Illuminance Uniformity of Street Light: How to Measure And Improve

Illuminance Uniformity of Street Light How to Measure And Improve

Illuminance uniformity is one of the light distribution characteristics of street lights. If the light distribution design is not reasonable enough, it will lead to uneven light. That is, when you look at the roads, you find there are darker places, or even worse, places that haven’t been illuminated. This kind of lighting is dangerous and likely to cause accidents. How do I know if the street lighting is uniform enough and improve the illuminance uniformity? Check out this article to learn more about it!

What is illuminance uniformity?

Illuminance uniformity measures if the lighting of a certain area is uniform enough to the area besides it. The larger the difference, the worse. If the areas are not uniform enough, drivers cannot see the road condition clearly, and the bright area will generate glare. Moreover, it may cause eyestrain, which has a negative impact on drivers when they have to drive for a long time.

Illuminance uniformity is different from average illuminance. Average illuminance detects the value of the brightness of a whole area, while illuminance uniformity compares one area with another.

How to measure the uniformity of illuminance?

The uniformity of illuminance is usually abbreviated as U0. As for some special areas like the stadium, the uniformity requirement is higher, so it is calculated as U1. The minimum illuminance is Emin, the maximum illuminance is Emax, and the average illuminance is Eave. U0 equals Emin/Eave, and U1 is the ratio of Emin and Emax.

While measuring, there are requirements for the roads detected. The road that is representative in the distance of lights, height of the light, installation parameters such as overhang and elevation, etc. is the best choice for detection.

Standards of illuminance uniformity

If the illuminance uniformity is close to 1, this lighting has the best lighting performance because it will make any place on the road look almost the same, thus making drivers feel comfortable. If it can’t be 1, then the smaller the value, the better.

Although there are different types of roads, the standard value of U0 is the same.

For highway lighting, no matter if it is the main road or a branch road, the U0 should be at least 0.4.

For intersection areas that connect the main roads and branch roads, the value of U0 should be 0.4.

intersection areas

Factors that affect illuminance uniformity

Light source location

A reasonable light source location can prevent uneven illumination caused by too strong or too weak light.

Lamp shape

The design of lens and lampshade should avoid producing too strong a light beam in a certain direction, resulting in too strong or too weak illuminance distribution.

The number and layout of light sources

Reasonable layout and quantity adjustment can avoid excessive fluctuations in illuminance and uneven light brightness and make the road surface’s illuminance uniform.

Road surface reflectivity

The higher the road surface reflectivity, the more light emitted by street lamps will be reflected on the road surface, and the better the uniformity of illumination.

Ways to improve illuminance uniformity

Reasonable lamp design

In the design of LED street lamps, uniformity of illumination should be given priority. Within the diameter range covered by street lamps, the distribution of illumination should be more uniform, and the size of the gradient of illumination should be reduced.

Point height of street lights

The point height of street lights refers to the distance between the street lights and the road surface. Different roads and application scenarios will require different spot heights for street lights. For short streets, the spot height of street lights should be appropriately reduced, while in spacious venues and squares, the spot height of street lights can be slightly higher.

Road surface reflection

Road surface reflectivity is one of the most important factors affecting the uniformity of illumination of LED street lights. Therefore, the reflectivity of the road surface should be improved. The light radiation of the reflected light on the road surface should be reduced to improve the uniformity of the illuminance distribution.

good uniformity of illuminance

In a way that also saves energy

For the sake of saving energy, several cities adopted the solution of lighting one street light and then closing the one next to it. Although it may alleviate the lack of electricity, there is no doubt that both the illuminance and the uniformity of the illuminance have largely decreased. One example is Japan in the 1970s, when the world was in an energy crisis. Applying this solution has had a negative effect on the safety of passersby and led to more accidents.

So how should we set the street light to save energy and at the same time ensure its illuminance and uniformity? One way is a staggered or symmetrical arrangement. If you choose street lights that have a reasonable light distribution design, even if you turn off several lights at night, the uniformity can still remain at the standard level. Note that you have to consider the width of the road, the traffic on the road and the roadside, and so on, to decide when you can apply this solution.

On expressways or main roads where there is a high requirement for illuminance and the road is relatively wider than others, there is another solution. That is, setting two light sources on the same pole. You can turn on both lights when the night comes, and at late night turn off one of them. In this way, it barely has any influence on the uniformity of the illuminance.


The uniformity of illuminance is an essential value among the light distribution characteristics. It is related to the safety of drivers and passersby. Factors like the light distribution design, height of the light, lamp shape, and the roads will influence how uniform the illuminance can be. The best way to ensure uniformity of illuminance is to choose a reliable LED street light manufacturer. Street lights produced by Mokolight all have a certified uniformity and are also outstanding when it comes to other features. For 16 years, Mokolight has accumulated experience in manufacturing and improved the quality and efficiency of production.

Written by ——
Scott Hughes
Scott Hughes
Double Bachelor's degrees in Architecture and Electrical Engineering, 5+ years of experience with LED lighting, intelligent moving lights, and conventional fixtures
Scott Hughes
Scott Hughes
Double Bachelor's degrees in Architecture and Electrical Engineering, 5+ years of experience with LED lighting, intelligent moving lights, and conventional fixtures
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