one hour, it will use 0.04 kWh. Take a look at your energy bill to see what you're paying per kWh. If you pay 10 cents per kWh, then you're saving $0.004 by turning that 40 watt bulb off for one hour.
The type of bulb you buy can, as it turns out, have a huge impact on your energy costs. Here's a breakdown of four basic bulb types:
These are the old school kind your mom bought at the supermarket in the 90s. These give off 90% of their energy as heat, and only 10% as light. They should always be turned off when not in use, as they are pretty inefficient, and can also affect the temperature of your home. I actually try to stay away from these, because though their sticker price is cheaper than CFLs, they will cost you more money in the long run.
These are the kind, often seen in renovated New York apartments, that go into a socket and lay flush with the ceiling. These are more efficient than incandescent bulbs, but less efficient than CFLs or LEDs. They use the same technology as incandecents, and should be switched off when they're not in use.
The sexy spiraly kind that became more mainstream a decade or so back. These are very efficient, and will definitely give you cost savings on your energy bill and have a much longer life than an incandescent bulb. But because they require some energy to turn on and warm up, and because frequent turning on and off can shorten their lifespan, the rule of thumb on these is:
- If you'll be out of the room for more than 15 minutes, turn it off
- If you'll be out of the room for less than 15 minutes, leave it on
The most efficient option, though the most expensive upfront, turning LEDs on and off has no effect on their lifespan.
Looking at LED, CFL, and Halogen apples-to-apples LED are absolutely the most efficient and cost-effective in the long run.
So there you have it. In summary, turn lights off EVERY time you leave the house, almost always when you leave a room, buy LEDs if you can afford them, or at the very least CFLs.