Lumens to Watts Conversion Chart - Never Buy Based on Watts

This is a common message we try to impart to our customers when they call us. For example, it is not uncommon for us to get a call to quote a price on high bays and be told they need a price on a 150-Watt LED Fixture. The most important thing we can do for our customers is to explain LED efficiency. Read this post to discover the right way to pick the right LED product.

What are Watts?

Watts are simply a measurement of energy consumption. When you pay the utility bill, the bill represents a charge for the number of watts of energy you used. A 400-Watt metal halide shop light consumes 400 Watts of energy. What it doesn’t represent is the amount of light, or lumens, produced. Although, over time, we begin to associate light levels with the bulb being used. So, we say “We want the brightness of a 400-Watt metal halide bulb”. What we really are discussing is the amount of visible light produced by the bulb, which consumes 400 Watts.

What are Lumens?

Put simply, a lumen is a measurement of visible light. The more lumens you have, the brighter the light will appear. Most companies will tell you three important facts about lumens.

• Initial Lumens: How many lumens will the fixture produce when it is brand new?
• L70 Lumens: How many hours will it take before the fixture only produces 70% of the initial lumen value?
• The lifetime of fixture: This is typically the expected life (before complete failure) of the fixture, or how long you can expect the fixture to operate without the need for maintenance.

Understanding Lumens/Watt or Efficacy

The key to this discussion is understanding lumens per watt or efficacy.  This is a measurement of how efficiently a light source converts watts into lumens. Old technologies like metal halide have an efficiency of about 80 lumens per watt. So, it takes 400 watts to produce 32,000 lumens.

However, here’s the catch. Not all LED products have the same efficiency. In fact, the variance can be rather dramatic.

• An LED fixture at 100 lm/W needs 200 watts to produce 20,000 lumens.
• A more efficient LED at 150 lm/W needs only 133 watts to produce 20,000 lumens.

So, when buying LED, it’s really important to understand the efficacy of the fixture when comparing products.

How to Determine the Best LED Fixture That Consumes the Least Amount of Energy

So, let’s say you are in the market to replace your existing lighting. Here are the steps to follow.

• Determine how many lumens you need. How do you do this? Take a foot candle reading at your location and determine if that is the right amount of light.
• Now that you know the average foot candles, determine how many lumens you need to produce this amount of light to meet your foot candle requirement. A reputable company, such as LED Lighting Supply will assist you by using photometrics and show you, by using specialized software, how the light levels could look when you convert to LED.
• Pick the fixture with the highest efficacy to produce those lumens. The watts consumed by the fixture is the amount of energy consumption that you will have.

Buy Cheap. Buy Twice.

Let’s make one point clear, we are very competitive with our pricing. But we get a lot of customers calling us to fix their cheap LED purchase problems (purchased elsewhere). A cheap product is typically inefficient and has a low lumens/watt efficiency.

Those problems consist of lights that have broken or aren’t what customers thought they were buying. So, we understand that everyone wants a bargain. But be careful of low-priced products – it’s cheap for a reason.