LED Grow Lights for Home Gardeners: How Much Light You Need and Which to Buy

The right grow light depends less on the brand and more on what you're growing. Seedlings on a shelf need a modest amount of light for a few weeks. Lettuce and herbs need more. Tomatoes and peppers that you want to flower and fruit indoors need a lot more, and that's where cheap lights fall short. This guide covers how much light each needs, how to read the numbers on a spec sheet, and three brands listed on GardenTech that cover those jobs.

How much light do plants actually need?

Growers measure light for plants as the daily light integral (DLI): the total amount of usable light a plant gets in a day, in moles per square meter per day. It's the most useful single number because it combines how bright the light is with how many hours it's on.

Michigan State also notes that head lettuce is prone to tip burn once light climbs to around 16–17, depending on the variety and airflow, so more isn't always better for greens.

Turning a spec sheet into daily light

Grow light makers publish PPFD charts: how much light lands on the plants at a given height, in µmol per square meter per second. To turn that into a daily total, multiply PPFD × hours the light is on × 0.0036. For example, a light giving 200 PPFD at canopy height for 16 hours delivers 200 × 16 × 0.0036 ≈ 11.5 a day, right in the range for most seedlings. Tomatoes grown to fruit would need roughly twice that or more.

Hours and height for seedlings

Iowa State University Extension recommends running seedling lights on a timer for 14–16 hours a day, with fluorescent tubes about 4–6 inches above the seedlings and LEDs about 8–12 inches above, raising the lights as the plants grow. For larger LED boards, follow the hanging height in the maker's PPFD chart.

How to read a grow light spec sheet

• Actual watts, not "equivalent" watts. This is the power the light really draws, which sets your electricity cost and roughly how much light you get. Be wary of listings that lead with a big "1000W equivalent" number.
• PPF (µmol/s). The total amount of light for plants the fixture puts out. More PPF covers a bigger area or gives more light to the same area.
• Efficacy (µmol/J). How much plant light you get for each watt of electricity. Higher is better: a 2.7 µmol/J light gives about 35% more light per dollar of electricity than a 2.0 µmol/J light.
• Coverage. Makers often give a larger footprint for leafy growth and a smaller one for flowering and fruiting plants, which need more light. Use the smaller number for tomatoes and peppers.
• Lumens and color temperature. Lumens measure light as people see it, not as plants use it. A 6400K (cool white) light is fine for seedlings and greens, but lumens alone won't tell you whether a light can fruit tomatoes.
• Dimming, warranty and voltage. A dimmer lets one light work for seedlings and mature plants. Look for a multi-year warranty, and check the light matches your outlet voltage.

The three brands compared

SunBlaster: made for seed-starting shelves

SunBlaster's strip lights are long, slim fixtures that link end to end, so you can run several over a shelf of seed trays from one outlet. Their LED strips are 6400K, rated for 50,000 hours, and the company says they're interchangeable with its older T5HO fluorescent kits. The NanoDome kit pairs a 10×20 inch tray and tall humidity dome with a strip light and reflector, which is a tidy setup for seedlings, cuttings and herbs. SunBlaster sells through garden centers and online retailers rather than direct.

MARS HYDRO: lower-cost boards for small spaces

MARS HYDRO's TS series are square LED boards that hang over a shelf or a small grow tent. The TS 600 (100W, 2.0 µmol/J) covers about 2×2 ft for leafy growth, and the TS 1000 (150W, 2.3 µmol/J) about 2.5×2.5 ft. Both are dimmable and carry a 5-year warranty. They're less efficient than Spider Farmer's boards, so they cost a little more to run for the same light, but they're a good-value step up from strip lights for herbs, greens and strong seedlings. The TS 600 page notes it needs a 110–120V outlet.

Spider Farmer: more light per watt for fruiting plants

Spider Farmer's SF series are the most efficient boards in this guide. The SF2000 draws 200W at 2.7 µmol/J and covers about 2×4 ft, which is enough for tomatoes or peppers in a small grow tent. The smaller SF1000 (100W, 2.5 µmol/J) suits a 2×2 ft space. They're dimmable and carry a 5-year warranty, and the newer SF2000Pro uses Samsung LM301H EVO diodes rated for 55,000 hours. Higher efficiency means lower running costs if you run lights 12–16 hours a day all winter.

What it costs to run

Multiply actual watts × hours a day ÷ 1,000 to get kilowatt-hours, then multiply by your electricity rate (it's on your bill). For example, a 200W light on for 16 hours uses 3.2 kWh a day; at 15 cents per kWh that's about 48 cents a day, or roughly $14.50 a month. A 32W strip light on the same schedule uses about 0.5 kWh, around 8 cents a day.