Amperes (amps)

The electrical current flowing through a bulb. See Volts, amps and watts: What’s the difference? below.

Average rated life (lamp life)

The number of hours a bulb will last when it is burned at its rated voltage under controlled laboratory conditions.


The part of the bulb that provides electrical contact to the bulb and typically supports the bulb.

  • Cylindrical bases are usually measured by millimeters in diameter.

  • Two-pin bulbs are usually measured by millimeters center-to-center on the pin.

Color temperature

The color of light, i.e., how warm (yellow-white) or cool (blue) a bulb is. Color temperature is measured in Kelvin (see definition below).

Bulbs with higher color temperatures will appear cooler than those with lower temperatures.

Color rendering index (CRI)

How a light source will illuminate objects and surfaces.

  • A high CRI makes virtually all colors look natural and vibrant.

  • A low CRI causes some colors to appear washed out or take on a different hue.

A CRI in the 80s will give you a true color portrayal.

Light center length (LCL)

The distance between the center of the bulb filament (or light field) and the bottom of the base.

Lumens (LM)

The quantity of light given off by a bulb, regardless of direction. Also known as luminous flux.

Kelvin (K)

A measure of color temperature (see definition above). Natural daylight is measured at 6000K.

  • Warmer (yellow-white) temperatures fall in the 2700-3000K range.

  • Cooler (blue) temperatures fall in the 4100K range.

Maximum overall length (MOL)

The length of a bulb, from the top of bulb to the bottom of the base, typically expressed in inches.

Operating position

The recommended bulb position to get the best performance:

  • U: Universal

  • Hor: Horizontal

  • BD: Base down

  • BU: Base up

  • BDTH: Base down to horizontal


A code that defines the bulb shape and maximum diameter size, measured in eights of an inch.


The force of electricity going through a wire. See Volts, amps and watts: What’s the difference? below.


The amount of electricity (power) a bulb will use. See Volts, amps and watts: What’s the difference? below.

Volts, Amps and watts:  What's the difference?

To understand how these three terms relate, think of a water hose.

  • Current, measured in amps, is the amount of water flowing through a hose.

  • Voltage is the pressure with which water is pushed through a hose.

  • Wattage represents power, which is the product of both the current (amps) and the voltage of a device.

In simplest terms, adjusting the amount of water (amps) or the force of the water (voltage) will determine the power rating (watts).