ANSWERS — HOW IT COMPARES
LED or HPS: how should you light a greenhouse crop?
Grow lights come from lighting manufacturers, not from us — but the fixture choice reaches into your electrical service, your climate budget, and your irrigation schedule, so it has to be planned with the building. Here is the honest comparison.
AMERICAN ROOTS — ANSWERED BY THE PEOPLE WHO BUILD IT · UPDATED JULY 2026
01 — THE NUMBER THAT MATTERS IS DLI, NOT WATTS
Spec to the light integral, not the number on the fixture box.
Daily Light Integral — the total light a canopy receives in a day — is what actually drives yield. A fixture's instantaneous output (PPFD) is meaningless without run-hours: hitting 20 mol of DLI over a 16-hour day takes a sustained ~347 µmol of PPFD, and a short blast of high PPFD can deliver less DLI than moderate light run longer. Trade sources put cannabis targets at roughly 35–45 mol DLI, with flower-canopy PPFD approaching 1,000 µmol.
35–45 MOL DLI
CITED CANNABIS DAILY-LIGHT TARGET — THE NUMBER FIXTURES ARE SIZED AGAINST (TRADE SOURCES)
02 — THE EFFICIENCY COMPARISON
LED moves the same light for roughly half the electricity.
| MEASURE | LED | HPS |
|---|---|---|
| Efficacy (µmol/J) | ~2.7–3.0 | ~1.7–2.1 |
| Electricity for the same canopy light | ~40–50% less (lighting-supplier figures) | baseline |
| Radiant heat at the canopy | Lower | Higher |
| Cited lifespan | More than twice HPS | baseline |
VENDOR AND TRADE FIGURES, ATTRIBUTED — DIRECTIONAL, NOT A QUOTE FOR YOUR ROOM
LEDs are also cited at around 60% of the greenhouse lighting market, with energy savings of 40 to 60% versus HPS. A peer-reviewed study found supplemental greenhouse lighting increased water-use efficiency, crop growth, and cutting production in Cannabis sativa — the payoff is real, not just vendor talk.
03 — THE TRADEOFF NOBODY PUTS ON THE SPEC SHEET
Switching to LED is a cultivation shift, not a bulb swap.
HPS bathes the canopy in radiant heat; LEDs mostly don't. Move to LED and leaf temperature drops, which changes your VPD and forces the irrigation schedule to be re-tuned. Budget the transition as a growing-method change: the fixtures are the easy part, the climate and watering recipes are the work.
04 — WHAT IT MEANS FOR THE BUILDING
Lights are the biggest single electrical load — plan the building around them.
Grow lighting is the line that most often blows up an undersized electrical service or generator, and every watt of light is also a heat and VPD decision inside the envelope. Size the electrical service to the fixture plan before the pad is poured, and size backup power last, from the total simultaneous load. The rest of the fit-out picture: what equipment you'll add beyond the greenhouse.
PLAINLY
Buy fixtures from a lighting manufacturer, sized to a DLI target — not a wattage. Then tell us the load, so the building, its service, and its climate plan are designed for the light from day one.
Does American Roots sell grow lights?
No — fixtures come from lighting manufacturers. We design the structure and plan the electrical and climate implications with you, and our book prices the building itself live in the build tool.
How much lighting does a cannabis greenhouse need?
Trade sources cite roughly 35–45 mol DLI with flower-canopy PPFD near 1,000 µmol, but the fixture count depends on your glazing, latitude, and photoperiod — spec to the DLI target with your lighting supplier, not to wattage.
Is LED really cheaper to run than HPS?
The cited efficacy gap — roughly 2.7–3.0 µmol/J for LED versus 1.7–2.1 for HPS — works out to about 40–50% less electricity for the same canopy light, with more than twice the lifespan. The catch is the lower radiant heat: your VPD and irrigation schedules need re-tuning after the switch.
Plan the light. We'll build the building that carries it.
Price the structure in the build tool, then bring your DLI target — a Greenhouse Expert plans the service, climate, and backup implications with you.
WIDTH — 30 FT MODULES
OR TALK TO A GREENHOUSE EXPERT — (772) 321-6305