Incandescent lamps, commonly known as light bulbs, have a lifespan that will typically be much less than the number of hours listed on the package. There are many reasons for this.
To begin with, the rated number of hours is generally achieved in the laboratory under ideal conditions. This includes constant voltage and electrical frequency, constant temperature, no vibration, and no on/off cycling. It’s really the filament (which is the fine, wire-like material in the bulb) that determines the life of the bulb, so anything that affects the filament will affect the life of the bulb.
Several factors affect the typical life of an incandescent light bulb.
- shock and vibration
- operating voltage
- inrush current
- Temperature
- cycle on/off
Let’s start with shock and vibration. The delicate bulb filament will weaken when subjected to shock and vibration during shipping and handling, when handled by the consumer, and when in a device subject to shock and/or vibration. Even closing doors, as well as strong winds and storms cause vibrations through the walls and ceilings of houses, and this affects the filament.
The operating voltage affects the bulb filament in the sense that if the bulb voltage fluctuates and is generally lower than the rated amount the bulb will last longer, but if the voltage is generally higher then the filament will have a shorter shelf life. Voltage spikes also have a detrimental effect on the bulb’s filament, shortening its lifespan.
Inrush current occurs when a light bulb is turned on and is quite destructive to the filament. When the bulb is turned on, the input current can be up to ten times higher than the typical operating electrical current. It is the thermal shock caused by the inrush current surge that does the damage.
The operating temperature affects the filament in the sense that a higher temperature reduces the life of the bulb. Using a bulb with a wattage greater than the fixture’s rating will cause increased temperatures and therefore shorten the life of the bulb. Ventilation around a light bulb will increase its lifespan. Many fixtures have very little ventilation and get very hot inside, even with lower wattage bulbs. Your bulbs will last longer in enclosed fixtures if you can use the smallest possible wattage that still provides an adequate amount of light.
The on/off cycle subjects the filament to the destructive effects of the inrush current described above each and every time the bulb is turned on. Therefore, the life of the bulb can be increased by minimizing the number of times the bulb is turned on and off. If you plan to return to a room in a few minutes, it may be better in the long run to leave the light on rather than turn it off and then back on again.