Saving Energy by Turning Off Lights | Direct Energy Blog

Saving Energy by Turning Off Lights

One of the simplest measures you can take to save energy around your home is turning the lights off when you aren’t using them. If you are wondering why you should turn off the lights when you aren’t occupying a room, take heed of a number of benefits you can gain from the simple act of flicking a switch:

  • Reduce electricity usage
  • Extend the life of your light bulbs
  • Save money on electricity bills
  • Buy light bulbs less often

Turning off the Lights: The 15 Minute Rule

A general rule of thumb for an energy-efficient home has long been that if you are going to be out of room for 15 minutes or more, turn the lights off. If you’re coming back in less than 15 minutes, you can leave them on. Given today’s wide range of lighting options that provide varying levels of built-in efficiency, you might wonder if that rule still holds true. Read on to learn more about why we should turn off the lights and how using different bulbs can affect your energy-saving strategies.

Saving Energy by Turning Off Lights | Direct Energy Blog

Fluorescent Lights

Many people believe that fluorescent lights require more energy to turn on than they use to glow and therefore it is cheaper to leave them on rather than turning them off. This misconception came about because fluorescent lights traditionally took a long time to warm up due to the way the technology functioned, with bulbs 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 so when it gets very cold, the bulbs might barely glow at all.

However, modern bulbs like Compact Fluorescent Lights or CFLs are designed to function more efficiently at room temperature. Many use rapid start ballasts that use 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 do have a minute or two 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 the start, while yellower (tungsten-balanced) CFLs seem more orange.

Does the 15 Minute Rule Apply?

While you won’t save any energy by leaving fluorescent lights on when you aren’t using them, you can rapidly shorten their lifespan by degrading the light’s electrodes if you turn them on and off over a short period of time. Therefore, to extend a fluorescent bulb’s lifetime, it’s better to leave it on for longer than five minutes at a time. A rule of thumb from recommends the following:

  • If you will be out of a room for 15 minutes or less, go ahead and leave the lights on.
  • If you’re leaving for more than 15 minutes, turn the lights off.

Saving Energy by Turning Off Lights | Direct Energy Blog

Incandescent Bulbs

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 at the flick of a switch. Their main problem, though, is that light is a byproduct of their filament wire heating up, so their main energy output is 90 percent heat. Not only do they consume a substantial amount of electricity, they have shorter lifespans than other types of bulbs.

The lifespan of incandescent lights is not affected by rapid switching, so there is no compelling reason not to switch off the lights when not in use. Leaving incandescents on for too long can harm your efficiency in another way, too, since their heat output adds to your home’s cooling load during the summer.


LED bulbs use semi-conductors, are low wattage, put out nominal amounts of heat and resist vibration. Since LEDs produce light through electro-luminescence, frequently switching on and off has no effect on them. Even though they only use a fraction of the energy of an incandescent bulb, you’re still saving energy by turning off the lights, so there’s no reason to leave them on when you leave the room. The simple rule for using these in an energy-efficient home is to turn them off when you don’t need them.