A lesser known benefit of LED lighting is the ability to direct light uniformly, where it is needed most, without overspill. A knowledge of light distribution patterns can help a lighting specifier choose the best luminaires for a given application; reducing the number of luminaires required, and consequently, the electrical load, power distribution costs, and labor costs
Light distribution patterns reference the spatial distribution of the light as it exits the luminaire. Every luminaire will have a different pattern depending on the globe design, material selection, placement of the LEDs, and many more defining characteristics. However, to make things easier, the industry groups the luminaire’s pattern into several already classified and accepted patterns. The IESNA (Illuminating Engineering Society of North America) classifies roadway, low and high bay, task, and area lights into five major patterns. NEMA (National Electrical Manufacturer Association) categorizes floodlights based on their horizontal and vertical spreads.
IESNA uses five main types of light distribution patterns ranging from Type I to Type V. In the hazardous and heavy industrial world, you will typically see Type I, Type III, and Type V.
A common practice in the industry is the further break down the five main groups into additional light spreads. You can take the Type 5 symmetrical circular pattern and depending on the spread can be further classified into a narrow, medium, or wide configuration. This can be very useful depending on your mounting height and exactly where you want most of the light. If you have very high mounting height you could use the Type 5 Narrow beam to push the light down without it spreading too much; keeping the main beam closer together. Whereas you might use the Type 5 Wide pattern for a very low mounting height where you need the light to spread as quickly as possible; giving you additional light on the outer edges.
NEMA classifies floodlight patterns based on their horizontal and vertical spreads as seen on the table below. Each NEMA pattern will have a numerical value for the horizontal spread by a numerical value for the vertical spread.
FIELD ANGLE RANGE
10° to 18°
240 ft (73 m) and Greater
18° to 29°
200 to 240 ft (61 to 73 m)
29° to 46°
175 to 200 ft (53 to 61 m)
46° to 70°
145 to 175 ft (44 to 53 m)
70° to 100°
105 to 145 ft (32 to 44 m)
100° to 130°
80 to 105 ft (24 to 32 m)
130° and Up
Under 80 ft (24 m)
Using the picture below you can see how the NEMA 7X7 pattern is very close to the NEMA 7X6 pattern, except that the NEMA 7X6 pattern doesn’t quite have the same vertical spread or light throw causing the light to drop off faster. While NEMA 5x5 is a narrower beam allowing you to reach out further distances.
Overall, these different light distribution patterns are designed to help you get the optimal amount of light exactly where you need it the most. By specifying the correct pattern, you can reduce the size of the luminaire, reduce the number of luminaires needed, and ensure you are meeting all your lighting requirements. If you would like more information please visit us at www.masteringled.com
Ellen Helm | Manager, Appleton Lighting |Electrical & Lighting
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