21W 12V B15S

Wattage

How much power the bulb draws. Between bulbs that use similar technology, higher power usually means brighter light.

Voltage

It is important to match the voltage with your existing bulbs/fittings, otherwise it is likely to blow immediately. The voltage is usually printed on the bulb.

Code

Manufacturer specific codes which may be printed on the lamp or packaging.

Life Hours

Average life expectancy of bulb. Sometimes external factors can impact the life of bulbs, for example using non-dimmable compact fluorescents with a dimmer, or standard incandescents in environments with a lot of vibration, (use Rough Service bulbs) or faulty starters on fluorescent tubes.

Base

The base should match the fitting.

Dimensions

Physical size of the bulb. Sometimes given as an industry code.

Colour

Colour of the light emitted from the bulb. White bulbs are usually described by their colour temperature, with higher temperatures giving brighter, whiter light.

Finish

The finish applied to the glass of the bulb. Different finishes give the lamp a different appearance. In an open fitting "frosted" opaque finishes are often used to diffuse the bright filament.