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+1 (813) 649-8899Comparing IESNA and NEMA Light Distributions
Beam spread is one of the most important yet misunderstood factors to consider when determining the right fixture for the job. After all, a spotlight would not provide the same wash of light as a parking lot fixture, even with the same wattage and lumen output. Thankfully, light distribution has already been categorized in two different ways, IESNA and NEMA. With different metrics, classifications, and applications, both of these are crucial tools for deciding the lighting application between different light fixtures.
What are IESNA and NEMA Light Distributions?
IESNA and NEMA are two of the most common categories of light distribution used in the United States.
IESNA, which is short for Illuminating Engineering Society of North America, is typically used for street and area lighting, and typically classifies light distribution by the general shape of the light spread.
In contrast, NEMA, short for National Electrical Manufacturers Association, focuses instead on the beam angle and is used more commonly with floodlighting, spotlighting, and other general purpose lighting applications.
Types of Beam Light Distribution in IESNA & NEMA Standards
The following table can be used as a general guide to illustrate the differences on light distribution between and even within IESNA and NEMA categories:
| IESNA Beam Distributions | |
 Type I |
Ideal for lighting narrow paths and walkways, this is placed in the center of a pathway for symmetrical and bi-directional lighting with a lateral distribution up to 15 degrees. |
 Type II |
Used in wider walkways and jogging paths, these have a lateral width of 25 degrees and can be used to light road widths up to 1.75 times the mounting height. |
 Type III |
Meant to be used in general roadway lighting, parking lots, and other larger area lighting applications, the forward throw is longer than Type II with a shorter side throw. These have a preferred lateral width of 40 degrees and an asymmetric distribution to light up to 2.75 times the mounting height. |
 Type IV |
The best option for perimeter and wall-mounted area lighting, these provide a more rounded asymmetric distribution than Type III with a greater and more intense forward throw. This added intensity allows for lighting wider roadways up to 3.7 times the mounting height and has a preferred lateral width of 60 degrees. |
 Type V |
With 360 degree circular distribution and equal intensity throughout, Type V is ideal when mounting centered in parkway islands, intersections, and other central locations requiring a wide are of lighting. |
 Type VS |
Like with Type V, this provides 360 degrees of even light distribution. However, the distribution is square to provide more defined and uniform lighting in large commercial areas. |
As you can see, the applications for IESNA light distributions can vary widely based on the shape of the throw, before accounting for other factors such as mounting height and lumen output. For example, our LED Parking Lot Light Fixtures are all Type III Distribution, which has a longer forward throw but narrower side to side throw than Type II and can be used in general parking areas.
| NEMA Beam Distributions | |
 Type1 - Very Narrow10-18 Degree |
With a tighter beam angle, these are ideal for lighting taller or farther setbacks, such as flagpoles and taller trees |
 Type 2 - Narrow18-29 Degree |
|
 Type 3- Medium Narrow29-46 Degree |
With a wider beam angle, these provide enough balance between setback distance and beam spread, and are best used in accent lighting, such as for landscaping and sign lighting |
 Type 4 - Medium46-70 Degree |
|
 Type 5 -Medium Wide70-100 Degree |
|
 Type 6 - Wide100-130 Degree |
Wider distributions typically work best with shorter setbacks and cover a much wider space, including general landscape lighting and can be used in pole mounting for general area lighting |
 Type 7 - Very Wide130+ Degree |
|
With NEMA, the distribution has been simplified to the degree of the beam angle, and can be measured vertically and horizontally. Our LED Flood Lights are available in several different distributions for different applications, such as our LED Bullet Flood Lights in either 22 or 57 Degrees both vertically and horizontally which means these are NEMA Rated 2H2V Narrow Beam and 4H4V Medium Beam distributions for flagpole and landscape lighting, respectively. Additionally, our LED Slim Flood Lights are rated as 7H7V Very Wide Beam, perfect for monument sign lighting and other applications requiring a wide wash of light.
Conclusion
HTM Lighting Solutions specializes in providing photometric layouts using both IESNA and NEMA beam distributions to provide optimal results. By understanding the lighting application for a particular fixture, we maximize the efficiency of our lighting without risking glare or dimly lit areas. Please feel free to reach out to us for a lighting layout or quote for any of our products, either by giving us a call at (813) 649-8899 or sending over an email at sales@htm-lighting.com.
- Michael Tomas
