120V, 208V, 240V, 277V or 480V? Choosing the Right Voltage for Commercial Grow Lights
The voltage you run your grow lights on decides how many fixtures fit on each circuit, how much wire and how many breakers the job needs, and which version of a fixture you order. It's also one of the easiest things to get wrong, because the answer depends on what your building already has, not on which voltage sounds best.
This guide covers what each voltage usually means in a commercial building, how to do the circuit math, and how to match fixtures to your service. Your electrician and local code have the final word, so use this to plan, not to wire.
Start with what your building supplies
Commercial buildings in the U.S. usually have one of these services:
120/240V single phase. Common in smaller buildings and converted spaces. Gives you 120V and 240V.
208Y/120V three phase. Very common in commercial buildings. Line to line is 208V, not 240V. This catches people out: a fixture sold as "240V" must also accept 208V if that's what your panel delivers.
480Y/277V three phase. Common in larger warehouses and industrial buildings. Line to neutral is 277V, the standard commercial lighting voltage, and line to line is 480V.
Find out which you have before you choose fixtures. Your electrician can tell you from the panel, or your utility can from the account.
Why higher voltage often costs less to wire
For the same power, current falls as voltage rises: amps ≈ watts ÷ volts for fixtures with a power factor close to 1. Lower current means more fixtures per circuit, fewer circuits and breakers, and less copper.
Take the AG-140 under canopy bar, which draws 140 W and accepts 120–277V:
Voltage | Approx. amps per bar | Bars per 20 A circuit at 16 A continuous |
120V | 1.17 A | 13 |
208V | 0.67 A | 23 |
240V | 0.58 A | 27 |
277V | 0.51 A | 31 |
Grow lights run for hours at a time, so they are usually treated as a continuous load. U.S. code sizes continuous loads at 125%, which in practice means loading a 20 A breaker to no more than 16 A. The table uses that 16 A figure. These are circuit limits only. How many AG-140 bars you can daisy-chain on one run is a separate limit that also depends on voltage; see How Many Under-Canopy Light Bars for a 4×4 or 4×8 Bed?
The same bars on 277V need well under half the circuits they would on 120V.
Matching fixtures to your service
Our fixtures come in input ranges built for these services:
AG-140 under canopy bar: 120–277V. One model covers 120V, 208V, 240V and 277V, so it fits almost any building. If you're starting small, the AG-140 Under Canopy LED Kit bundles bars with cords and stands; tell us your voltage when you order.
AG-250 HW: 240–480V, 750 µmol/s. Built for higher-voltage commercial services, including 480V.
ROI-F720: 2,354 µmol/s, sold in a 240V version ($356) and a 277V version ($376). Choose the one that matches your circuits. If your building is 208V, confirm the input range with us before you order.
TSL-800: designed as a 1:1 replacement for 1000W HPS, typically on the circuits the HPS already used. See TSL-800 vs 1000W HPS.
Retrofits: reuse what's there
If you're replacing HPS, you usually already have circuits at 208V, 240V or 277V feeding the old ballasts. An LED that accepts the same voltage can often reuse those circuits, and because the LED draws less power than the 1000W HPS it replaces, each circuit has headroom left over. Have your electrician confirm receptacles, breakers and wire before you plan to add load.
Choosing, in three questions
What does the panel give you? 120/240V, 208Y/120V or 480Y/277V.
How big is the room? The more fixtures, the more the savings from higher voltage add up, which is why larger facilities often choose 277V or 480V where the service allows.
Do you want one model for every room? A wide input range such as the AG-140's 120–277V keeps spare parts simple across rooms with different services.
Other things to check
Power quality. Some utilities require a minimum power factor and a maximum total harmonic distortion for rebates. LADWP, for example, requires PF of at least 0.9 and THD of 20% or less.
Control wiring. Plan the dimming control runs along with the power circuits. A Master Controller runs up to 100 bars directly, or up to 1,000 per group using the bars' built-in signal booster.
Certification. Our fixtures are ETL certified for electrical safety and DLC listed for efficacy, which most utility rebate programs require.
Not sure what your building has? Send a photo of the panel label with your room size, and we'll include the circuit plan in your free light plan.
Browse all under canopy lights.
FAQ
Is 277V better than 240V for grow lights?
Neither is better in itself. 277V draws a little less current for the same power, so more fixtures fit per circuit. The right choice is the voltage your building already supplies.
Can a 240V grow light run on 208V?
Only if its input range includes 208V. Many commercial buildings deliver 208V line to line, not 240V, so check the spec sheet or ask the manufacturer before ordering.
How many grow lights can I put on a 20 amp circuit?
Divide 16 A, which is 80% of the breaker for a continuous load, by the fixture's current. For a 140 W AG-140 bar that's about 13 at 120V and 31 at 277V. Fixture daisy-chain limits may be lower.
What voltage do commercial grow rooms use?
It depends on the building. Facilities with a 480Y/277V service often run lighting at 277V or 480V; many smaller commercial spaces have 208V or 240V.
Do I need an electrician?
Yes. Use a licensed electrician to confirm the service, size circuits and install to local code.
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