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Understanding ANSI Lumens and Other Brightness Units for Projectors

ANSI Lumens, Lumens, Nits, Foot-Lamberts, and Lux

2025/05/08

As consumers become more informed and online shopping becomes the norm, understanding tech specs is more important than ever—especially for projectors, where prices, features, and performance can vary a lot. Of all the specs, brightness tends to cause the most confusion.

Projector brightness is measured in several different units—lumens, lux, foot-lamberts, nits, and ANSI lumens. Knowing how they differ can help you make smarter, more confident choices. While “brightness” is the common term, it’s actually subjective. In optical terms, the more accurate word is “luminance.” But for clarity, we’ll stick with “brightness” throughout this article.

Table of Contents

What are ANSI Lumens, Lumens, Nits, Foot-Lamberts, and Lux?
Lumens vs. Nits: What Really Affects Image Brightness?
How to Choose the Right Projector Brightness for Your Room?

What are ANSI Lumens, Lumens, Nits, Foot-Lamberts, and Lux?

These are the most commonly used units to describe brightness in the projector world—but they’re not always easy to understand. Below is a quick breakdown of what each one means and how they differ.

Want to skip the technical stuff and go straight to how to apply this when choosing a projector? Feel free to jump ahead to the Choose the Right Projector Brightness section.

ANSI Lumens

ANSI Lumens is a unit, defined by the American National Standards Institute (ANSI), that measures the overall amount of light output by a projector, in other words the higher the lumen value for a projector the brighter the light it produces.

Lumens

Lumen (lm) is the SI-based unit that measures luminous flux, in other words the total amount of light produced by a light source per unit of time. Luminous flux as a measurement is different than radiant flux because luminous flux measures only the electromagnetic waves that the human eye can see while radiant flux measures all electromagnetic waves emitted by a source.

Nits

Nits is a unit that measures brightness in terms of area, or in technical terms, candela (a standard unit of light equivalent to the light produced by a single candle) per square meter.

Foot-Lamberts

Foot-Lamberts, or ft-L, takes the same unit of light used in defining nits, the candela, but applies it to the unit of area customary to the United States, square feet, meaning that 1 ft-L is equal to 1 candela per square foot.

Lux

Lux is similar to nits and ft-L in that it also measures brightness in terms of surface area, but in this case, it is defined as lumen per square meter.

Lumens vs. Nits: What Really Affects Image Brightness?

Lumens (Light Output) vs. Nits (Brightness on Screen)—these two terms are often used when talking about projector performance, but they describe very different things.

．Quick Comparison: Lumens vs. Nits

Unit	What It Measures	What It Tells You
Unit Lumens	What It Measures Total light output from the projector	What It Tells You How much light the projector emits overall
Unit Nits	What It Measures Brightness per unit of screen area (cd/m²)	What It Tells You How bright the image actually appears on screen

Unit

What It Measures

What It Tells You

Unit

Lumens

What It Measures

Total light output from the projector

What It Tells You

How much light the projector emits overall

Unit

Nits

What It Measures

Brightness per unit of screen area (cd/m²)

What It Tells You

How bright the image actually appears on screen

Lumens measure the total light output from a projector—but that doesn’t reflect how bright the image actually appears. We don’t look directly at the light source; we see the light reflected off the screen, and the size of that surface matters. For example, projecting onto a 1 square meter screen looks ten times brighter than projecting the same light onto a 10 square meter screen.

That’s why lumen ratings only tell part of the story. Nits, on the other hand, measure brightness per unit of area. This makes it much easier to compare how bright the image actually looks—so a 300-nit image is, by definition, brighter than a 100-nit one.

How to Choose the Right Projector Brightness for Your Room?

Now that we know lumens alone don't tell the full story, how do you actually choose a projector with the right brightness? Brightness on screen can be affected by many other factors—like ambient light, image size, and color accuracy. If you want a clearer picture of how all these elements work together, this article breaks it all down.

Start by identifying the ambient lighting in your space and finding the corresponding minimum screen brightness (in nits) from the table below.

．Ambient Lighting and Minimum Brightness Requirements

Ambient Lighting Environment	Example Setting	Recommended Image Brightness (nits)
Ambient Lighting Environment Dark Room	Example Setting Lights off at night	Recommended Image Brightness (nits) 50 nits
Ambient Lighting Environment Dim Room	Example Setting Soft lighting at night	Recommended Image Brightness (nits) 100 nits
Ambient Lighting Environment Lit Room	Example Setting Daylight, no direct sunlight (Home Theater)	Recommended Image Brightness (nits) 200 nits
Ambient Lighting Environment Bright Room	Example Setting Indirect daylight, TV viewing	Recommended Image Brightness (nits) 300–400 nits
Ambient Lighting Environment Outdoors	Example Setting Indirect sunlight	Recommended Image Brightness (nits) 600+ nits

NOTE: You can convert nits to foot-lamberts (ft-L) using this converter.

Once you’ve figured out the ideal nit value, match it with your screen size in the chart below to estimate how many lumens your projector needs to deliver that brightness.

．Recommended Projector Brightness by Image Size

Example: If you want a 100-inch image in a bright room (300 nits), you’ll need a projector with at least 3100 lumens.

Now that you know your screen size and lighting conditions, you're now ready to choose a projector that matches your actual viewing needs—not just what the spec sheet says.

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Buying Guide

Before you wrap up, here’s one last thing to watch out for when comparing projector specs:

The Myth of High Light Source Brightness

There sometimes is a misconception among consumers that the lumen value for a projector’s light source is the same as the lumen value for the projector. In reality the light from the projector’s light source diminishes quite a bit before it is even projected, since it’s transformed by the projector’s imaging mechanism as it passes through projector. What this means is that on average the ANSI lumen value of the projector itself is usually only about 30% of the lumen value of its light source, so that a projector with a 3,000-lumen light source might actually only produce 900-lumen light. But some brands only list the brightness value of their projector’s light source so as to trick the consumer into mistaking one for the other and thinking that their projectors are brighter than they really are, which is something that consumers need to be aware of.

Introduce BenQ CinematicColor technology for accurate colors.

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True colors evoke feelings of sorrow, joy, romance and thrills by preserving the original image. BenQ home cinema projectors embody our belief to “Convey the truest color and impart the deepest feelings to the viewer.”

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