For twenty years the serious indoor light was a high-intensity discharge lamp — an orange HPS for flowering, a blue metal halide for veg. They still work, they're still cheap, and forums are still full of people who swear by them. But the question in 2026 isn't whether LEDs can replace them; it's whether there's any case left for HID at all. Mostly there isn't. Here's the honest comparison, including the exceptions.
What the two actually are
HID (high-intensity discharge) lamps make light by arcing electricity through a gas inside a bulb. The three kinds you'll meet:
- HPS (high-pressure sodium) — orange-yellow light, the classic flowering lamp. 400, 600 and 1000 W.
- MH (metal halide) — bluer light, used for vegetative growth. Same wattages.
- CMH / LEC (ceramic metal halide) — a newer, fuller-spectrum HID, usually 315 W, that does both stages tolerably.
All need a separate ballast to run, a reflector hood to point the light down, and a bulb that fades and needs replacing.
LED grow lights are panels or bars of diodes driven by a built-in power supply. Modern ones are "full-spectrum white" — mostly white diodes with a few deep reds — and are dimmable. Older "blurple" panels (pink-purple light from separate red and blue diodes) are also LEDs but a generation behind.
The comparison
| HPS / MH | CMH | Modern white LED | |
|---|---|---|---|
| Efficacy (light per watt) | ~1.7 µmol/J | ~1.9 µmol/J | 2.5–3.0+ µmol/J |
| Heat into the tent | Very high, radiant | High | Lower, mostly convective |
| Hanging distance | 18–30 in | 18–24 in | 12–24 in |
| Spectrum | Narrow (orange or blue) | Fairly full | Full, tunable |
| Dimming | Only with a dimmable ballast, in steps | Limited | Continuous, 0–100% |
| Bulb life | 6–12 months of use, fading throughout | ~2 years | 50,000 hours (years of daily use) |
| Upfront cost, 4×4 tent | $100–200 (600 W kit) | $250–350 | $300–600 (450 W class) |
| Running cost | Highest — bulb plus extra ventilation | High | Lowest |
| Noise | Ballast hum, often a fan | Ballast hum | Silent (passive) |
The efficacy row is the whole story. A modern LED turns electricity into usable light at roughly 1.5× the rate of HPS. So a 450 W LED produces about what a 600 W HPS does — while also not needing a ballast (another 50–70 W), not dumping radiant heat onto the canopy, and not needing a bulb every season.
The heat question, properly
Every watt drawn eventually becomes heat in the room — that's physics, and it's true of LEDs too. The difference is how it arrives. An HPS bulb runs at several hundred degrees and radiates heat straight down onto the leaves, which is why it has to hang two feet up and why tents with HPS need roughly a third more exhaust. An LED's heat comes off its heatsink into the air, where the fan removes it, and the leaves under it aren't being cooked from above. Same watts, very different experience — and since the LED draws fewer watts for the same light, less heat in total.
For fan sizing with either, see Sizing a grow tent fan.
What "600 W HPS equivalent" means on an LED box
Nothing precise. It's a claim that the LED gives roughly the light of a 600 W HPS — sometimes true, often not, and unverifiable from the box. Use the LED's actual power draw and its PPFD map instead; What LED wattage really means explains how to read them. As a rule of thumb, a good 450–500 W LED does replace a 600 W HPS in a 4×4, and a 250 W LED replaces a 400 W HPS in a 3×3 or 2×4.
Where HID still makes sense
There are a few, and they're worth being honest about:
- A cold space. A garage or basement in winter may need the heat an HPS throws off. An LED there means adding a heater.
- The tightest possible budget. A used 600 W HPS kit for $80 grows plants. The LED that replaces it is four times the price. You'll pay the difference back in electricity and bulbs within a year or two — but if the money isn't there now, HID works.
- Very large spaces where fixture count and price per square foot dominate, and heat is managed by a proper HVAC system anyway.
- You already own one. A working HPS is worth running until it makes sense to replace, not throwing away because LEDs exist.
For a tent in a house — a bedroom, a closet, a spare room — none of those apply, and the case for HID is gone.
The switch, if you're making it
Coming from HPS to LED, three things catch people out:
- Hang it closer. LEDs sit 12–18 inches above the canopy, not 24–30. Too high and you lose light to the walls.
- Feed a little less nitrogen, and watch calcium and magnesium. Plants under LED run cooler and transpire less, so they take up less; cal-mag deficiency after switching is common enough to plan for.
- Expect less stretch. HPS's red-heavy spectrum makes plants stretch; under a white LED they stay shorter and bushier. Tents that were tight under HPS become comfortable.
Straight answer
For a tent in a home, buy a modern full-spectrum LED sized to the tent — the numbers are in Which LED for your tent. It costs more once, costs less every month, runs quieter and cooler, and never needs a bulb. HID keeps a place in cold rooms and on very tight budgets, and nowhere else.
As an Amazon Associate we earn from qualifying purchases made through links in this guide — at no extra cost to you. Picks are ours; prices and stock are Amazon's.