PPFD Map

How PPFD Map calculates its result

The map runs the same Lambertian point-emitter model as the Light Calculator, evaluated at every grid point rather than averaged over a canopy.

1. Emitter layout: each fixture is divided into up to 48 emission points, laid out along its bars or across its face, sharing the fixture PPF equally.
2. Beam shaping: the Lambertian exponent is n = ln(0.5) / ln(cos(beam angle / 2)); contributions past 1.2 times the half angle are dropped.
3. Point contribution: PPFD = (PPF per point / (2 pi / (n + 1))) x cos^n(theta) x cos(theta) / d squared, with d in meters.
4. Grid: sample spacing scales with the space, at the longer side divided by 12, clamped to between 3 and 6 inches. A 48 x 48 in space is sampled every 4 inches.
5. Wall reflection: edge PPFD is averaged per wall, scaled by wall reflectivity, then added back to each point in inverse proportion to the square root of its distance from that wall.
6. Uniformity (DU) is minimum divided by average. Coverage is the share of points at or above 200. The dead zone is the share below 100. CV is standard deviation divided by average.
7. Daily light integral: DLI = average PPFD x photoperiod hours x 3600 / 1,000,000.

PPFD is in micromoles per square meter per second (SI canonical: mol/m^2/s). PPF is in micromoles per second. DLI is in moles per square meter per day.

Worked example

Running the map at its own default inputs:

The heatmap is a rendering of these same grid values. Every number above is available as text so the result can be read without the canvas.

Reference values