Glossary of Lighting Terms


A beam angle is a measurement of how the light is distributed. PAR lamps have a fairly narrow beam of around 40-degrees – an A19 or Globe lamp would have a beam angle of 360-degrees as the light shines all the way around but is less intense.

By selecting a light with a wider beam angle, you don’t get any extra light; it is just spread out further. The brightness (measured in lumens) remains the same, but the beam intensity (measured in candelas) increases. The downside to a wider beam angle is that it’s not as intense and the center of the beam of light wouldn’t go as far. Choosing the right beam angle can make a big difference in a room, but you don’t always have the option so if you know which beam angle you want from start this can often limit your options to just a few LED downlights.

A narrow beam angle of 25-degrees is known as a “spot.” Wider beam angles of 60-degrees are known as “flood beams,” and even wider beams are known as “wide flood beams.”


This refers to the part of the light bulb that secures into the socket. The most common type is the Edison Screw.


This can be used to describe either the finish of the glass on the bulb or it can describe the color appearance from a bulb. For instance, you often see warm white lighting in restaurants or hotels, while cool, crisp white lighting with a blue tinge is often used in offices or hospitals.


Light bulbs don’t all fail at exactly the same time. Typically, you classify the life of a lamp based on an average figure of 50% failure. So, if you have 100 light bulbs that have been rated at 1,000 hours of life, you can expect that after 1,000 hours of use, you will still have 50 lamps working.


Lumens are the amount of light the lamp puts out.


The base unit of luminous intensity in the International System of Units (SI); that is, luminous power per unit solid angle emitted by a point light source in a particular direction.


Refers to the amount of perceived light on a surface. There are numerous agencies that require specific foot candles in specific areas. While each building agency and municipality has their own codes that govern this, the following table illustrates a good rule of thumb.


Kelvin is a unit of measurement that determines absolute thermodynamic temperature.


The SI derived unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is equal to one lumen per square meter. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface.


Refers to the amount of energy a lamp uses. For compact and linear fluorescent, the ballast is only rated for a certain amount of wattage. Installing a lamp with a higher wattage than its rating will cause it to fail. For incandescent and halogen lamps, a wattage higher than the textures rating will result in too much heat.