What Is a Photometric Light Plan, and Why Get One Before You Buy Grow Lights?
The most expensive lighting mistakes in a commercial grow are made before anything is installed: too few fixtures and a dim canopy edge, too many and a power bill you didn't budget for, the wrong voltage for the building, or a model that doesn't qualify for the rebate you were counting on. A photometric light plan catches these on paper.
Here is what a plan is, what it should show you, and what to send so you get one back quickly.
What a photometric light plan is
A photometric plan is a computer model of your room. It takes the measured light distribution of a specific fixture, usually from its IES photometric file, places that fixture in your room at a set spacing and hang height, and calculates the PPFD that reaches every point of the canopy. The result is a heat map and a set of numbers you can compare across options before you spend anything.
The point is to answer "how many fixtures, and where?" with numbers rather than a rule of thumb.
What a good plan shows
Fixture count and layout: how many fixtures, the rows and spacing, and where they sit relative to benches, racks and walkways.
Hang height: the distance from fixture to canopy that the numbers assume.
PPFD map: a grid of values across the canopy, not just a single number for the centre.
Average, minimum and maximum PPFD: the average tells you whether you hit your target; the minimum shows the weak edges and corners.
Uniformity: usually the minimum divided by the average. The closer to 1, the more even the canopy, and the more even the crop.
DLI at your photoperiod: PPFD × hours × 0.0036, so 900 µmol/m²/s on 12/12 is about 38.9 mol/m²/day. See PPFD and DLI for Cannabis.
Power and circuits: total watts, current at your voltage and how many fixtures go on each circuit.
Rebate check: whether the model is DLC listed, meets your utility's µmol/J floor, and what the application needs. See Grow Light Rebates in 2026.
Mistakes a plan catches
Hot centre, dim edges. Rooms laid out by dividing square footage by fixture coverage often hit the target in the middle and miss it along the walls, where many plants sit.
Overbuying. If the model shows you hit your target with fewer fixtures at a lower hang height, you save on fixtures, power and HVAC.
Wrong voltage. Buildings that run 208V, 240V, 277V or 480V need fixtures and circuits that match. Discovering this on install day is costly.
A layout that blocks work. Fixtures have to clear irrigation lines, trellis and the path a cart takes down the aisle.
A lost rebate. Some programs require a lighting design for pre-approval, and some set an efficacy floor above the DLC minimum.
Under canopy lighting needs planning too
If you're adding under canopy bars, the plan should treat them as a second layer: bars per bed, placement along each row, how they share circuits, and how they're grouped on the controller so they can ramp separately from the top lights. A Master Controller drives up to 100 AG-140 bars directly, or up to 1,000 per group using the bar's built-in signal booster. For a quick estimate, see How Many Under-Canopy Light Bars for a 4×4 or 4×8 Bed?
What to send for a plan
The more of this you include, the faster and more accurate the plan:
Room dimensions (length, width, ceiling height) and a sketch or drawing if you have one.
Canopy area: bench or table sizes, number of tiers, aisle widths.
Mounting height available above the canopy, and any obstructions (ducts, beams, irrigation).
Crop and stage for each room: clone, veg, flower, or a mix.
Target PPFD or DLI, if you have one, and whether you add CO₂.
Available voltage and panel capacity, if known.
Current fixtures if this is a retrofit, for example 1000W HPS.
Your electric utility, so we can check rebates.
Photos of the room help as well.
Why ours is free
Our view is simple: a lighting plan should be engineered before you buy, not after. We model your room with our fixtures, send back the layout, PPFD map, power figures and rebate check, and you decide. There's no obligation, and the plan is yours to keep.
We've done this for flower rooms, under canopy retrofits and 1:1 HPS replacements. One of them is The Iron Lung in Las Cruces, New Mexico.
Grower's Choice has supplied commercial horticultural lighting for more than a decade from Southern California, with warranties backed by a company that is still here to answer the phone, and our fixtures are ETL certified and DLC listed.
Request your free light plan. Include your room size, crop and utility, and we'll take it from there.
Planning under canopy light as part of the room? See the AG-140 Under Canopy LED Kit or all under canopy lights.
FAQ
What is a photometric light plan for a grow room?
It's a computer model that places specific fixtures in your room at a set spacing and hang height and calculates the PPFD across the canopy, so you can check coverage, uniformity, DLI and power before you buy.
What is a good uniformity for a grow room?
Uniformity is usually reported as minimum PPFD divided by average PPFD. Higher is more even. Compare options on the same basis and look closely at edges and corners, where the minimum usually sits.
How long does a light plan take?
It depends on the room and how complete the information is. Sending dimensions, canopy layout, hang height, voltage and your utility up front speeds it up.
Do I need a light plan for a rebate?
Some programs require a lighting design or a before-and-after comparison for pre-approval; others need only spec sheets and a DLC listing. A plan covers both.
Is the Grower's Choice light plan really free?
Yes. There's no charge and no obligation to buy.
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