Lumens are not the wall
A higher lumen figure helps, but only against the light already on the surface. A 30W unit in a dim room can out-read a 100W unit aimed at a lit shop window. Start from the wall, not the lamp.
Ambient light sets the floor
Measure the light falling on the target surface at the hour you care about. A controlled interior needs little; a facade at dusk or a window in daylight needs the top of the range.
- Dim interior: low end of range
- Lit shop window: upper end
- Daylight or streetlight: often needs the maximum
Distance and image size
Throw distance and image size move together. The same unit gives a small bright image up close or a large dim one far away. Fix the size you need first, then size the power.
| Throw | Image | Power feel |
|---|---|---|
| 3-5 m | 1-2 m wide | Modest |
| 8-15 m | 3-5 m wide | Mid |
| 20 m+ | Large facade | High + long-throw lens |
Why bigger image costs more
Spreading the same light over a larger area lowers the brightness per square metre. Buyers routinely underestimate how much output a big image eats — then blame the unit.
A practical check
Ask the supplier for image width at your throw, not a maximum distance. The width is what you will actually see, and it is the honest number.
Summary
Pick the unit by the worst-case surface and the image size, then confirm the lumen figure covers it. A number quoted alone tells you almost nothing.
