The Difference Between ANSI Lumens and Lumens

Overview of this measurement of visible light

The lumen is a measure of light defined by the International System of Units (SI). It describes the output of devices that emit light visible to the human eye. While lumens pertain to all light-emitting objects, ANSI lumens are a slightly different way of measuring light specific to projectors.

What Is a Lumen?

Lumens measure the volume of light coming from a given source. While the newest "official" definition of a lumen is highly technical, it's easier to understand the slightly older meaning, circa 2018. It describes one lumen as the amount of light you'd get unobstructed from one common wax candle (this measure is called a candela). It's an oversimplification. For us non-scientists, it's good enough for... well, non-scientist work.

One important distinction is lumens measure light as it's emitted directly from its source. Lumens are therefore essential when selecting products like light bulbs. While the common wisdom is to shop for light bulbs based on wattage, it's better instead to look at lumens, or better yet, lumens compared to wattage. It will tell you how efficient the bulb is at converting electricity to light. For example, to provide the same light output (lumens), LED bulbs consume about one-tenth of the wattage compared to older incandescent bulbs.

What Is an ANSI Lumen?

ANSI lumens are similar to SI lumens as they're both measures of light output. However, ANSI lumens are generally considered more accurate, as the standard includes some specific conditions for measurement. When measuring ANSI lumens, the space is assumed to be 25°C, the source will be emitting a specific white light, and the result is based on an overall average of 9 measurements from different points.

But other conditions include the use of a matte screen, a limitation on the amount of light reflected off it, and the use of 16:9 dimensions for the projection. So the most crucial difference is that the ANSI lumen standard was designed to measure the output of projectors. 

How Do You Convert ANSI Lumens to Lumens

You can find the estimated (SI) lumen output of a projector by dividing its ANSI lumen output by between 0.04 and 0.06, depending on the manufacturer (who may provide this value). But it's important to note that doing so is a bit artificial, as they're measuring two different things. SI lumens are a more general representation of how bright a light source is, while ANSI lumens are how bright that light is when it makes its way out of the projector and onto a surface.

What to Remember About Lumens and ANSI Lumens

To sum up, you should be on the lookout for SI lumens when shopping for products like light bulbs and other "general" lighting products. But when you're in the market for a projector, make sure you're picking the correct number of ANSI lumens for the space where you'll be using it.

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