The approximate lux equivalent is derived by first calculating the surface area (in square metres) that an LED-strip installation will illuminate. Surface area is based on the LED strip’s beam-width and its distance from the surface being lit.
The total lumens produced by the installation are then divided by the area, to give the approximate illumination.
How we calculate surface-area
When working out the illuminated area, most lumen-lux calculators assume a single-point lightsource. Ours is slightly different.
We calculate the area based on a length of tape, rather than a point. We approximate this by adding a rectangular area (equal to your LED strip’s tape-length x the diameter of an imaginary single-point source) to the circular single-point area calculation.