Apr 2013

Directional Light Sources

Always start with the light bulb when deciding how you want to light a room or a wall or a piece of art or anything. The fixture is secondary to the lamp (how lights bulbs are referred to by lighting professionals). We are discussing directional lamps here so one of the most common lamp types is the MR16, a 2 inch diameter mirrored reflector. It is used extensively in recessed lights, track fixtures, monopoints and landscape lights. It is one of many directional lamps available today. Other directional lamps include PAR, BAR and AR. These designations are followed by numbers, 16, 20, 30, 38, etc. The numbers are the measurement of the face of the light bulb in 1/8th’s of inches. So a PAR38 is 4.75″ in diameter.

To determine which directional light source to use you need a basic understanding of photometrics, the measurement of the properties of light. Most fixture and light bulb manufacturers publish photometric tables that show how different lamps perform. These tables show footcandle levels at different distances from the light source and different aiming angles. They also show the distribution of light at different distances from the center beam of the light bulb. The center of the beam of a directional light is the brightest spot and the number of footcandles at that point is determined by Center Beam Candle Power, CBCP. Therefore you will see this terminology used when describing directional lamps. There is a lot or great information available in the UL app “LightSmart” that you can download for free at the app store.

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