Lumens are probably one of the most important features on projectors. If you own a digital projector that doesn’t have enough lumens then you won’t be able to see a quality image, or the image at all.
*For a projector that is meant to display 4K content, you will want at least 2,500 ANSI Lumens.
Answer to how many lumens is good for a 4K projector
What is a lumen for projectors?
Before we talk about anything else, we will have to go over what a lumen is in the first place.
A Lumen is…
A lumen (shortened to lm) is a SI-based unit that is used to measure luminous flux (waves of an electromagnetic variety) that humans can see). The term lumen is used to measure brightness coming from a source of light regardless of what it is (eg. projector, sun, flashlight).
Lumens are to light as oz is to weight and fahrenheit is to heat.
When one uses the term lumen for projectors, they are telling you how brightly the projector’s image is.
For projectors though, not all lumens are the same.
ANSI Lumens vs Lumens
The term lumen tells you how bright the projector’s lamp is capable of projecting. But this is only half of the truth.
ANSI Lumens
ANSI lumens is a unit, as given by the ANSI (American National Standard Institute), that is used to measure the total amount of light put out by a projector – not only the lamp’s light output of it.
ANSI lumens measure the brightness of the brightest white the projector puts out. It’s measured by using the meter reading on projected white content. The area of the projected image is then split up into 9 different zones with a 2 degree or smaller light meter. Then, the average of the measurements is taken and the result is the ANSI lumen output of the projector. The number you get tells you the total brightness the projector is capable of projecting onto a projector screen.
The benefit of using ANSI lumens is that it’s a standard that manufacturers can use that gives consumers an idea of the total amount of brightness the projector gives out that is usable.
Some manufacturers (cheap ones) advertise their projector with a lumen output that is much higher than the ANSI lumen rating.
For a better understanding this equation will give you an idea of the ANSI lumen value if it’s not already given.
LED lumen value / 2.4 = ANSI lumens
Around 30 percent of the light source’s actual light will reach the screen because the light from the projector lamp greatly diminishes before it has time to reach the screen.
How do you know how many lumens you will need for a projector?
One may think the lumens of a projector is all one really needs to know if the projector is bright enough for them. The projector itself is only 1/2 of the equation – the projector screen must also be considered. The surface of the projector screen is just as important as the projector itself.
To get an idea of how bright the image is going to be one could use the Foot-Lamberts system.
ftL(Foot-Lamberts) system
ftL is the unit used to measure how much light should be reflected off movie screens in 1 ft by 1 ft areas.
This is the calculation that takes into account the image the projector creates and the screen as a whole and says if the image is going to be bright enough.
Impacts on the Foot-Lamberts system:
- Screen seize
- Screen gain
- Projector brightness
The more brightness the projector has the more light there will be in the system.
The screen size also impacts the system because the bigger the image, the more spread out the image is going to be.
Screen gain discusses the reflective properties of the screen itself. The more gain, the brighter the image is going to be.
Here’s a tool you can use to calculate foot-lamberts
https://toolstud.io/video/lambert.php
| ftL | Viewing |
| 0-15 | Not bright enough |
| 16-26 | Good for dark room |
| 27-39 | Good for low ambient light |
| 40-59 | Good for medium ambient light |
| 60+ | Good for high ambient light |