How to Calculate Lumens Per Watt

LED Wattage for Replacing Existing Lighting

We hear this question all the time. The unfortunate reality is that looking at “watts” is the wrong way to shop when you are replacing your existing lighting. You need to focus on “lumens”. In the world of LED Lighting, a watt is consumed by the LED product, and light is produced. That light is called lumens. Some LED products are better at doing that than other products.

So, it is important to understand that not all LED products are equal in terms of how efficient they are at converting watts to lumens. In technical terms, we call this lumens/watt.

Replacing X Watts Metal Halide with LED

Let’s discuss a practical example. Let’s say you want to replace your 250-Watt Low Bay inside your warehouse. Our High Bay LED Fixtures are built to run between 130 and 160 lumens per watt. This means that for every watt consumed, they will produce 130 to 160 lumens.

Our 120-Watt UFO Low Bay produces 18,000 lumens. By contrast, a competitor’s low bay that uses older LED Chips is designed to run at 120 lumens per watt. This competitor’s Low Bay produces 12,000 lumens. To match the amount of light our low bay produces, you would need 125 Watts of power.

So clearly watts are a poor gauge to determine what you would use to replace an existing light source. If a customer called both companies and asked “How many watts do I need to replace a 250-Watt Metal Halide?”, we would say 100 Watts, and our competitor would say 125 Watts.

So when our customers ask us how many ‘Watts” I need to replace an existing light source, we always convert them to a discussion on lumens.

However, there is one large elephant in the room still left here that we need to talk about. And that is the discussion of efficiency. In the above example, our Low Bay Lights produce the same amount of light while consuming 25 fewer watts per unit.

This is important because this is 25 fewer watts that you are consuming and paying for on your electricity bill. Efficiency does matter because it means your electricity bill will be significantly less using the 100 Watts Low Bay Light than a 125 Watts Low Bay Light.

So as with the discussion above, there is a vast difference between LED products being offered on the market today.

Read the specifications and educate yourself on lumens. The fewer watts you consume saves you money, and the more efficient the light means it will produce more light using less energy than less efficient models.

Lumens Guidelines

Pay special attention to the lumens per watt of the LED fixture or retrofit. IT DOES MATTER. An LED fixture at 150 lumens/watt will consume far less energy than an LED product producing 100 lumens/watt. Not all LEDs are the same. (Remember, always buy on the lumens you need, never on the watts you think you need.)

To calculate lumens per watt, take the total number of lumens a product produces and divide it by the watts it consumes.

You can get rebates for both new fixtures and retrofit kits. Make sure they are DLC-qualified. That is the key to getting rebates with your utility company. You can check if a product is DLC-qualified on the DesignLights Consortium website.

Rebates for DLC Premium should be higher than rebates with DLC Standard. Your local utility company typically provides the rebates and sets the rebate amounts.  Check their website.

All DLC Products are warranted for at least 5 years.

All our LED Fixtures and Retrofit Lighting are either UL-listed or ETL Listed.

Replacing the light parts of an existing fixture with a Retrofit unit will not void the UL or ETL Listing of the fixture.

An ETL Listing is the same as a UL Listing. They perform the same test, and the certification is the same. The only difference is the company that performs the test.