LED vs CMH vs HPS: which grow light actually makes sense in 2026

HPS (high pressure sodium) is the old standard: a bulb plus a separate ballast, heavy on red/orange spectrum, cheap to buy, expensive to run, and hot. A 600W HPS fixture runs $80 to $150 and the bulb needs replacing every 10 to 14 months of regular use as output degrades.

CMH (ceramic metal halide, sometimes sold as LEC) uses a single-ended bulb with a fuller spectrum closer to daylight, including some UV-A. A 315W CMH fixture is the common home-grow size, runs $150 to $250, and the bulb typically lasts 10,000 to 20,000 hours, roughly one to two grow seasons of daily use.

LED quantum boards (built around diodes like Samsung's LM301 series) are the current standard for new builds. Full spectrum, cool-running relative to the other two, higher upfront cost, and diodes rated for 50,000+ hours, which in practice means the fixture outlasts several grow cycles without meaningful output loss.

Grow lights are compared on μmol/J, how much usable light (PPFD) a fixture produces per watt of electricity. Older HPS fixtures run around 1.5 to 1.7 μmol/J. CMH is a step up at roughly 1.7 to 1.9 μmol/J. Quality LED quantum boards from brands like Spider Farmer, Mars Hydro, or HLG commonly hit 2.5 to 2.9 μmol/J, meaning the same light output for noticeably less electricity draw.

Over a full grow cycle that gap adds up. A 4x4 tent under LED pulling 480 to 600W actual draw for 12 hours a day in flower costs meaningfully less over a season than a 600W HPS fixture producing comparable light, before even counting the HPS bulb replacement.

HPS runs hottest by a wide margin. A 600W HPS fixture can push tent temperatures up 10 to 15°F above ambient room temperature, which usually means adding AC or a bigger exhaust fan just to keep pace, especially in summer. CMH runs hot but noticeably less than HPS. LED runs coolest, often only a few degrees above ambient at typical hang heights, which is part of why LED lets growers run tents closer to the canopy without scorching leaves.

That heat difference is a real cost most first-time budgets miss. A grower who upgrades from HPS to LED frequently finds they can downsize their exhaust fan or drop a portable AC unit entirely, which offsets some of LED's higher sticker price.

HPS is red/orange-heavy, historically favored for flower because that part of the spectrum drives bud development well. It's weak in blue light, which matters more in veg. CMH and full-spectrum LED both cover the range more evenly, including blue wavelengths that support tighter internodal spacing and, in CMH's case, some UV-A that some growers report increases trichome density, though the evidence for that specific claim is thinner than the marketing suggests.

In practice, a full-spectrum LED run correctly (right height, right intensity) performs at least as well as HPS for flower, and most new commercial builds have already made the switch. Spectrum differences show up more in things like leaf color and grower comfort under the light than in a measurable yield gap between a well-run LED and a well-run HPS.

A 4x4 LED quantum board runs $250 to $450. A comparable HPS setup runs $100 to $180 but needs a new bulb roughly once a year at $30 to $50 each, plus higher electricity draw for the same coverage, plus likely a bigger exhaust or AC investment for the extra heat. Run the math over three years rather than the first purchase and LED is usually the cheaper option overall, not just the greener one.

CMH lands in between: bulb replacement cost is real but less frequent than HPS, and running cost sits closer to LED than to HPS. It's a reasonable pick for a single small tent where the higher LED entry price doesn't make sense yet.