Tomato Grow Lights Explained

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Tomato grow lights (or plant grow lights) allow you to start seedlings and grow tomatoes indoors, even during the off season or when temperatures are cold outside.

Grow lights provide an electrical equivalent to sunlight.

Surprise … plants need darkness as well as light in order to grow best! You can pair your lights with a timer for convenience. 

An automatic timer helps make sure lights switch on and off each day so that seedlings and plants are in the dark each day.

Here’s the dirt on how tomato grow lights work and what options you can choose from.

4 parts of a tomato grow light with Tomato Dirt

The anatomy of a grow light

Tomato grow lights systems have 4 main parts:

  • Stand: the structure from which lights are suspended and under which plants are set
  • Electrical ballast: the electrical component, connected to a cord, that controls the light current
  • Lamp: the type of bulb that gives off light
  • Reflector: a shield that maximizes the light received by plants and controls heat produced by lamps

“It sounds complicated with all those parts …”

It’s not.

Many systems for the home gardener provide the ballast, lamp, and reflector together as a package. (You can also purchase replacement lamps). You simply need to make a couple of decisions: what type of lamp will best meet your needs and what kind of stand (structure) works for you.

In choosing a tomato grow light system, consider two questions

  1. What type lamp will be best for what you want to grow?
    Determine your goals: will you start seeds indoors? Grow plants indoors? Grow plants in a greenhouse? (Find greenhouse plans here.) The type of indoor tomato gardening you want to do will guide which type of tomato grow lights you select
  2. What type of stand (structure) will be best for your situation?
    Decide how much room you want to dedicate to your tomato grow lights system. Assess and measure your dedicated growing area in order to choose the grow light stand or structure that will work best for you. View different grow light systems you can choose from.

Which type of lamp should I choose?

This is the area that can be most confusing for indoor gardeners. But never fear – here’s a short summary to help you understand tomato grow lights and make a good decision.

Understand “color temperature”

Different grow lamp types emit light in different ways.

The light spectrum in grow lights is expressed in degrees Kelvin (K), a number that indicates a visual “temperature.”

Grow lights with higher color temperatures (5000-6500K) provide the full light spectrum and promote all stages of vegetative growth. They emit light with a bluish tinge. Grow lights with lower color temperatures (2500-3000K) are known to encourage flowering and are often used when the plant develops fruit. They put off a reddish or even yellow glow.

The best artificial light source for tomatoes imitates the light in their natural environment. Natural daylight has a high color temperature (about 6000 K). Select your grow lights accordingly.

Understand your lamp options

There are four kinds of plant grow light lamps to choose from.

Each emits light differently. Read on …

1. Incandescent plant grow lights

Though not technically a grow light, incandescents are often labeled and used as one. They convert much of their electricity into heat rather than light, making them fairly inefficient as grow lights, particularly for indoor vegetable crops like tomatoes.


Use: secondary or supplemental lighting for individual house plants
Color temperature: low (about 2700K)
Average life span: 750 hours

2. Fluorescent plant grow lights

Fluorescent plant grow lights are one of the most popular options for the home gardener or hobbyist. They’re available in at least 3 options: Standard T12 fluorescents, High Output (HO) T5 fluorescents, and compact fluorescents (CFL).

Standard T12 fluorescents

Use: best for starting seedlings and growing low-light plants
Color temperature: up to full spectrum (5000K)
Average life span: up to 20,000 hours

High Output (HO) T5 fluorescents

Use: primary light source for indoor growing; excellent for all growing applications including starting seeds, propagating cuttings, growing leafy vegetation, and flowering. Produce twice as much light as standard fluorescent lamps.
Color temperature: available in low (2700K) and high (6500K)
Average life span: 10,000 hours

Compact fluorescents (CFL)

Use: propagation and larger plants. Compacts are a smaller version of High Output (HO) fluorescents but have specially-designed reflectors to focus direct light to plants.
Color temperature: available in low (2700K), full spectrum (5000K) and high (6500K)
Average life span: 10,000 hours

More on fluorescent grow lights ...

3. HID (High Intensity Discharge) plant grow lights

HIDs are the plant grow lights of choice among professional horticulturalists and large-scale indoor growers – those who produce the thousands of tomato plants that you see for sale in nurseries and home improvement centers each year.

HID plant grow lights come in two types: Metal Halide (MH) and High Pressure Sodium (HPS). Each has its advantages. Metal halide lamps provide a full spectrum of light and are used for all stages of vegetative growth. High pressure sodium lamps are used when plants flower and develop fruit or as a supplemental light source.

In addition, growers can install grow lights that combine MH and HPS lamps: combination lamps (burn both MH and HPS in the same reflector) or switchable lamps (burn both in the same fixture, not at the same time).

Metal Halide (MH) lamps

Use: primary light source if little natural light is available
Color temperature: full spectrum
Average life span: 10,000 hours

High Pressure Sodium (HPS) lamps

Use: secondary or supplemental lighting for natural lighting, especially in greenhouses. HPS lamps are helpful when plants flower and develop fruit.
Color temperature: low (2200K)
Average life span: 18,000-20,000 hours

4. LED plant grow lights

The newest lamps among plant grow light technology, LED grow lights are developing a reputation for economy and efficiency. They consume less power and produce less heat than other lamp types.

Use: primary lighting or as supplementary lighting to HIDs
Color temperature: LEDs emit wavelengths corresponding to chlorophyll’s production peaks
Average life span: up to 50,000 hours

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