EagleLight’s LED University: Light Bulb Brightness Explained
Various Definitions of LED Brightness: lux, lumen and watt
In this lesson we are going to define some of the many terms used in LED light bulb brightness such as watt, lumen, and lux.
In this LED university course we will discuss:
- measuring the amount of light produced from an LED light source
- measuring the amount of light we see from an LED light source
- measuring the amount of usable light produced from an LED light source
This discussion is not a rigorous scientific analysis. However, it is intended to offer an understanding of a few of the various terms used related to LED light bulb brightness.
Watt as a measure of LED light bulb brightness
A measure of brightness used in the past was the wattage of a light. With more efficient lighting products like CFL and LEDs, use of the watt is no longer an accurate means of determining brightness across multiple lamp technologies. For example: a 75 Watt incandescent bulb, 18 watt CFL and a 9 watt LED may all produce the same amount of usable light. Obviously watt is not longer a viable means to measure the brightness of a light source across differing technologies.
LED Lumen as a measure of brightness
The LED lumen measures the total amount of visible light from a light source. Unfortunately some light may be used to light areas not even visible to the viewer. Such as the lighting of the inside of a fixture. This is why the measure of the light found on the projected surface is often a much better measure of applicable light. LED lumens often times are less than the lumen measure of another light technology for the same brightness on a working surface. This is due to the directed nature of LED packaging. This direction of the LED lumen results in greater use of the available light.
LED Lux as a measure of light bulb brightness
The measure of the amount of visible light on a surface, like the lux, is a good way to determine the amount of “usable” light created by a light source.
|Light Measurement||Definition||Form of Measure|
|Radiant Flux||the total power of light: visible and non-visible light||watt (W)|
|Luminous Flux or Luminous Power||the perceived power of light adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light||lumen (lm)|
|Luminous Intensity||the amount of lumen on a square meter||lux (lx)|
|Luminous Efficiency||the amount of visible light produced per each watt consumed||lumen/watt (lm/W)|
What to compare when buying LED lightbulbs
For the Scientist:
For more technical information, physics and some math on the topics in this lesson you can refer to the Wikipedia definitions.