Point-Method Required Candela for a Target
The inverse of the point-illuminance tile: the luminous intensity a fixture must aim toward a point to hit a target illuminance, I = E x mounting-height^2 / cos(angle)^3 (E in footcandles, lux / 10.764). Hitting 10 fc from 10 ft up straight below needs 1,000 cd; the same 10 fc at a point 30 deg to the side needs about 1,540 cd (the cos^3 penalty off-nadir). Answers 'what candlepower do I need' instead of the illuminance from one fixture. Direct component only; the photometric file and the IES target govern.
Formula and source
E_fc = target (lux / 10.764); required intensity I = E_fc x mount_height^2 / cos(angle)^3. The inverse of E_fc = I x cos(angle)^3 / mount_height^2.
Point-by-point (inverse-square and cosine) method solved for the luminous intensity, IES Lighting Handbook / IESNA point method, by name.
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