How to Measure Light Bulbs

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As any frustrated physicist will tell you, light is complicated. And getting it to do what we want is even harder. So designing lighting for residential and commercial purposes CAN be a confounding process. However, with a few tools and a little bit of know-how we can chop it down and make the whole thing a little more approachable. The first step is to know how much light is coming out of a bulb and how that hits the surrounding area - but to do that, we need to cover some basics about how light works.

Some quick vocabulary

First things first - when we’re talking about lighting equipment, there exists a different vocabulary from what most people are used to. So before we continue, we should get a few of the confusing terms straight.

Most notably is the word lamp. In lighting, a lamp is a piece of equipment that, when connected to an electrical power supply, produces visible light. Often called a bulb, these are the most delicate parts of a light.

What most people would call a lamp is actually referred to as a fixture in lighting terminology. The fixture is the body that holds a bulb - it contains the physical pieces that direct and shutter the light.

A filter is a generic term for something that reduces the intensity of a light mute button. A filter can selectively reduce power by wavelength, producing different colors, or generally, to diffuse the light, making it less offensive to the human eye.

How is light measured?

Light is measured in two ways: in terms of illuminance and irradiance. Both measure the intensity of light, but there is one key difference. Irradiance is a straight measure of the power transfered from the source to the observer - this is measured in watts per square meter. Irradiance is usually used for safety purposes, not for commercial lighting. For measuring bulbs, Illuminance is usually used.

Illuminance is the measure of light energy transfered from a source, but it is altered, according to the luminosity function, to account for the differences in the ways the human eye perceives different wavelengths of light. The common measurements lumen and lux are both measurements of illuminance.