Luminaire Mounting Height for a Target Illuminance
The inverse of the point-illuminance tile: the mounting height that lands a target horizontal illuminance at a point, height = sqrt( candela x cos(angle)^3 / E ). A 1,000 cd source needs a 10 ft mount for 10 fc directly below. Solves for HEIGHT (the point-method-required-candela tile solves for the candela). A higher mount lowers the illuminance. Direct illuminance from one source, ignoring interreflection; the photometric file and the IES target govern.
Formula and source
mount_height = sqrt( intensity_cd x cos(angle)^3 / target_fc ), the inverse of E_fc = intensity_cd x cos(angle)^3 / mount_height^2; distance = mount_height / cos(angle).
Point-by-point (inverse-square and cosine) method for horizontal illuminance (IES Lighting Handbook / IESNA point method), solved for the mounting height, by name.
Audience
This tile is built for electricians and the adjacent professions in the Electrical group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.