Best Grow Lights for Cannabis: LED vs HPS vs CMH (Ask Alex, 2026)

By James Buddsey · Updated October 30, 2026

For most home growers in 2026, a quality full-spectrum LED fixture is the best grow light for cannabis: it turns more electricity into usable light than HPS or ceramic metal halide (CMH), runs cooler and lasts longer. HPS still grows excellent buds at a lower purchase price, and CMH sits in between. Whatever you buy, judge it by photon output and efficiency (µmol/s and µmol/J) and by a PPFD map for your space, not by watts or lumens.

This article began as the first “Ask Alex” reader question, “Which light do I use to grow my cannabis?”, answered by our grow columnist Alex. Lighting has changed so much since then that we have rewritten it as a complete guide, keeping Alex’s core advice: match the light to your space, your ventilation and your plant height, and ignore marketing numbers that measure the wrong thing.

Grow Lights Compared at a Glance

Efficiency figures below come from independent measurements at Utah State University’s Crop Physiology Laboratory. Higher µmol/J means more plant-usable light per unit of electricity.

Sources: the HPS, CMH and fluorescent numbers are from a 2014 PLOS One comparison of fixtures by Nelson and Bugbee. The LED range and DLC minimum are from a 2020 review in Horticulture Research by Kusuma, Pattison and Bugbee, which reported that the best LED fixtures had climbed from 1.7 µmol/J in 2014 to 2.5 to 3 µmol/J.

The Numbers That Actually Matter

Alex’s biggest point still stands: lumens are the wrong measurement for plants. Lumens weight light by how bright it looks to the human eye, which peaks in green-yellow. Plants respond to photons across roughly 400 to 700 nanometers, called PAR (photosynthetically active radiation). Use these instead:

• PPF (µmol/s): total plant-usable photons a fixture emits each second.
• Efficacy (µmol/J): PPF divided by watts drawn from the wall. This is the fixture’s fuel economy.
• PPFD (µmol/m²/s): how many photons land on each square meter of canopy per second. This is what your plants feel, and it falls off as you raise the light.
• DLI (mol/m²/day): the day’s total light. DLI = PPFD × hours of light × 0.0036. For example, 600 µmol/m²/s for 12 hours is about 26 mol/m²/day.

A reputable maker publishes PPF, efficacy and a PPFD map showing readings across the footprint at a given hanging height. If a listing offers only “equivalent watts” or lumens, keep shopping. The DesignLights Consortium (DLC) keeps a list of horticultural fixtures that meet a minimum efficacy and safety requirements, a useful screen.

How Much Light Does Cannabis Need?

More than most houseplants. In a 2021 University of Guelph study, cannabis grown under LEDs during a 12-week flowering phase produced dry flower yields that rose in a straight line as canopy PPFD increased from 120 up to 1,800 µmol/m²/s. Bud density rose too, but light level had no effect on cannabinoid potency. That was one controlled indoor study; it shows cannabis can use very high light, not that a home tent should run at 1,800.

Very high intensity also needs everything else to keep up: CO2, temperature, water and nutrients. An earlier meta-analysis cited in our beginner’s growing guide found that more light raised output per square meter but lowered yield per watt. Many home growers use rough targets like these (grower rules of thumb, not research thresholds):

Raise intensity gradually and watch the plants. Bleached or yellowing top leaves and upward-cupping leaves are common signs the light is too strong or too close. Autoflowering strains do not need the switch to 12 hours; growers often keep them on long days throughout.

LED: The Default Choice

Modern LED fixtures are usually bar-style boards using white LEDs supplemented with deep red. They spread light evenly, produce little heat directly at the canopy, and can hang closer to the plants. The review by Kusuma and colleagues calculated that current LED technology could reach about 3.4 µmol/J for white-plus-red fixtures, so efficiency is still improving.

Alex took on three LED myths that still circulate:

• “LEDs don’t penetrate.” A dim-looking lower canopy under LED often reflects how the light looks to us, not how many photons reach the leaves. What matters is PPFD at different heights, which a PPFD map or a quantum meter shows.
• “More colors means a better light.” Not necessarily. A well-designed fixture with a few efficient diode types can outperform one stuffed with a dozen wavelengths.
• “Higher lumens means better.” Lumens favor green-yellow light and say little about plant growth. Compare µmol figures instead.

The trade-off is upfront cost. In 2014, Nelson and Bugbee found LED fixtures cost five to ten times more than HPS per photon delivered. Prices have dropped a great deal since, but a good LED still costs more than a basic HPS kit.

HPS and Metal Halide: Still Capable

High-pressure sodium lamps grew most indoor cannabis for decades, and a double-ended HPS fixture is still efficient. Their downside is heat: they put out a lot of radiant heat, so they need height, distance from the canopy and serious ventilation. Bulbs also lose output with age and need periodic replacement.

Alex favored metal halide over HPS for its broader spectrum, and he predicted ceramic metal halide (CMH, also called LEC) would become the top HID lamp. CMH did become popular, with good color and decent efficiency, but LEDs overtook it on efficiency.

Fluorescent and Incandescent Bulbs

T5 high-output fluorescent tubes are cheap, cool and gentle, which makes them good for clones and seedlings, but they are too weak and inefficient for flowering a full canopy.

A later Ask Alex column asked whether incandescent bulbs could grow cannabis. Alex disagreed with growers who dismiss them entirely, but he recommended them only as a supplement: a few low-wattage bulbs (10 to 25 watts) adding red and far-red light to an LED or fluorescent setup, never as the main light. Today that role is better filled by far-red LED bars. Incandescent bulbs turn most of their power into heat rather than useful light, and they are a burn risk close to leaves.

How to Choose: Match the Light to Your Space

1. Measure the footprint. Buy a fixture rated to cover your tent or area, with a published PPFD map for that size.
2. Check your height. Low ceilings and small tents favor LED. HID lamps need more clearance.
3. Plan for heat and air. Every watt ends up as heat in the room. Size your exhaust fan accordingly, especially with HPS.
4. Compare efficacy and warranty. A higher µmol/J pays back in electricity over years of use.
5. Use a timer and dimmer. A dimmable driver lets one light serve seedlings and flowering plants.

Electrical safety: plug lights into a properly rated outlet and timer, avoid daisy-chained power strips, keep water away from cords, and never cover or disable a smoke detector in a grow space. Tampering with detectors is dangerous and often illegal for renters. Control smell with ventilation and a carbon filter instead; see our odor guide.

Where Home Growing Is Legal

Adults 21 and older in Oregon may grow up to 4 plants per household. In Washington, only registered medical patients may grow at home. See our Oregon and Washington law guides. Starting from seed? Read how to germinate cannabis seeds and our list of top strains to grow indoors.

Grow Lights for Cannabis FAQ

More grow guides are in Cannabis 101.

For adults 21+ in legal states. General information, not medical advice.