Kelvin is a unit of measurement used to describe the hue of a specific light source. This is not necessarily related to the heat output of the light source but rather the color of the light output. The higher the Kelvin value of the light source, the closer the light's color output will be to actual sunlight.
Higher color temperatures (5,000 K or more) are called cool colors (blueish white); lower color temperatures (2,700–3,000 K) are called warm colors (yellowish white through red).
A lumen is a unit of standard measurement used to describe how much light is contained in a certain area. Lux: 1 lx = 1 lm/m2.
Fittings (Caps and Bases)
The part of the lamp that connects into the light fitting is generally known either as the “cap” or “base”. This provides the electrical contact and also often the physical location of the lamp. A vast variety of caps and bases exist in order to help make sure that only the correct type of lamp is used in any given fitting.
Named after the pioneering inventor Thomas Edison, the Edison Screw or “ES” lamp fitting is used worldwide in a vast range of applications.
The most popular ES or E27 fitting is 27mm diameter and is widely used in both the US and Europe. The SES or E14 is often used for smaller decorative fittings, chandeliers, and appliance bulbs - predominantly in the UK and Europe.
The most common halogen spots are low voltage (MR16) or twist and lock (GU10) mains versions.
Bayonet Cap with its “push and twist” action (also known as BC or B22) is used on regular light bulbs. It is 22mm diameter and with two locating lugs.