Best Grow Lights for Container Gardens: How to Choose

The Short Answer

For most indoor container gardens the best grow light is a white LED bar or panel that you can raise and lower, hung 12 to 24 inches above the foliage and run on a timer for 12 to 14 hours a day. Size it by the light the crop needs, measured as daily light integral (DLI). Lettuce needs a DLI of 12 to 17 and a tomato needs 20 to 30, so a fixture that grows fine salad greens can leave a fruiting plant short.

The rest of this guide explains how to set that target, how the lamp types compare, and how to hang and time the fixture.

Set a Light Target for the Crop

Plants use photosynthetically active radiation, or PAR, which Purdue Extension defines as light with a wavelength between 400 and 700 nanometers. Two measurements describe it. PPFD is the intensity landing on the leaves at one moment, in micromoles per square meter per second. DLI is the total for the day, in moles per square meter per day. PPFD is the speed and DLI is the distance covered.

Virginia Cooperative Extension publishes suggested DLI ranges for common crops:

Crop	Suggested DLI (mol per square meter per day)
Seedlings	5 to 10
Micro-greens	9 to 12
Parsley	10 to 15
Lettuce	12 to 17
Spinach	14 to 20
Cilantro	15 to 20
Basil	15 to 25
Tomato, cucumber	20 to 30

Iowa State University Extension groups plants in a similar way. Its low-light category of 3 to 6 covers foliage houseplants, the high-light category of 12 to 16 covers herbs, leaf vegetables and seedlings, and the very-high category of 18 to 30 covers herbs, fruits and vegetables. Foliage plants at the low end are a different buying problem, covered in the guide to grow lights for low-light apartments.

To check a fixture against the target, multiply its PPFD by the hours it runs and then by 0.0036. A light that holds 250 PPFD across the shelf for 14 hours gives a DLI of 12.6, enough for lettuce and parsley. At 400 PPFD for the same 14 hours the result is about 20.2, which reaches the bottom of the tomato range. Virginia’s own worked example is 200 PPFD for 16 hours, which comes to 11.5.

Read PPFD, Not Equivalent Watts

A wattage figure on the box tells you what the fixture draws from the wall. It does not tell you how much light reaches the plant. Look for a PPFD figure quoted at a stated distance, and pass over listings that give only an “equivalent” wattage.

You can also measure what you have. Iowa State describes placing a light meter or a smartphone app at foliage level, reading lux or footcandles, and multiplying by the conversion factor the manufacturer supplies for that lamp to get PPFD. One footcandle equals 10.764 lux. Virginia Cooperative Extension notes that phone apps are typically the most cost-effective option, while standalone quantum sensors run from under $100 to more than $1,000.

Measure at the height of the leaves, since that is where the number counts. Because DLI is a total for the whole day, light from a sunny window counts toward it and the fixture only has to make up the rest.

Compare the Main Types

Iowa State University Extension’s guidance covers four lamp types that home growers meet.

Type	Distance from foliage	Strengths	Limits
LED	12 to 24 inches	Efficient; less heat than fluorescent; long-lasting; output does not fade	Red and blue models cast a pink or purple light
Fluorescent (T5)	6 to 12 inches	T5 tubes are the most efficient fluorescent size	Intensity drops sharply; replace tubes every one to two years
Incandescent	Not advised	None for plants	Not a good source of supplemental light
HID	Farther than other types	Much higher output than other fixtures	Large, hot and costly; common in commercial greenhouses, less so in homes

LED is the practical choice for a shelf of containers. Older T8 and T12 fluorescent tubes are being phased out, so a new fluorescent setup should use T5 tubes if you go that way.

Color deserves a note. Plants primarily use red and blue wavelengths, which is why some LED fixtures emit only those and glow pink or purple. Blue light helps control excessive stem elongation. Red light drives photosynthesis and promotes flowering and fruiting, and it also causes stretching. A white LED includes both and has the practical advantage that leaves look their true color under it, so yellowing or pest damage is easy to see. On a Kelvin rating, lower numbers are redder and higher numbers are bluer.

Hanging Height and Coverage

Start an LED fixture 12 to 24 inches above the foliage and a fluorescent fixture 6 to 12 inches above it. Those are Iowa State’s ranges for most cases, and the plants will tell you which end to use.

Signs of too little light are excessive stretching, spindly growth, yellowing foliage, leaf drop and absent flowers. Lower the fixture, raise its output or add hours. Signs of too much are leaf scorch, bleached leaves, excessive reddening and extremely compact growth. Raise the fixture or dim it.

Plants grow toward the lamp, so the gap closes over the season. Hang the fixture on an adjustable chain or set pots on something you can remove later. A reflector that directs light downward lets plants use more of what the fixture emits. Kitchen herbs are the most common crop on a lit shelf, and the guide to grow lights for herbs indoors in winter covers that setup.

Hours, Timers and Running Cost

For most species, 12 to 14 hours of light is a good length. Iowa State’s limits for home gardeners are as little as 10 hours and no more than 16 hours a day, which leaves at least 8 hours of darkness. A plug-in timer keeps the schedule steady.

Hours and intensity trade against each other within those limits. If the DLI math comes up short at 12 hours, extending to 16 hours raises the total by a third without a new fixture. Past 16 hours the answer is more PPFD: a closer or stronger light.

Running cost is plain arithmetic. A 60-watt fixture on for 14 hours uses 0.84 kilowatt-hours a day, or about 25 a month. Multiply that by the rate on your utility bill.

Grow lights also carry seedlings before the outdoor season. Seedlings need a DLI of only 5 to 10, so the same fixture can serve them. The page on grow lights for seed starting covers seedling distances and hours, and the guide to when to start seeds indoors covers the timing.