This article in Lunar Accents, though somewhat technical, gives some useful information that helps me understand LED (light emitting diodie) technology a bit better. It explains, in part, why LEDs can appear so much more intense than regular bulbs, and how to understand the various units of measurement.
I’ll summarize the information here.
- Beam angle: Ranging between 0 and 360 degrees, it is the direction light is emitted by a particular bulb. The common incandescent bulb generally has a beam angle close to 350 degrees because it sends light in all directions except where it plugs into the light socket. LEDs on the other hand can be focused or dispersed. A laser pointer likely has a beam angle close to 1 degree but some bulbs can have a much wider beam angle.
- Luminous flux: A measure of the energy radiated from a bulb measured in time over wavelengths visible to the human eye. The unit of measurement used for luminous flux is lumens or lm. The number of lumens produced by an LED bulb are constant regardless of the beam angle, even though the light may appear more intense as the beam angle decreases.
- Candela: This is the luminous intensity of light in a particular direction. In other words, how intense the light appears as a result of a combination of luminous flux and beam angle.
- Negative relationship between beam angle and candela: As the beam angle increases, the intensity of the light decreases because the light is dispersed over a wider range. On the other hand, as the beam angle decreases, the light becomes more focused, which results in a more tightly-focused, intense beam of light.
One of the things I take away from this article is the knowledge that the apparent brightness of an LED is the result of two factors (beam angle and luminous flux). Paying attention to these two will certainly make finding LEDs that are a good fit less challenging.