Turn Off the Lights to Save Money and Extend the Life of Your Light Bulbs
Surely, I can’t be the only parent who experiences such delightful conversations with his kids:
(Me) “Turn the lights off in your room if you’re not going to be in there.”
(Teen) “Like, I only left for a second! I’m getting a snack!”
(Me) “So you’re playing video games, now?”
(Teen) “I’ve only been here for like, 15 minutes! Like besides, it’s cheaper to leave a fluorescent light on than to turn off. I mean, like, you’re always criticizing…”
Let’s just freeze this tender scene right there. To have a more energy efficient home, there are three good reasons for turning off lights when you aren’t using them:
- To reduce electricity usage
- To extend the life of light bulb
- Over the long haul, by being energy efficient, your family can save money quite easily.
A good rule of thumb for an energy efficient home has been that if you are going to be out of room for 15 minutes or more, then turn the lights off. Shorter than 15 minutes, you can leave them on. The trick is that this rule varies depending on the type of lighting that you’ve got. So, let’s look at the types of lights we have in our homes and see how this rule works in the real world.
First of all, there’s fluorescent lights. Fluorescent lights have a long history of taking time to warm up. this is because fluorescent lights are filled with inert gas at low pressure and a little bit of mercury. When switched on, the tube’s electrodes shoot electrical arcs across the tube to each other. This vaporizes and excites the mercury to release ultra violet photons (light). The UV photons excite the phosphor coating inside the tube and it gives off light. Older fluorescent tubes need to pre-heat the electrodes in order to vaporize the mercury (at about 40°C or 104°F) for the phosphor coating to begin glowing. At low temperatures, the mercury in the tube is actually dispersed liquid droplets. A pal of mine has a pole barn in Iowa lit by big, old T12 fluorescent tubes. When the air temperature is 20°F or colder, the tubes glow very dimly and look like they’re filled with swirling pink water. At below 0° F, they barely glow at all.
As a consequence, many people believe that fluorescent lights (including Compact Fluorescent Lights or “CFLs”) require more energy to turn on than what they actually use and that it is cheaper to leave them on rather than turning them off.
Balderdash and piffle!
Many fluorescent bulbs, including CFLs are designed to function more efficiently at room temperature. Many use a rapid start ballast that uses a small amount of current to keep the electrodes warm enough so that the light fires up in a fraction of a second. Some bulbs also use a fast heating process where a high pulse of electricity heats the electrodes. This pulse, however, lasts 1/120th of a second. So the actual start-up current draw compared to the bulb or tube’s output over a minute or longer is trivial. Some cheaper CFLs have a certain amount of lag time until they brighten up to the spectrum they have been calibrated to. That is, daylight CFLs may have more bluish tinge at start; yellower (tungsten-balanced) CFLs seem more orange. It usually take a minute or two until they hit their advertised output.
In an energy efficient home, The main challenge for using fluorescent bulbs is that turning them on and off every five minutes will rapidly shorten their lifespan by degrading the light’s electrodes. Therefore, to extend a fluorescent bulb’s life time, it’s better to leave it on longer than 5 minutes.
Incandescent bulbs (including halogens) rely on a wire filament held inside a vacuum. When turned on, the filament heats and emits light. Both regular incandescent bulbs and halogen lights are great at producing instantaneous light. When you want light (even if you’re in an Iowa pole barn when it’s -30°F), you have it at the flick of a switch. Their main problem, though, is that light is a by product of their filament wire heating up. Incandescent bulbs main energy output is 90% heat. And for this reason, they have shorter lifespans.
The best time to turn off incandescent lights is simply when you are not using them. Their lifespan is not effected by rapid switching (although, keeping the light fixture cool, vented and dry will help the bulb last longer). In an energy efficient home during the summer, rely on them less because their heat output adds to your home’s cooling load.
LED bulbs use semi-conductors. They are low wattage, put out nominal amounts of heat and resist vibration. Since LED’s produce light through electro-luminescence, frequently switching on/off has no effect on them. Even while they might use a fraction of the energy of an incandescent bulb, you don’t want to leave them on all the time. Again, the simple rule for using these in an energy efficient home is to turn them off when you don’t need them on.
A Timely Rule of Thumb
All of which brings us back to our original rule of thumb:
If you will be out of a room for 15 minutes or less, leave it on.
If you will be out of a room for more than 15 minutes, turn it off.
Why 15 minutes? First of all, it’s long enough to prevent frequent on/off switching that damages fluorescent lights. Second, in real life, there are plenty of distractions that waylay our attention when we step out of a room, no matter what our intentions might have been. You might plan on going down the hallway for five minutes but something comes up and you’re away for thirteen. The point here is that is that you hadn’t planned to be gone for very long. Again, the same distractions can happen when you plan to be gone for longer than 15 minutes. Say that you’re going out to the store for 20 minutes and while you’re there you run into an old friend. Next thing you know, you’ve been gone for 40 minutes. The point here in this example is that leaving the lights on at home (especially incandescent bulbs) can really pack the minutes on to your energy bill.