Is There a Difference Between ANSI, Light Source, and LED Lumens?

In the projector market, the most commonly used measures of brightness are ANSI Lumens, Lumens from light source, and LED Lumens. Though each method uses lumens – the standard brightness unit in the field of optics – as their basic unit of measure, they differ intrinsically in what they are actually measuring.

ANSI Lumen is the measure of the brightness of the light from a projector as defined by the American National Standards Institute (ANSI). It is typically measured by taking several brightness readings (in lumens) from various points on a projector’s white screen at a given distance and averaging them to determine the value.

Light source Lumen or brightness, as its name denotes, refers to the measured light output of a projector’s light source, which depending on the type of projector may be a lamp, LEDs, or lasers. Light source brightness differs from ANSI lumens in that ANSI lumens measures the brightness of the light projected by the projector (meaning the light that has undergone the imaging process of the projector), while light source brightness measures its brightness directly from the light source itself before it has been converted to an image by the projector’s other components.

LED Lumen is a measure of brightness used by some manufacturers of LED projectors that takes into account what is known as the Helmholtz–Kohlrausch (HK) effect. The HK effect refers to the phenomenon whereby the human eye views highly-saturated colors as brighter than they objectively are. With the HK effect in mind, LED brightness acts as a value that tries to quantify, in actual lumens, the added brightness that results from the improved color performance of LED lights.

Given the almost inconsistent way each of these brightness values are used in product advertising, how then do we make sense of them and how they relate to each other? Can one value be directly compared to another? To start the discussion off we must first recognize that ANSI lumens is by far the most consistent and reliable brightness value used, as it is a standardized measure agreed upon by an internationally-recognized organization. From there, we can then discuss the other types of brightness measures in relation to ANSI lumens to understand how they are calculated for a deeper understanding of all of them.

Bluntly stated, brightness values of light source are always higher than ANSI lumen values. This is because, by definition, their calculations do not factor in any of the loss of brightness that occurs within the projector due to the imaging process. Their numbers are thereby free from the deflationary effects that the inner workings of the projector have on its brightness value (for example the percentage drop caused by the color wheel). Because of this, the light source lumens of a projector may be greater than the value of its ANSI lumens by a large factor.

ANSI Brightness = (L1+L2+L3+L4+L5+L6+L7+L8+L9)/9 (lux) x A (m^2)

A (Area) = W * H (m^2)

In terms of a raw comparison of numbers, the LED lumen value for a projector is also always higher than its ANSI lumen. This is because, as discussed earlier, LED lumen measures seek to incorporate the additional brightness that results from the HK effect.