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Part 2 - Everything You Need To Know About Lumens

Last month, we learned a little bit about lumens. Today, we will be discussing the radiation of lighting. To better demonstrate that, we will need to borrow a balloon. 

Choose a large balloon, one that can be inflated to a 2 ft. diameter with a 1 ft. radius. Let's use our imagination and put a lit candle inside the Part2.jpginflated balloon. Since the candle is radiating light uniformly in all directions and the candle is at the center of balloon, then the inside surface of the balloon will be evenly illuminated at a value of 1 foot candle (fc). Since the definition of the lumen is 1 fc / sq. ft., the balloon surface square footage of the represents the lumens radiated by the candle.

For those that slept through high school geometry, the surface area of a 1 ft. radius sphere is 12.58 sq. ft. Those that did not sleep through geometry know this value as 4p. So, the light radiated by the single lit candle is 12.58 lumens. In perspective, the 800 lumen, 60 watt incandescent bulb produces about the same light output as about 65 birthday candles. The below figure summarizes the candle in the balloon.


Remember Part 1, when I was trying to redo my kitchen lighting? If you don't remember, click here and read more. The 8 watt LED light will provide the same amount of light as the older 60 watt incandescent bulbs. Now, several of the LED lights have been purchased and installed in the kitchen. With great expectation, the new lights turn on and wait… what? The light does not look anything like we remembered the 60 watt incandescent bulbs producing. What happened? 

Check back next month to find out what happened and we will discuss how the lights radiate in different directions.


Written by: Ron Hughes

Ron has been with the engineering department of Ericson for 14 years. He has previously worked at Hubbell and Square D Company. He has a degree in engineering from The Indiana Institute of Technology. Ron has been married to his wonderful wife, Sandy, for 43 years, and they have one son together. In his free time, Ron likes to spend time with his Golden Retriever and taking nature photography.

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