Nema Beam Spread: Understanding Lighting Distribution

What is Nema?

NEMA is the National Electrical Manufacturers Association which is a trade association of electrical manufacturers founded in 1926. It is an ANSI-accredited organization that develops standards for electrical equipment used in North America, some of which relate to lighting systems.

What is Light Distribution?

Light distribution can be broadly characterized as narrow, wide, or somewhere in between. Spotlights have a narrow beam, usually less than or equal to 25°. The light is more focused and reaches farther than a wide beam. By contrast, flood lights have a wide beam, usually 45°-120°. The light illuminates a larger area but does not reach as far.

Many things affect beam spread and light distribution. Outdoors, the height of fixtures mounted on light poles can change the light distribution dramatically. The higher the pole, the better the distribution.

Nema Pattern Type

Another way that NEMA classifies light distribution is by pattern type. Each of the six types that NEMA identifies are used for different applications. They are illustrated here:

NEMA beam spread classifications are indicated by a number between 1 and 7 and are broken down in the chart below.

Nema Beam Spread Classifications

As you can see, the wider the beam gets, the shorter the beam projection distance is.

Type I

Pattern type: two-way 15° lateral distribution
Applications: sidewalks, paths, walkways
Fixture Placement: center
Ideal mounting height: equal to walkway width

Type II

Pattern type: 25° lateral distribution
Applications: narrow roadways, wide walkways, ramps and entrance roadways
Fixture Placement: at or near the side
Ideal mounting height: The width of the road should not surpass 1.75 times the mounting height

Type III

Pattern type: 40° lateral distribution
Applications: conventional roadways, parking areas
Fixture Placement: at the side
Ideal mounting height: The width of the road should not surpass 2.75 times the mounting height

Type IV

Pattern type: 60° semicircular distribution
Applications: wide roadways, sides of walls, or buildings
Fixture Placement: at the side
Ideal mounting height: The width of the road should not surpass 3.7 times the mounting height

Type V

Pattern type: 360° circular distribution
Applications: roadways, center parkway islands, intersections, large parking areas
Fixture Placement: at or near the center
Equal light distribution at all angles

Type VS

Pattern type: 360° square distribution
Applications: roadways, center parkway islands, intersections, large parking areas
Fixture Placement: at or near the center
Equal light distribution at all angles is used where the light pattern has a more defined edge

Mounting Height Considerations

To determine the ideal beam angle for a fixture, you need to know the distance between where the light will be mounted and the area to be illuminated. A closer distance means that a wide beam is needed. A further distance means that a narrow beam is needed.