Connecting a light bulb's electrical contacts to the positive and negative terminals of a battery causes it to turn on and to draw power from the battery. The key to successful connection and operation is matching the bulb's operational range with the battery's voltage.
Contacts differ from bulb to bulb. Some are prongs extending from the bulb's base below the threading while others include a threaded contact and another, smaller one without threads extending from the base. Spring contacts, found in most flashlights, are a good connector.
Good combinations of bulbs and batteries according to capacity include:
- 3V flashlight bulbs and three D batteries in sequence.
- 12V interior car bulbs and eight battery cells in sequence.
- Regular 120V household bulbs require matching batteries which can be hard to find.
Batteries improperly matched to light bulbs will not light the bulbs effectively. If their voltage is too low, the bulb will produce no light. If it is too high, the bulb's filament could be vaporized and the bulb will be rendered useless. A close match might work, but it is unlikely to be as effective as a perfect match between voltage and capacity. Bulbs function inside a target temperature range rather than on a spectrum of effective light production.