Projector Brightness Calculator
How many lumens does the projector need? Pick a target in nits, lux or footcandles.
Projector brightness
Planning values — ANSI lumens vs marketing "LED lumens" differ, and real-world brightness depends on content and calibration. Verify with a demo.
How projector brightness works
Lumens is the total light a projector puts out. But "is it bright enough?" depends on the screen size, so the useful units are nits (luminance — how bright the image looks) and lux / footcandles (illuminance — how much light falls on the screen). They convert through the screen area:lumens = nits × area(m²) × π ÷ gain,lumens = lux × area(m²), andlumens = fc × area(ft²).
Gain only enters the nits formula. It measures how much the screen reflects light back to the viewer (1.0 is a neutral matte white; higher gain is more directional and brighter on-axis). Lux and footcandles describe the light hitting the surface, so a screen's gain does not change them. The same lumens therefore express as different numbers in each unit — this calculator shows all three so you can compare a spec sheet written in any of them.
Worked example
A 120″ 16:9 screen is about 3.97 m² (42.73 ft²). To hit 50 nits (a dark cinema room) at gain 1.0 you need 50 × 3.97 × π ≈ 624 lumens — so you would buy a1000-lumen projector. At gain 0.8 the requirement rises to ≈780 lumens. The same 624 lumens is equivalent to about 157 lux or 14.6 footcandles.
Frequently asked questions
What is the difference between lumens and nits?
Lumens is the total light a projector emits; nits (cd/m²) is the luminance — how bright the image actually looks, which depends on the screen area and gain. A small screen looks brighter than a large one for the same lumens.
What is the difference between lux and footcandles?
Both measure illuminance — light falling on the screen. Lux is lumens per square metre; a footcandle is lumens per square foot. 1 footcandle = 10.764 lux.
Why does gain affect nits but not lux?
Gain is how much the screen reflects light back toward the viewer, so it changes luminance (nits). Lux only measures the light hitting the screen surface, regardless of how reflective that surface is.
What brightness do I need?
As a starting point: 50 nits for a dark cinema room, 150 nits for a dim room, 300 nits for a lit room, and 500 nits for a bright space. Reduce these if the room is fully light-controlled.
Are ANSI lumens the same as LED lumens?
Not always — marketing "LED lumens" can be inflated versus the ANSI standard used for traditional lamps. Treat every figure as a planning value and confirm with the projector’s real-world reviews or a demo.
Related calculators
- Display Setup Simulator — the full plan: viewing distance, brightness and room layout.
- Projector Throw Distance Calculator — where the projector sits for a given screen.
Disclaimer: brightness figures are planning estimates. Confirm real-world output, ANSI lumen rating and calibration with your projector manufacturer.