Lux and lumen

Lux and Lumen

• Lumen is (approximately) the amount of emitted(/received) light

...as a total. You can consider it as an amount of power - not the part that arrives at you, and not per area

...but it is already filtered/corrected for how much it is seen by the human eye

• Lux is lumen per area - amount of emitted(/received) light per area

specifically 1 lux = 1 lumen / m²

e.g. for a projector: its lumen figure, divided by the area of the screen you're shining on

as a single figure, it's the best indication of how bright something will look on a given area of screen/wall.

For reference:

• 0.1-1 lux is moonlight in its various forms
• 1-10 lux is approximately twilight
• 4-20 lux street lighting (varies regionally)
• 20-50 might be the darker part of a not very well lit room
• 50-100 lux is one or two moderate lightbulbs in a hallway or small living room
• 100 lux is a dark overcast day
• 30-300 lux: the amount of sunlight that typically makes it into room with windows to outside, varying with window size and wall reflections
• 300-500 lux are well-lit areas in offices, libraries, and such
• 1000 lux is a brightly lit TV studio, or a regular overcast day
• 10000lux-20000lux: outside areas on a bright day
• 30000lux is direct sunlight