Tomatoes are the most popular home-grown crop in the world. However, they are only able to grow in a narrow temperature range. Growing tomatoes indoors solves that problem.
Why Use A Grow Light For Tomatoes?
Light from windows is seldom sufficient to grow good tomatoes, whether you are starting seeds or growing the whole plant indoors.
Starting Seeds
Poor light makes seedlings elongate and become weak. These seedlings are more likely to die when planted outdoors. In addition, seedlings will grow towards the light, whether that is overhead with a grow light or sideways toward a window. Using a grow light correctly will help you grow the hardiest seedlings each year.
Indoor Tomatoes
When it is too hot or cold to grow tomatoes outdoors, you can use a grow light to grow them indoors. Tomatoes can be grown indoors in a pot or hydroponically. However, tomato plants will not produce many tomatoes unless they get ample light. It is hard to provide this much light without using a grow light.
What Type Of Grow Light Is Best?
There are three types of lights used when growing tomatoes. Each has good points and bad points.
Fluorescent
Fluorescent lights use low-pressure mercury-vapor gas-discharge bulbs. An electric current in the gas energizes mercury vapor, which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow. Fluorescent lights are more energy efficient than incandescent light bulbs but are not as efficient as HID or LED bulbs. They are not much less expensive than LED lights. Fluorescent lights have a blue-white cast and typically do not have red light. Full spectrum fluorescent bulbs have all the light colors the sun does but cost more. In times past, people used fluorescent lights to add heat as well as light. However, they are not very efficient in heating a greenhouse. I do not recommend fluorescent lights anymore because LED lights are so much better.
High-Intensity Discharge (HID)
HID plant grow lights come in two types: Metal Halide (MH) and High-Pressure Sodium (HPS). They produce a very bright light when new, but when they get old, they lose 70% of their light. HID lights are usually used in commercial greenhouses and are not cost-effective for home use. I mention them only because you might come across the term.
Light-Emitting Diodes (LED)
LED lights last 2-5 times longer than fluorescent lights and use much less energy. They come in several colors or full spectrum lights. Many grow lights have both red and blue wavelengths where you can adjust the intensity of the light. LED lights produce very little heat, so won’t scorch your plants like fluorescent lights can. They cost a little more initially than fluorescent lights, but the energy savings and longevity are worth the extra money. LED lights come in bars or shaped like a light bulb. I use LED bars to light my plants.
Light Temperature
Plants use different temperatures of light during different stages of growth. A full-spectrum light will work for any tomato plant. However, if you are growing lots of tomato plants and want to harvest the most tomatoes, you will want to vary the temperature during different life stages. The temperature is expressed in degrees Kelvin (K). Here are the different light temperatures that are relevant to growing tomatoes.
- Blue/White light 5000K and above – Helps promote the germination of seeds and increase the growth rate of the plant.
- Warm White light 3000K – has more orange/yellow light and helps the plant to blossom.
- Red light 660 nm – Combines with blue/white light to increase the foliage and fruit.
- IR light 760 nm – infrared light helps the plant yield more.
If you are just starting seeds, a blue/white light is adequate. However, if you want to grow tomatoes indoors, you will need a light that contains red and blue light to get the best yield. Many LED grow lights contain both red and blue light with separate switches, so you choose what light the plants get at the various growth stages.
Light Intensity For Optimal Growth
LED lights can be very bright. Most have a dimmer switch to allow you to adjust the intensity of the light that shines on your plants. Here are the best settings for that dimmer switch by tomato growth stages.
- Germination—20–40%
- Seedling—40–60%
- Vegetative—60–90%
- Flowering—90–100%
You should purchase a grow light with at least 7000 lumens.
How Many Watts Do I Need For My Grow Lights?
Each LED light should have a listing that tells how many watts it takes to power the light. In addition, each light should have a unit of light intensity, reported as PPF (photosynthetic photon flux) or foot-candles (the amount of light received by a 1 sq. ft surface located 1 foot away from a light source is equal to one candle). Most grow lights fall in the PPF range of 10-50, and choosing the highest number you can find is important for tomatoes because they will be under the light for a long time, even if you are just starting seeds. Lower light intensity can cause leggy, weak stems.
Best Grow Lights For Tomatoes
The best grow light depends on the size of the area you are trying to light and whether it is the sole light available or there is some other light, such as from a window. These grow lights are meant for use in a house or greenhouse. They are not meant for use outdoors. I have used a lot of different grow lights to start seedlings and grow plants. These are the best ones I have found.
1. Spider Farmer SF4000 LED Grow Light – Best Large Area Grow Light
Spider Farmer SF4000 LED Grow Light is my pick for a grow light to cover a lot of space. This light covers a 5-foot by 5-foot area with white, blue, red, and infrared light. It consumes 450 watts and puts out a lot of light very efficiently. In addition, you can link several of these lights and control them with one dimmer switch. You can use the dimmer to determine the light intensity, so it is correct for every growth stage. Because these lights are cooler than fluorescent lights, no noisy fans are necessary. The light has fair waterproofing, so can be used in humidity up to 80%. The light looks fairly natural, so you can easily evaluate your plants. Spider Farmer provides five years of after-sale maintenance at centers in the United States. The light-emitting diodes are better distributed for optimal light strength throughout the light.
Spider Farmer products are made in China. The company started when horticulturists and engineers got together to change indoor growing.
Spider Farmer SF4000 LED Grow Light is the grow light to use if you have a grow room or greenhouse full of tomatoes. The lights hang from the ceiling. You can link them, so you dim them all with one switch. The one thing these lights do not have is a timer. However, you can use an aftermarket timer with them. These lights are expensive, around $475, but they are good lights. They should last over 55,000 hours, according to the manufacturer. The aluminum housing won’t corrode in the high-humidity environment needed to grow tomatoes indoors. Cables have a durable covering, so they won’t break easily, either. If I had room for a grow room, these are the lights I would use. They are easy to hang and easy to use. If I have any trouble with them, the manufacturer has repair facilities in the US and pledges to fix them for five years. The lights weigh 14 pounds, so you will need a strong chain to hang them from. Hanging them from a chain lets you raise and lower them as your tomato plants grow from seedlings to mature plants heavy with tomatoes. I appreciate the natural-looking light, so I don’t have to carry my plants outside to evaluate them.
Pros:
- Large coverage area
- All the important temperature light
- Very energy efficient
- Cool lights eliminate the need for fans
- Can link lights to one dimmer switch
Cons:
- No timer
2. Feit Electric Grow Light – Best Mounted Grow Light
Feit Electric Grow Light 19W 2ft LED for Indoor Plants and Gardens looks like a traditional fluorescent light you might use on a rack of plants. Instead, you get a 19-watt LED light that is much more energy efficient. The lights do not get hot, so won’t scorch your tomato plant’s leaves the way a fluorescent light can. The light is two feet long and comes fully assembled. This light has an intensity of 28 PAR, in the middle of the desirable range. The light shines with 450Nm blue and 655 NM red temperature, so is usable for both seedlings and mature plants. The cord is five feet long. This light is rated for high-humidity applications and has a three-year warranty. It is made in the USA. Up to eight of these lights can be linked to become one long light. The light has a life expectancy of 25,000 hours.
Feit Electric Inc. has been making lights for over 40 years. They have been family-owned since 1978 and work out of Pico Rivera, California.
Feit Electric Grow Light 19W 2ft LED for Indoor Plants and Gardens is intended to replace HID greenhouse lights or fluorescent lights for the serious plant hobbyist. Mounting hardware is included to hang the light from the ceiling or a rack. The advantage of this is that you can use chains to hang it and then adjust the height as the seedlings grow. This light will shine enough to make mature tomato plants have tomatoes.
I think the Feit Electric Grow Light 19W 2ft LED for Indoor Plants and Gardens is moderately priced for what you get, but it is still nearly $50. I have friends, however, who have a room full of plant racks, and this would work well in that situation. The energy savings over fluorescent lights are incredible. This light doesn’t heat up a room. This may be a disadvantage in the winter if you have depended on the heat from fluorescent lights to keep your plants warm. You can light up a big tomato plant with this light by hanging it on chains from the ceiling and raising it as the plant gets bigger. I also like the ability to string up to eight of these lights together to make one really long light.
This light doesn’t have a dimmer switch or a timer. However, you can get aftermarket dimmer switches and timers to plug in and add those features. There have been some reports of the light breaking after a few months, but I have not had that trouble.
Pros:
- Can replace traditional greenhouse lighting
- Won’t burn plants
- Has red and blue temperatures
- Can be linked in an eight-light chain
- Come assembled
Cons:
- Doesn’t have a dimmer switch or timer
- May break early
3. Aceple LED Small Grow Light – Best Budget Grow Light
Aceple LED Small Grow Light is inexpensive but has both blue light and red light. It is suitable for both seedlings and mature plants. It is a gooseneck lamp that clips on a table or baker’s rack. You can also stick it on or screw it into the wall. The on/off switch is easy to use. The gooseneck can be twisted so that it puts the light exactly where you want it. The Aceple LED Small Grow Light is best for a few tabletop plants rather than dense racks of plants. The red light is 630 and 660 nm, and the blue light is 460 nm. The gooseneck is 15.8 inches, the clamp can open up to 2 inches, and the cord length is 59 inches. The lamp draws 6 watts and has a rated life of 25,000 hours.
Aceple does not have a website that I could find, so I don’t know anything about the company except the lamp is made in China.
I like the Aceple LED Small Grow Light for the plants I have on the table or at the top of a baker’s rack. I wish the gooseneck was a little longer so I could direct the light more precisely. I also have to use a timer with this light because it does not have one. However, if I could not afford an expensive light, I would recommend this one. It has the correct temperatures of light to grow both seedings to transplant and to grow mature plants to harvest.
Because the light is small, it is better to illuminate a pot of seedlings rather than a tray of seedlings. If you are growing a large tomato plant indoors, this light won’t work well. It does not shine over enough area to shine on all the foliage of a big tomato plant. The cord is nice and long, so I can reach the wall plug without an extension cord. It does have one of those big plugs that can take up more than its share of space on an extension strip.
This light would also make a nice supplemental light if you wanted to grow cherry or grape tomatoes in a window during the winter. The light would give the tomato plant enough light in the evenings after the sun had set to continue bearing fruit all winter. The clip is big enough to go on the sill of the window over the kitchen sink. I would use a bar-shaped LED lamp like the GooingTop LED Grow Light to provide light on a big plant stand because I think more light would reach each plant. If you do use this lamp to shine on a longer plant stand, you will need to turn your plants each week, or they will bend toward the light in the middle.
Pros:
- Inexpensive
- Has blue and red spectrum
Cons:
- Small area of light
- No timer
- Gooseneck could be longer
How To Use A Grow Light?
Grow lights have to be used properly to work well. Here are the two crucial elements of using a grow light to grow tomato plants from seedling to harvest.
Height Above The Plant
Your grow light should be kept 4-6 inches above your seedlings. You will have to move the light up as the seedlings grow to maintain a distance of 4-6 inches. Once the plant starts to flower, increase the distance to 6-12 inches. You can tell the light is too far above the tomato plant if it is leggy or light green in color. The light is too close if the leaves scorch or the leaves are bleached.
Length Of Time Lights Are On/Off
Deciding how long to leave your grow lights on, or whether to leave them on all the time, can be complicated.
If you want to geek out on your grow lights, the easiest way is the daily light integral (DLI). Daily light integral (DLI) is the amount of PAR received each day as a function of light intensity (instantaneous light: μmol·m-2·s-1) and duration (day). It is expressed as moles of light (mol) per square meter (m-2) per day (d-1), or: mol·m-2·d-1 (moles per day). You can get a light meter that will estimate the DLI or use a phone app that uses your phone camera as a light meter. The DLI is like a rain gauge in that it accrues throughout the day. Tomatoes need at least 15 moles per day and preferably more than 20.
If you are just not interested in being that precise, you can leave the lights on 16-18 hours a day for seedlings and 14-16 hours a day for flowering plants. The lights should be off at least 4-6 hours a day at night because tomatoes do not do well with 24 hours a day of light.
Signs Of Low Light In Tomatoes
Here are some signs of low light in tomatoes. If your plants exhibit these signs, increase the intensity of light by lowering your lights or using more powerful lights.
- Tomato leaves go from dark green to pale green to yellow to white.
- Plant stems become leggy, meaning the stems get long and thin and try to reach for the light.
- The distance between the leaf nodes on the stem becomes longer.
- Leaf drop, especially in older plants, may occur.
- Tomato plants may fail to produce flowers or set fruit with inadequate light.
Signs of Too Much Light In Tomato Plants
Too much light can damage your tomato plant. The two principal signs of too much light are leaves that appear scorched or bleached, and leaves may become chlorotic or yellow, without four to six hours of darkness each night.
Final Verdict
The best way to grow tomato plants indoors is to use an LED grow light. If you are just starting seeds, you can use a blue/white light. If you are growing the tomatoes indoors to harvest, you will need a light with both a blue/white light and a red light. Seedlings need 16-18 hours of light a day, and blooming plants need 14-16 hours a day. The lights should be 4-6 inches above seedlings and 6-12 inches above mature plants. If you are on a tight budget, my pick is Aceple LED Small Grow Light. If you want a traditional mounted light, my pick is Feit Electric Grow Light 19W 2ft LED for Indoor Plants and Gardens. If you have a large area of plants to light, my pick is Spider Farmer SF4000 LED Grow Light.
