The cost-effectiveness of turning off lights depends on the type of bulb and the cost of electricity. For several reasons, the type of lightbulb that you use. All light bulbs have a nominal or rated operating life, which is affected by how many times they are switched on and off. The more often they are switched on and off, the lower their working life.
Incandescent lights should be switched off whenever they are not needed, because they are the least efficient type of lighting. 90% of the energy they use is emitted as heat, and only about 10% is emitted as light. Turn off the lights will also keep the room cooler, an extra benefit in the summer.
While halogens are more efficient than conventional incandescent bulbs, they use the same technology and are far less efficient than CFLs and LEDs. It is therefore best to turn off these lights whenever they are not needed.
Since they are already very efficient, the cost-effectiveness of turning off CFLs to save energy is a little more complicated. The general rule of thumb is this:
- When you're out of the room for 15 minutes or less, leave it on.
- When you're out of the room for more than 15 minutes, turn it off.
The working life of the CFLs is more influenced by the amount of times it is turned on and off. Generally, you can prolong the life of a CFL bulb further by flipping it on and off less often than if you actually use it less.
It's a common misconception that CFLs use a lot of energy to get started, and it's best not to turn them off for a short time. The amount of energy varies between manufacturers and models—however, ENERGY STAR© rated bulbs are needed to withstand rapid cycling for five-minute intervals to ensure that they are able to withstand regular switching.
In either case, the comparatively higher "inrush" current required will last for half a cycle or 1/120th of a second. The amount of energy used to supply the inrush current is equal to or less than a few seconds of regular light activity. Switch off the fluorescent lights for longer than 5 seconds will conserve more energy than will be used by turning them back on again. The main problem, therefore, is the expense of the energy saved by switching off the light compared to the cost of changing the light bulb. This, in essence, determines the shortest cost-effective timeline for turning off the fluorescent light.
The value of energy saved by turning off the CFL depends on a variety of factors:
- The price and charge of energy to its consumers depends on the customer's class, which is usually residential, commercial and industrial. Within - class, there may be different rate schedules.
- Some utilities can charge different rates of electricity consumption at different times of the day. It is usually more costly for utilities to produce electricity during such times of high demand or usage, called peaks.
- Some utilities can charge commercial and industrial customers more per kilowatt-hour (kWh) during peak periods than for off-peak usage.
- Certain utilities can also charge a base rate for a certain level of usage and higher rates for growing consumption blocks.
- Sometimes the utility adds miscellaneous service charges, basic charges, and/or taxes per billing period that may be averaged per kWh consumed if they are not already included in the rate.
The working life of the light emitting diode (LED) is not changed by switching it on or off. Although the life of fluorescent lamps is shortened the more often they are turned on and off, there is no detrimental impact on the life of the LED. This function gives LEDs a range of distinct advantages when it comes to service. For example, LEDs have an advantage when used in conjunction with occupancy sensors or daylight sensors that rely on off-the-shelf operation. Also, unlike conventional systems, LEDs are turned on at maximum brightness almost immediately, without delay. LEDs are also largely unaffected by vibration since they do not have filaments or glass enclosures.