# Light-distribution mapping

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A polar and position-indexed method for measuring spectrum, PPFD, DLI and temporal exposure in the rotating geometry.

In brief

A polar and position-indexed method for measuring spectrum, PPFD, DLI and temporal exposure in the rotating geometry.

## Measurement grid

Measure at every cultivation position or at a justified symmetric subset covering axial level, angular position and radial plant plane. Record the detector orientation and distance from the central source.

## Required conditions

 |
 Condition | Measurement

 | Rotor static | position-by-position PPFD and spectrum
 | Rotor operating | time-resolved exposure or rotation-integrated measurement
 | Empty system | optical baseline
 | Representative canopy | self-shading and reflection effect
 | Thermal steady state | light output and leaf-temperature stability

## Uniformity statistics

 L-2 C V P P F D = 100   s P P F D P P F D ‾ \mathrm{CV}_{\mathrm{PPFD}}=100\,\frac{s_{\mathrm{PPFD}}}{\overline{\mathrm{PPFD}}} CV PPFD ​ = 100 PPFD s PPFD ​ ​ Position-to-position coefficient of variation.

**Explanation**This measures how uneven the light map is. A lower percentage means the measured positions receive more similar light.

 L-3 U min ⁡ / m e a n = P P F D min ⁡ P P F D ‾ U_{\min/\mathrm{mean}}=\frac{\mathrm{PPFD}_{\min}}{\overline{\mathrm{PPFD}}} U m i n / mean ​ = PPFD PPFD m i n ​ ​ Minimum-to-mean uniformity ratio.

**Explanation**The darkest measured point is divided by the average. A value closer to one means better minimum-to-average uniformity.

## Published output

The calibration report contains the raw grid, polar heat map, spectrum, measurement uncertainty, detector model, light state, system geometry and DLI calculation. A single centre-point value is insufficient.

## Spectral scope

The mapping protocol records the measured spectrum and includes far-red photons separately where present. [R33]

## References

- [R33] Zhen, Shuyang; Bugbee, Bruce (2020). Far-red photons have equivalent efficiency to traditional photosynthetic photons: Implications for redefining photosynthetically active radiation. *Plant, Cell & Environment, 43, 1259–1272*. https://doi.org/10.1111/pce.13730