Lighting & Photobiology
PPFD, DLI, spectrum, photoperiod, light response, measurement, fixture placement, and plant-light interactions.
Published lessons
These pages are organized here by subject. The permanent THC-ENC IDs remain stable behind the scenes even when a clearer display title is used.
Light as Photons: PAR and ePAR
Distinguish photon-based plant-light measurements from human-vision and energy measurements, and state the wavelength band used for every value.
PPF, PPFD, and Fixture Output
Separate total fixture photon output from photon density at the crop and use each metric for the decision it actually supports.
Daily Light Integral Calculation
Calculate DLI from constant or time-varying photon flux and identify errors caused by units, sampling, and wavelength-band mismatch.
Photoperiod and Total Daily Photons
Explain how photon dose and light-dark timing interact without reducing photoperiod biology to a DLI calculation.
Measuring Canopy Light Correctly
Design a repeatable canopy-light measurement procedure that controls sensor choice, orientation, geometry, timing, and canopy condition.
Light Maps and Uniformity Metrics
Create spatial light maps and report distribution with metrics that do not hide crop-relevant dark zones or hotspots.
Inverse Square Effects and Fixture Geometry
Use inverse-square reasoning only where its assumptions apply and explain how extended fixtures, overlap, reflectance, and canopy geometry alter distance effects.
LED, HID, Fluorescent, and Sunlight Comparisons
Compare light-source systems across spectrum, controllability, distribution, heat pathways, maintenance, safety, and crop delivery rather than by technology label.
Photosynthetic Response Curves
Interpret leaf light-response curves without treating a short-term single-leaf measurement as a whole-crop yield curve.
Light Compensation and Saturation Points
Define compensation and saturation operationally and explain why both depend on method, tissue, acclimation, and environment.
Photoinhibition and High-Light Stress
Distinguish regulated photoprotection from sustained photoinhibition and diagnose high-light injury using plant, environmental, and spatial evidence.
Phytochrome and Red/Far-Red Signaling
Explain red/far-red sensing as a reversible signaling system that regulates morphology and flowering without treating wavelength ratios as standalone crop recipes.
Cryptochromes, Phototropins, and Blue Light
Differentiate major blue-light receptor functions and evaluate blue-light treatments through dose, fraction, background spectrum, and crop response.
Green Light and Canopy Penetration
Explain why green photons can support photosynthesis and penetrate leaves and canopies differently without assuming that penetration guarantees superior crop efficiency.
Ultraviolet Radiation: Evidence and Safety
Separate UV-A, UV-B, and UV-C exposure, evaluate cannabis claims against dose-defined evidence, and prioritize worker controls.
Spectrum Effects on Morphology
Analyze spectrum-induced morphology as an interaction among absolute photon dose, spectral fractions, photoreceptors, genotype, stage, and environment.
Photoperiodic Flower Induction
Describe flower induction as genotype-specific perception of recurring light-dark cycles and separate induction, visible flowering, and later development.
Night Interruption and Light-Leak Risk
Audit the true dark environment and manage night interruption according to intensity, spectrum, duration, timing, recurrence, and genotype.
Intercanopy and Intracanopy Lighting
Evaluate supplemental lighting within or below the canopy by photon redistribution, crop architecture, safety, sanitation, energy, and replicated crop outcomes.
Lighting Energy, Heat, Efficacy, and Crop Response
Connect electrical input, photon delivery, thermal load, canopy interception, biological conversion, and saleable output in one auditable lighting-performance chain.