For most indoor gardens, LED grow lights are the better choice today: a good LED fixture delivers the same plant light as an HID lamp for noticeably less electricity and puts less heat on the plants. HID lights still work, but you give up efficiency, control and convenience.
What are HID grow lights?
HID stands for high-intensity discharge. An HID grow light passes electricity through a gas inside a glass bulb to make light, and it needs a separate ballast to regulate the current. Two types dominate indoor growing:
- Metal Halide (MH) lamps give off a bluer light, so growers use them for the vegetative stage, when plants build leaves and stems.
- High-Pressure Sodium (HPS) lamps give off a yellow-orange and red light, so growers use them for flowering and fruiting.
That split is the reason HID growers own two kinds of lamp and swap one for the other partway through a crop.
How LED grow lights work
An LED grow light uses many small diodes mounted on a board and cooled by a heat sink. A driver converts household power to the low-voltage current the diodes need. Because the diodes can be mixed and dimmed, one fixture can supply a full spectrum for every stage of growth, with no bulbs to replace and no separate ballast.
Efficiency: how much plant light per watt?
The fair way to compare lights is photon efficacy, written as µmol/J: micromoles of plant-usable light produced per joule of electricity. Researchers at Michigan State University and Utah State University have measured this for both lamp types:
- A 400-watt single-ended HPS lamp with a magnetic ballast produces about 0.9 µmol/J.
- A 1,000-watt double-ended HPS lamp with an electronic ballast produces about 1.7 µmol/J.
- Many newer LED fixtures exceed 2.0 µmol/J. One commercial LED system tested at Utah State and Rutgers measured about 2.05 µmol/J.
The same researchers also found that LEDs are not all equal. In earlier testing the LED fixtures on the market ranged from about 0.89 to 1.70 µmol/J, so some were no better than a good HPS lamp. The lesson is to compare measured efficacy, not the word LED. The diodes matter too: a Samsung LM301H EVO chip is rated at 3.14 µmol/J on its own, but a finished fixture always delivers less than its bare chip, because drivers, optics and heat cost a little efficiency.
| Feature | HID (MH and HPS) | LED |
|---|---|---|
| Efficacy | About 0.9 to 1.7 µmol/J for HPS | Many fixtures above 2.0 µmol/J |
| Spectrum | MH is bluer, HPS is yellow-orange and red | Full spectrum available from one fixture |
| Heat | Radiates heat toward the plants | Carries heat away from the plant side |
| Warm-up | Needs time to warm up and to cool down | Full output straight away |
| Dimming | Limited, depends on ballast | Built-in dimming is common |
| Parts | Bulbs and a ballast | Driver and diodes in one fixture |
Heat and cooling
Every light turns some of its electricity into heat. What differs is where the heat goes. Research summarized by Michigan State University notes that LED fixtures dissipate much of their heat away from the surface they illuminate, while HPS fixtures send more heat toward the plants. That is why a plant canopy can usually sit closer to an LED fixture without scorching.
An LED does not remove the need for ventilation. A grow tent still needs fresh air, and a room full of lights still warms up. There is also a trade-off in cold places: in a computer model of a greenhouse, switching to LED saved lighting electricity but required extra boiler heat, so part of the saving came back as heating cost. In a warm indoor room or a tent, the lower power draw usually means less heat to remove.
Spectrum and growth stages
Traditional growers match the lamp to the stage: MH for vegging and HPS for flowering. A full-spectrum LED covers both with one fixture, and a dimmer lets you lower the intensity for seedlings and raise it for fruiting. Our guide to which growth stages your LED lights can be used at explains how to run one light from seedling to harvest, and full spectrum LED grow lights explains what the spectrum contains.
Running cost: a worked example
Electricity is billed by the kilowatt-hour (kWh): one kilowatt of power used for one hour. The U.S. Energy Information Administration expects U.S. households to pay about 18.2 cents per kWh in 2026, so we will use that, and 12 hours of light a day for 30 days (360 hours).
- HID light: a 1000w HID actually draws closer to 1100w. 1.1 kW × 360 hours = 396 kWh, which costs about $72 a month.
- LED light using roughly half the power: about 550w. 0.55 kW × 360 hours = 198 kWh, which costs about $36 a month.
That is about $36 saved per light per month at those assumptions, before counting any saving on cooling. Your rate and hours will differ, so use the same arithmetic with your own bill.
When HID still makes sense
HID is not obsolete for everyone. If you already own working HID equipment and your growing space is cold, the extra heat can be useful. HID fixtures also cost less to buy for the same wattage. But if you pay for the electricity and the cooling, or you want one light for every stage, LED is the sensible upgrade.
How to choose
- Pick LED if you want lower running cost, less heat on your plants and one light for every stage.
- Compare efficacy in µmol/J from independent or manufacturer test data, not wattage or marketing claims.
- Check that the diodes are genuine and named. Read about Samsung LM301B LED grow lights.
- Work out the lights you need for your space with our guide to how many LED grow lights you need.
Common myths about LED and HID grow lights
- "LEDs run cold." They do not. An LED turns a large share of its electricity into heat. The difference is that the heat leaves from the back of the fixture, through the heat sink, instead of radiating onto the plants.
- "All LEDs are the same." Efficacy, spectrum, drivers and build quality vary widely. A cheap fixture can be less efficient than a good HPS lamp.
- "HID penetrates the canopy better." An LED spreads its light across a wide board, which can light lower leaves evenly, and a full spectrum includes the green light that travels deepest into a canopy.
- "You need different lights for flowering." That is an HID habit. A full-spectrum LED with a dimmer covers every stage.
Switching from HID to LED: what changes
Moving an existing garden to LED is straightforward, but a few habits change:
- Hang height. Because there is less radiant heat, you can often hang an LED closer than an HID lamp of similar output. Start high or dimmed and move down in small steps. See how far to hang LED grow lights from plants.
- Watering. Less heat on the plants and the growing medium means they may dry out more slowly. Check moisture before you water.
- Ventilation. You will probably need less cooling, but keep the fans for fresh air and humidity.
- Settings. Use the dimmer to match intensity to each stage instead of changing lamps.
- Eye protection. Full-spectrum LED light is much more comfortable than blurple, but UV eye protection is still recommended.
Key takeaways
- A good LED gives the same plant light as an HID lamp for noticeably less electricity, often well under half the power of an older lamp.
- Compare measured efficacy in µmol/J, not the word LED: some LED fixtures are no better than a good HPS lamp.
- LED heat leaves from the back of the fixture, so plants can sit closer, but a tent still needs fresh air.
- One full-spectrum LED with a dimmer replaces the MH and HPS pair.
- HID can still make sense where heat is useful and equipment is already paid for.
Where My LED grow lights fit
My LED Grow Lights use Samsung LM301b/h LEDs and use roughly half the power of traditional HID's. They give a full spectrum from one fixture and they carry a 3-year warranty as standard unless otherwise noted in the product description. See all of our LED grow lights.