# What’s the most energy-efficient kind of light?

##### Grist, March 30, 2015

Q. Does it save energy to burn candles instead of running an eco-bulb? I currently have one 18W compact fluorescent in my lounge. Please don’t say this is a burning question.

Dave C.
Dunedin

A. Dearest Dave,

To answer your question, we must turn to math (and a little conjecture). Let’s start with your 18W CFL bulb, already a respectable choice in the energy efficiency department. And let’s say we’re talking about two hours per night spent kicking back in your lounge. Using this handy formula from the Department of Energy, we can determine that shining that one bulb will use .036 kilowatt-hours of electricity per evening.

Now we need to figure out how much carbon is required to gin up those .036 kWh. This will depend on where your electricity comes from. Dave, you didn’t specify which Dunedin you call home, but I’m going to assume Florida (if it’s the New Zealand one, all bets are off, and Bob’s your uncle). Most of Florida’s juice comes from oranges (sorry!), followed by natural gas and coal. Again, the Department of Energy helps us move forward by reporting that natural gas creates 1.22 pounds of carbon dioxide per kWh; coal emits 2.08 pounds per kWh.

Still with me? Okay, then now we know that your two-hour nightly reading sessions create .044 pounds of carbon (if your power comes from natural gas) or .075 pounds of carbon (if coal). To put this one CFL in the proper context, know that the average American uses 10,908 kWh of electricity every year.