About CanopyMath
CanopyMath helps home indoor growers and greenhouse hobbyists quantify light and air conditions around houseplants, seedlings, herbs and vegetables. The tools connect temperature, humidity, fixture output, canopy area and photoperiod to the physical quantities growers can compare and adjust.
Climate calculations
The VPD calculator evaluates saturation vapor pressure at the air and leaf temperatures, derives actual vapor pressure from relative humidity, and reports the deficit at the leaf. It uses the equation in FAO Irrigation and Drainage Paper 56. Michigan State University Extension explains how VPD affects greenhouse transpiration; the calculator's stage bands are displayed planning assumptions rather than universal crop limits. The VPD chart tiles the same equation across a temperature and humidity grid and adds a fifth, cited band: the 0.45–1.15 kPa greenhouse range from the University of Georgia's e-GRO Alert 7(24).
Light calculations
The DLI calculator multiplies PPFD by seconds of light per day and converts micromoles to moles, following Purdue Extension's daily-light method. The PPFD calculator estimates fixture photon output from wattage and efficacy, applies a user-selected utilization fraction, and divides by canopy area. Its efficacy ranges are grounded in the published Kusuma, Pattison and Bugbee comparison. Coverage solves the same relationship for area rather than intensity.
How the math is checked
Automated reference cases evaluate the FAO saturation-pressure equation at known temperature and humidity combinations, check Fahrenheit-to-Celsius conversion, reproduce Purdue's DLI factor, and exercise photon-output, coverage and energy calculations. They verify that the code continues to implement those equations; they do not measure a fixture, map light uniformity across a real canopy or test a crop response.
Limits of the model
PPFD and coverage are area averages. Hanging height, optics, walls, fixture age and canopy shape can create bright and dim zones that one utilization percentage cannot capture, so a calibrated meter and a grid of readings are stronger than a wattage estimate. VPD and DLI targets also vary by species, cultivar, airflow and setup. The tools do not size structural or HVAC systems and provide general growing guidance rather than professional agronomic advice.
Report a calculation problem
Email [email protected] with the calculator URL, all inputs and units, the displayed result and the result you expected. A link to the paper, extension publication or standard you used makes the difference easier to reproduce.