Light Maps and Uniformity Metrics
Create spatial light maps and report distribution with metrics that do not hide crop-relevant dark zones or hotspots.
Educational reference · evidence, sources, and limits shown below
Create spatial light maps and report distribution with metrics that do not hide crop-relevant dark zones or hotspots.
Terms to know
- Grid
- Defined set of measurement coordinates over a crop area.
- Uniformity ratio
- A declared comparison such as minimum divided by mean; the exact formula must be stated.
- Coefficient of variation
- Standard deviation divided by mean, usually expressed as a percentage.
- Spatial interpolation
- Estimate between measured points; an analytical aid that does not replace adequate sampling.
Core science
A light map preserves location. Use a fixed coordinate system, consistent cell size, and a crop-relevant measurement plane. Include edges, corners, fixture seams, and known obstructions; a grid that samples only expected good areas is biased.
Mean PPFD alone can conceal a crop with damaging hotspots and unproductive lows. Report the raw grid plus minimum, maximum, median, mean, standard deviation or coefficient of variation, and a clearly defined uniformity ratio. Percentiles can be more stable than a single extreme when measurement density is high, but extremes still require investigation.
Comparisons require identical geometry and operating conditions. Mapping an empty room may commission the installation, while mapping a mature canopy evaluates a different optical system because leaves absorb, reflect, and redistribute photons. Version each map with fixture layout and canopy state.
Why this matters in cultivation
- Distribution often controls consistency more than the headline average. It affects morphology, transpiration, maturation, quality grading, irrigation demand, and risk of localized high-light stress.
- Maps support fixture spacing, dimming zones, crop placement, maintenance, and acceptance testing after changes.
Measure and record
Map identity
Room, bench, date, crop stage, fixture layout revision, and operator.
Grid geometry
Origin, spacing, dimensions, measurement plane, coordinate labels, and excluded areas.
Conditions
Dimming, channels, warm-up, curtains, wall reflectance condition, and sunlight status.
Statistics
Raw values, mean, median, minimum, maximum, standard deviation, CV, and stated uniformity formula.
Actions
Hotspot or low-zone investigation, adjustment, remap date, and crop-response verification.
Common misconceptions
Correction: Different distributions can have the same mean.
Correction: Multiple definitions are used; the formula and sampling scheme must accompany the number.
Correction: Interpolation can create visual certainty that the measurement grid does not support.
Evidence limits
Uniformity acceptance criteria depend on crop architecture, economics, fixture system, measurement density, and the consequence of local extremes. No single threshold is universal.
Related encyclopedia topics
- THC-ENC-105, THC-ENC-107-108, THC-ENC-111, THC-ENC-119-120, and THC-GROW-060.
Source notes
- Resource Innovation Institute (2021). LED Lighting for Cannabis Cultivation and Controlled Environment Agriculture: Best Practices Guide.
- Rodriguez-Morrison V., Llewellyn D., and Zheng Y. (2021). Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment. Frontiers in Plant Science 12:646020.
- THC Cultivation SOP Source Materials Packet v1.0 (project source, May 2026).
This lesson summarizes the source material and its evidence limits for education. Use direct measurement, controlled comparison, and the cited sources when conditions differ or a decision carries meaningful risk.