Light bulbs and power savings

| Comments (6) | Misc
Mike O'Hare makes an interesting point about current efforts to convert incandescent lights to compact fluorescents (CFLs). Like many O'Hare posts, the writing is a bit hard to track, but the point is simple: any lighting system has two outputs, light and heat. The heat is typically thought of as waste and so CFLs are more efficient than incandescents in that they have a far higher light/heat ratio. If you're heating your home anyway, than that heat isn't waste, but rather it's something you want, so if you switch from incandescents to CFLs you end up heating your home some other way. Some of those ways are more efficient than others is,1 but you're certainly not getting the rated efficiency gain of CFLs. By contrast, if you're cooling your home (i.e., via AC), then not only is the heat waste but you then consume more energy by running the AC more to cool the house.

1 The physics here is a just a little complicated, but again the basic ideas not so much. When you burn fossil fuels locally to produce heat, you can arrange to capture the energy of the reaction quite efficiently (with the losses being in emitting exhaust that's hotter than the ambient temperature). So, if you're burning oil or gas to heat your house, this is quite efficient. By contrast, if you're using resistive electric heat, the fossil fuels are burned remotely and then turned into electricity and run to your house where you run them through wires to produce heat—just like a lightbulb but here the light is the waste and the heat is the intended output. Luckily, for second law reasons it's pretty easy to tune for a very high heat/light ratio. So, because of generation inefficiencies and transmissive loss, electric resistive heat is less efficient than locally burned fossil fuels. But there's not much efficiency difference between electric resistive heat and lightbulbs as long as you're lighting your house anyway. By the way, that while it's easy to burn fossil fuels for heat efficiently locally, it's not so easy to burn them for power locally, which is why plugin hybrids and electric cars are more efficient than regular internal combustion engines or even regular hybrids.

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In specific, if you are heating your house with something more efficient than electric heat, you are better off using that than the byproduct of the incandescent bulb. Gas heating is almost always more efficient than electric heat due to transmission losses in the electricity grid, so it is almost always better to not generate heat using incandescent bulbs, but to use CFLs instead.

I heard an interesting argument against CFL's efficiency recently. People who switch over to CFLs don't like the new color of the paint in their house and tend to repaint sooner than if they had stayed with the incandescent bulbs, and doing a repaint uses a lot of energy, and ...

The places within your house are not necessarily the same places as the places that you want heat, even if overall you want your house warmer rather than cooler. Your CFL or incandescent lamps are generally all up near the ceiling (or in the ceiling if you have cans). The place you want heat is generally beneath the floor. You might also want light in the kitchen, but heat in the bedroom. You might be able to design some kind of heat pipe to direct the bulbs' heat around the house, but I suspect it wouldn't work super well.

So anyway, in our remodelled house, we have sub-floor hydronic heat (heated by a tankless gas fired boiler), and LED lights throughout. The biggest innefficiency is probably the overkill on the 120 AC -> 12 DC transformers for the low-voltage lighting, which are designed for loads of ~500 watts per ~10 bulbs, where with LEDs we'll be running at more like 30 watts per ~10 bulbs.

Forgot to point out: you need about a transformer per ~10 bulbs so you don't drop too much current on the lines to each bulb.

When thinking about heating, you also have to consider heat pumps -- which, under certain circumstances (which happen to be present most of the time for most locations in the US), can introduce more heat into the house than even a 100% efficient conversion of electricity to heat would provide. So, even in areas where natural gas isn't readily available, you're still better off producing light with as little heat as possible, and turning to other mechanisms -- such as heat pumps -- for comfort heating.

The point about paint is one I'd never considered, but it makes sense. I've managed to get some really disgusting looking colors off cheap fluorescent bulbs before (our orange cat is a good litmus test -- he turns puke brown in cheap lighting). Verilux has recently introduced a line of full-spectrum CFLs (93 CRI, IIRC) that should address this issue to some degree (I have their tube fluorescents in the kitchen with good effect) -- although, for the best color balance, I still haven't found anything that rivals incandescent. That's why I still have halogen bulbs in the dining room -- CFLs and food can have bad visual interactions.

Yeah, yet to be seen how the "warm white" LED spectrum makes things look funky. I did some basic testing with a single "warm white" LED bulb and things looked better than I'd expected -- but I wasn't exactly extensive in my testing. I can picture some foods, as you say Adam, might be a little scary.

Yeah, I know some people are really bugged by the CFL colors, as some people are bugged by normal fluorescent lights. Presumably, this isn't a big problem unless some idiot manages to get incandescent lights banned. If it bugs you, then pay a little extra on power to get more pleasing light.

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