How to Calculate Luminous Efficacy: A Sample Calculation

Introduction: Luminous efficacy is an important parameter used to measure the efficiency of lighting systems. It refers to the amount of visible light produced by a light source per unit of electrical power consumed. A higher luminous efficacy indicates a more energy-efficient lighting system, as it produces more light with less energy consumption. In this article, we will discuss how to calculate luminous efficacy, and provide a sample calculation to illustrate the process.

What is Luminous Efficacy? Luminous efficacy is a measure of how efficiently a light source produces visible light. It is expressed in lumens per watt (lm/W), where lumens (lm) represent the total amount of visible light emitted by the light source, and watt (W) represents the amount of electrical power consumed by the light source. Luminous efficacy is an important factor to consider when evaluating the energy efficiency of lighting systems, as it helps to determine how much light a light source produces for a given amount of energy input.

Calculation of Luminous Efficacy: The formula to calculate luminous efficacy is as follows:

Luminous Efficacy (lm/W) = Total Luminous Flux (lm) / Total Power Input (W)

To calculate the luminous efficacy, we need to know the total luminous flux and the total power input of the lighting system.

Total Luminous Flux (lm): The total luminous flux represents the total amount of visible light emitted by the light source. It is typically measured in lumens (lm) and can be obtained from the manufacturer’s specifications or from photometric data for the specific light source.

Total Power Input (W): The total power input represents the total electrical power consumed by the light source. It can be calculated by adding up the power consumption of all the lamps or luminaires in the lighting system. This information can be obtained from the manufacturer’s specifications or by measuring the power consumption of the light source using a wattmeter.

Sample Calculation: Let’s consider an LED bulb that produces a total luminous flux of 1500 lumens and consumes 10 watts of electrical power. We can use the formula mentioned above to calculate the luminous efficacy.

Total Luminous Flux (lm) = 1500 lumens Total Power Input (W) = 10 watts

Using the formula: Luminous Efficacy (lm/W) = Total Luminous Flux (lm) / Total Power Input (W) Luminous Efficacy (lm/W) = 1500 lm / 10 W Luminous Efficacy (lm/W) = 150 lm/W

So, the luminous efficacy of the LED bulb in this example is 150 lumens per watt.

Conclusion: Calculating luminous efficacy is an important step in evaluating the energy efficiency of lighting systems. By understanding how to calculate luminous efficacy and using it as a parameter for selecting lighting products, we can make informed decisions to choose more energy-efficient lighting solutions for our homes, offices, and other spaces.