There are a lot of important factors to look at when choosing the right light fixtures . Lumens per watt, fixture type, warranties, color temperatures are all super important, but how about light distribution?
Outdoor light fixtures use light distribution patterns. The patterns define how light is dispersed from a fixture and is defined by the point at which 50% of the fixture’s luminous intensity is met. You will see these distributions used regularly in area lighting, flood lighting & roadway lighting. The industry has identified 5 main types of light distribution patterns. There are others which get into asymmetrical or symmetrical types but we will not discuss those today.
The Type I distribution is great for lighting walkways, paths, and sidewalks. This type of lighting is meant to be placed near the center of the pathway. This provides adequate lighting for smaller pathways. Type I is a two-way lateral distribution having a preferred lateral width of 15 degrees in the cone of maximum candlepower. The two principal light concentrations are in opposite directions along a roadway. This type is generally applicable to a luminaire location near the center of a roadway where the mounting height is approximately equal to the roadway width.
The Type II distribution is used for wide walkways, on ramps and entrance roadways, as well as other long, narrow lighting. This type is meant for lighting larger areas and usually is located near the roadside. You’ll find this type of lighting mostly on smaller side streets or jogging paths.
Type II light distributions have a preferred lateral width of 25 degrees. They are generally applicable to luminaires located at or near the side of relatively narrow roadways, where the width of the roadway does not exceed 1.75 times the designed mounting height.
The Type III distribution is meant for roadway lighting, general parking areas and other areas where a larger area of lighting is required. Type III lighting needs to be placed to the side of the area, allowing the light to project outward and fill the area. This produces a filling light flow.
Type III light distributions have a preferred lateral width of 40 degrees. This distribution is intended for luminaires mounted at or near the side of medium width roadways or areas, where the width of the roadway or area does not exceed 2.75 times the mounting height.
The Type IV distribution produces a semicircular light meant for mounting on the sides of buildings and walls. It’s best for illuminating the perimeter of parking areas and businesses. The intensity of the Type IV lighting has the same intensity at angles from 90 degrees to 270 degrees.
Type IV light distributions have a preferred lateral width of 60 degrees. This distribution is intended for side-of-road mounting and is generally used on wide roadways where
the roadway width does not exceed 3.7 times the mounting height.
The Type V distribution produces a circular distribution that has the same intensity at all angles. This distribution has a circular symmetry of candlepower that is essentially the same at all lateral angles. It is intended for luminaire mounting at or near the center of roadways, center islands of the parkway, and intersections. It is also meant for large, commercial parking lot lighting as well as areas where sufficient, evenly distributed light is necessary.