Most of us have been told to turn off the lights when we leave the room since we were small, even if it was mostly for financial cost. However, the financial cost effectiveness of turning off the lights varies according to what type of bulb you use and the cost of electricity. We all know that different lightbulbs have different efficiencies and this will obviously impact the cost of leaving the lights on.
However, did you know that different bulbs have different operating lives? The operating life is in turn influenced by how many times the light is turned on and off; i.e. the more they are turned on and off, the shorter their lifespan.
Incandescent lights are the least effective and release approximately 10 % of their energy as light and the remaining 90% as heat. Turning the lights off is therefore extra beneficial in warm climates as it could save you some energy on the airconditioning.
Halogen lights are more efficient, but it is still best to turn these lights off when not needed as they are not as efficient as CFL or LED lights.
CFL lights are very efficient, making the financial cost calculation a bit more complicated, and should be turned off if you are leaving the room for a longer period of time (>15 minutes). As their lifespan shortens with turning on and off, you will have to buy new ones quicker, therefore spending not only more money, but also creating more waste. These lamps also tend to use a lot of energy to get started so even in this regard it is best to turn them off only if it is for longer periods of time.
The operating life of LED lighting is not affecting by on and off switching and they almost instantly reach full brightness. This is therefore the most advantageous lighting for both financial and environmental sustainability.
When in doubt, turn off the lights if you are leaving the room for more than 15 minutes. If you are a forgetful person like me, you have plenty of automated options. There are timers, motion sensors or light sensors available to enable the light to turn on or off under certain conditions.
Most importantly, switch to LED lights whenever possible.