How Long Can a Light Stay on?
The light bulbs in your home emit countless photons. These photons are then reflected and absorbed by objects in your room, lighting up the space.
Operating lighting fixtures uses a small amount of electricity, measured in kWh, which is added to your household energy usage. So how long can a light stay on without wasting energy?
Light bulbs are used for many purposes, from lighting a room to signaling an electronic device is on. Billions of them are in use around the world. They are typically made of glass and contain a filament that glows when electric current passes through it.
Most electric bulbs are filled with a gas such as argon or nitrogen to reduce the amount of convective loss in the filament, but the earliest bulbs were not filled with anything at all. The tungsten in these bulbs would become very hot and burn up quickly in regular air.
The life time hours listed on a bulb’s packaging are usually tested under ideal conditions, so they may be longer or shorter in real-world situations. Some other factors that affect the performance of a bulb are electrical surges, extreme cold, and vibration.
Halogen bulbs are a popular upgrade from traditional incandescent lightbulbs. They last longer than traditional bulbs, and are more energy efficient as well. In fact, halogen bulbs can produce anywhere from 12 to 29 lumens per watt of power, while traditional incandescent lightbulbs only offer up to 18 lumens per watt of power.
Halogens are nonmetallic elements with an outer shell that contains seven valence electrons. Because they are more electronegative than oxygen, halogens can easily gain an electron from another substance to satisfy the octet rule. This results in the formation of compounds with that other substance, including metal halides, which have similar properties as their parent element.
In a halogen light bulb, a tungsten filament is placed inside a heat-resistant envelope filled with halogen gas. When an electrical charge is applied, the filament heats up to about 2,500 degrees Celsius and emits light. In most cases, halogen lamps are mixed with a noble gas such as krypton or xenon to reduce their chemical reactivity.
CFLs use less energy than traditional incandescent bulbs and last about 10 times longer. Replacing just one 60-watt bulb with a 13-watt CFL saves the average household $30 in energy costs over its lifetime.
CFL light output is proportional to the phosphor surface area, so it takes time for them to reach full brightness after being switched on. Bare spirals typically take a minute to achieve their rated lumen output, although some premium CFLs are much quicker. Decorative cover styles, including globes and reflector shapes, have slower warm-up times – up to three minutes.
Unlike incandescent bulbs, which emit visible light as they burn, CFLs produce invisible ultraviolet radiation that excites the phosphor coating inside the tube to make it glow. This can cause discomfort for some people, particularly those with lupus or other auto-immune diseases who are sensitive to UV. CFLs also emit some levels of HF (radiofrequency) electromagnetic fields. Health Canada has determined that the EMFs produced by CFLs are negligible at 20 centimeters from the source and in line with international scientific guidelines.
LEDs use a special conductive material (typically aluminum-gallium-arsenide) to create photons that the human eye sees as light. Different types of LEDs are designed with lenses or reflectors to either concentrate the light in a small spot or spread it out over a wide area.
While LEDs can be left on for days, they still need to be turned off when not needed. They generate very little heat which makes them less likely to create a fire hazard or burn someone when touched. Their cooler running temperature also limits the amount of internal damage that can occur if they are cycled often like other bulbs.
Like other types of lighting, LEDs do not burn out but they will gradually lose their brightness over time. This is due to thermal management; the faster an LED is able to dissipate its heat, the longer it will last. You can control an LED’s brightness by adjusting the current it draws.