Matthew's Journal

If you’re serious about energy efficiency, use energy saving lightbulbs. They don’t work with dimmer switches; I interpret this to mean that you have to leave the dimmer switch at full on and click it on and off, rather than meaning that you can’t use an energy saving lightbulb in a socket controlled by a dimmer switch, but I don’t know for sure.

I believe energy saving lightbulbs generally have a longer life than normal lightbulbs also, but I don’t know where I got that from.

I don't know, but I used to have a dimmer switch in my childhood bedroom and loved playing with it. Eek, bright lights!

The only dimmer switch that I'm familiar with requires to be turned down all the way before it switches off (it's a knob going from 0 to "dimmest" with a click when turned anticlockwise, and then gets brighter as you turn it further in that direction).

I would think that the dimmer switch would last better if just clicked.

Also, if just clicked, the lightbulb would be on for slightly less time (you'd switch it off almost instantly rather than taking 2 seconds to do so), and would therefore use less energy. That's the only apparent difference in energy use that I can see.

I assume it's a modern dimmer that uses a TRIAC circuit to switch the light on and off rapidly. I think they contain capacitors to smooth out the choppiness of the current too.

1. So up to the point that you come to turn the light off, energy use is the same for both cases. If you then turn the switch off, energy use stops, whereas when you turn the dial down a small amount of energy is used until you turn off the light. Therefore dimming and turning off uses fractionally more energy. However, when you come to turn it on again you save the same amount of energy in the dimmed down state (provided you dim up and down at the same rate). But the circuit will use a very small amount of energy to drive the transistors in the dimmer. So the answer is turning it off immediately saves a tiny fraction of energy, namely the energy consumed by the during the period of dimming down and up. Dimming the switch to minimum before turning it on and off uses a minimal amount of extra energy.

2. Light bulbs burn out when the tungsten in a section of the filament evaporates away so much that there's a break. Switching on from cold means more current is drawn because cold filaments have more resistance, but the warming up happens very quickly. This surge can cause the bulb to blow (it's why bulbs often blow when you turn the light on). You would think that turning up the dimmer slowly is like a soft-start device such as a thermister, which will extend the life of the bulb, but we're chopping the current, rather than reducing the current draw, so a dimmer is a very poor soft-start device. And good slow-start thermistors only minimally extend the life of bulbs anyway. So dimming the switch to minimum before turning it on and off will result in a minimal life extention for the bulb.

That's what I think, anyway.

Assuming the light bulbs are conventional incandescent tungsten-filament affairs, it makes no difference how gradually you turn them off, but it certainly prolongs bulb life to dim them up rather than turn them on abruptly.

If you need convincing, think about lights that don't have dimmer switches, and note that they burn out when being switched on much more often than they burn out in use.

Personally, I favour the kind of dimmer that one rotates fully anticlockwise to turn off, for precisely this reason.

As for energy saving, I doubt it makes much difference, except of course that light bulbs themselves cost energy to make, and you'll save some of that if you make them last longer. Arguably you save a little energy if you turn the light on gradually, simply because it's on fully for marginally less time. But then you counteract the saving if you turn it off gradually. (-8

What is inefficient, though, is leaving the lights dimmed. Incandescent bulbs aren't terribly efficient at the best of times, of course, but when dimmed an even greater proportion of the energy they consume is emitted as heat. If you find yourselves always keeping the lights dimmed, change to lower-wattage bulbs.

For the first one, full on or full off will be fairly similar, although I guess full off may actually be marginally better. What may be worst is half-way because of the way most cheap dimmer switches work.

For the second one, turning off immediately uses less energy than adjusting to minimum and then turning off because you turn off sooner. Once off, you can adjust to minimum for the next time it's turned on.

For the third, you missed the option that states I know a lot about electrical stuff, and know my answers may not be correct.

D

Stop wasting time and leave the thing on full. Dim it only when you want it dimmed. Or use candles, they're much nicer.