Lighting Calculations for Street Lighting and Sports Lighting

Lighting is an essential element for ensuring the safety, comfort, and functionality of outdoor spaces. Whether it is for street lighting or sports lighting, proper lighting calculations are necessary to determine the optimal number, type, and placement of luminaires to achieve the desired illumination levels and uniformity. In this article, we will explain the basic concepts and methods of lighting calculations for street lighting and sports lighting, as well as some of the factors and standards to consider.

What is Lumen, Lux, and Luminous Efficacy?

Before we dive into the lighting calculations, let us first understand some of the key terms and units used in lighting design.

Lumen (lm) is the unit of luminous flux, which measures the total amount of visible light emitted by a light source in all directions. For example, a 100-watt incandescent bulb emits about 1,600 lumens, while a 100-watt LED bulb emits about 10,000 lumens.
Lux (lx) is the unit of illuminance, which measures the amount of light falling on a surface per unit area. One lux is equal to one lumen per square meter. For example, a typical office has an illuminance of about 500 lux, while a sunny day has an illuminance of about 100,000 lux.

Luminous efficacy (lm/W) is the ratio of luminous flux to power consumption, which measures the efficiency of a light source. The higher the luminous efficacy, the more lumens a light source can produce with less energy. For example, an incandescent bulb has a luminous efficacy of about 16 lm/W, while an LED bulb has a luminous efficacy of about 100 lm/W.

How to Calculate the Number of Luminaires for Street Lighting and Sports Lighting?

To calculate the number of luminaires required for street lighting and sports lighting, we need to consider the following factors:

The target illuminance level and uniformity for the area to be lit, which depend on the type, purpose, and usage of the space, as well as the relevant standards and regulations. For example, according to the CIE (International Commission on Illumination) recommendations, the average horizontal illuminance for a residential street is 15 lux, while the average horizontal illuminance for a professional football field is 500 lux.

The dimensions and shape of the area to be lit, such as the length, width, height, and orientation of the street or the sports field.

The characteristics and performance of the luminaires, such as the lumen output, luminous efficacy, beam angle, light distribution, mounting height, tilt angle, and spacing.

The environmental and operational conditions, such as the ambient temperature, humidity, wind speed, maintenance factor, and operating hours.

The basic formula for calculating the number of luminaires for street lighting and sports lighting is:

N=n×F×UE×A×MF

Where:

N is the number of luminaires
E is the target average illuminance level (in lux)
A is the area to be lit (in square meters)
MF is the maintenance factor, which accounts for the depreciation of the luminous flux due to dirt, aging, and failures
n is the number of lamps per luminaire
F is the initial lumen output of each lamp (in lumens)
U is the utilization factor, which accounts for the fraction of the luminous flux that reaches the area to be lit

For example, suppose we want to light a rectangular football field with dimensions of 100 m by 70 m, with a target average illuminance level of 200 lux and a uniformity ratio of 0.7. We choose LED flood lights with a lumen output of 50,000 lm, a luminous efficacy of 100 lm/W, a beam angle of 60 degrees, and a light distribution of type III. We assume a maintenance factor of 0.8 and an operating time of 10 hours per day. How many luminaires do we need?

First, we need to calculate the area to be lit, which is:

A=100×70=7,000 m²

Next, we need to calculate the utilization factor, which depends on the light distribution, the beam angle, the mounting height, the tilt angle, and the spacing of the luminaires. There are different methods and tables to estimate the utilization factor, but for simplicity, we will use the following approximation:

U=beam angle×light distribution factor/360

Where the light distribution factor is 1 for type I, 1.5 for type II, 2 for type III, and 2.5 for type IV. For our example, the utilization factor is:

U=60×2/360=0.33

Then, we need to calculate the number of lamps per luminaire, which is:
n=luminous efficacy×power consumption/lumen output

For our example, the power consumption of each LED floodlight is 500 W, so the number of lamps per luminaire is:

n=100×500/50,000=1

Finally, we can plug in the values into the formula and get the number of luminaires:

N=1×50,000×0.33200×7,000×0.8=85

Therefore, we need 85 LED flood lights to light the football field with the desired illuminance level and uniformity.

Conclusion

Lighting calculations for street lighting and sports lighting are important to ensure the optimal lighting design and performance for outdoor spaces. By understanding the basic concepts and methods of lighting calculations, as well as the factors and standards to consider, we can achieve the best lighting solutions for our projects.

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