PLB & SCL2 Series – Port Lavaca, TX

If you’ve been shopping for lighting, it’s a guarantee that you’ve come across marketing materials stating a light’s lumen performance. Although this is one of the most popular industry-standard terms for highlighting a light’s performance, it’s only part of the story.

What are lumens?

Lumens are a measurement unit used to determine how much visible light is produced by a light source.

What are watts?

Watts are used to measure power. How many lumens a light source can produce is dependent on how much power is given to it. A portion of power sent into a light fixture is inevitably lost to inefficiencies of mechanical and electrical components. The more efficient the lighting system, the more the power is converted to light instead of heat.

Efficacy: Watts vs Lumens

What is System Efficacy?

Efficacy (measured in lumens per watt) is a measure of how efficiently a light turns the power (watts) into light (lumens). To better understand a light fixture’s true performance, we can use efficacy’s simple calculation.

Efficacy = Lumens ÷ Watts

(It’s important to use the lumens produced and the watts consumed of the system instead of the LED alone)

System Efficacy takes into account both the LEDs’ efficacy and the system’s inefficiencies. 

Additional factors considered in calculating system efficacy are:

By leveraging this formula, a light fixture’s real-world performance becomes clearer. Comparing the system efficacy number against the chart below will give you a good idea of the performance of a light, or if more information is required.

(The above table is for system efficacy. It is not uncommon for LED efficacy to be above 160 lm/W)

The above table shows that as you increase the system efficacy, the performance of the light increases to a point. Once the light reaches a sufficiently high system efficacy, the only way to further improve it is by sacrificing other areas of performance: such as uplight, glare, distribution, color temperature, etc. This threshold where a higher system efficacy doesn’t translate to higher performance is typically around 140 lm/W but varies from product to product.

Informed Buying

A system efficacy rating is one of a host of great metrics like BUG ratings, color temperatures, and optical distributions to measure a light’s performance. The best metric to use is called application efficacy, which focuses on putting light into a useful place. Application efficacy can be shown using lighting layouts where system efficacy along with third-party qualified photometrics (which include all of the above metrics) are considered.

At First Light, we use all of these tools to make sure you are purchasing the right light for your application and to help you wade through the underperforming products and unsubstantiated claims of some manufacturers.

Contact us today to learn more about system efficacy or to discuss a project lighting layout.