Of course, all plants need light, but the amount they need can vary widely. A space with sunny windows may be what all your low-light houseplants need to do well, but other houseplants need brighter, more consistent light to grow properly. For example, if you’re growing vegetable seedlings for your spring garden, coaxing flowering houseplants into bloom, or even growing fresh herbs on your kitchen countertop, the right grow light is your friend. In this article, we’ll cover why plants need light, and the best lights for growing plants.
Photosynthesis is the process by which plants convert water and carbon dioxide into food (sugar) when exposed to sunlight. Plants take carbon dioxide from the air through openings in their leaves and convert it into sugar during photosynthesis. Chlorophyll is the green pigment in plants that enables plants to create their own food and also gives plants their green color. Water is necessary for plants to perform photosynthesis, and plants absorb water through their roots. Oxygen is released back into the atmosphere as a byproduct of photosynthesis.
Light duration, or the amount of time a plant is exposed to sunlight, is also important. The duration of light varies with the seasons. This also affects the ambient temperature. Summer sunshine time is the longest, followed by spring and autumn, and winter sunshine time is the shortest. Not all plants need the same amount of light. Fruiting plants, such as tomatoes, tend to require more sunlight than non-fruiting plants. For example, strawberries require more sunlight to grow than lettuce. Fruiting plants grow best in summer and may require up to 18 hours of light a day to bloom and bear fruit. On the other hand, some plants, such as cauliflower and cabbage, grow well in late fall with as little as 12 hours of light a day.
What to Consider When Choosing the Best Lights for Growing Plants?
Whether you’re looking for grow lights to supplement the natural light for your houseplants over the winter, or you’re looking to start seeds indoors for transplanting into your garden in the spring, grow lights can help. Options today range in price from $20 to $150 or more, depending on the quality and range of light.
Cool, warm and full spectrum
Grow lights are marked with numbers like 2,500K or 6,500K, which tell you the temperature of the light based on the Kelvin measurement scale. The higher the number, the cooler the light. So a bulb with a Kelvin rating of 6,000K will appear white or blue, while a 3,000K bulb will be more yellow. Each type of light — warm or cool — stimulates specific plant behaviors.
If your goal is to improve the foliar growth of houseplants or grow leafy greens or seedlings, choose cooler-spectrum bulbs around 6,500K. Warm light has a lower Kelvin rating and is ideal for indoor plants and flower production for fruit trees such as citrus. When in doubt, full spectrum lights take the guesswork out and offer a combination of cool and warm light for the best of both worlds.
The electromagnetic spectrum is the wavelength or frequency range over which electromagnetic radiation extends. The electromagnetic spectrum consists of the visible spectrum (the types of light we can see) and the infrared spectrum (the types we cannot see). The four seasons have different light durations, which can affect photosynthesis. Certain colors of light are more important for photosynthesis than others. Plants are adapted to absorb and utilize the right amount of light in order to grow naturally outdoors.
When growing plants indoors, we must reproduce the light produced by the sun, keeping two important factors in mind: color temperature and duration. The temperature of a color on the electromagnetic spectrum is measured in Kelvin.
Unlike the bulbs in a chandelier or sconce, grow lights emit a spectrum similar to the sun.
“Grow lights allow indoor growers of any size to bring the right spectrum to their plants,” said Roger Buelow, CTO of AeroFarms, a high-tech vertical farming company that grows produce indoors year-round.
“Technically, plants don’t need sunlight. They need the proper spectrum,” he explained, adding that plants are actually quite picky in this regard. Their chloroplasts photosynthesize only a narrow bandwidth of light, which grow lights can provide.
Grow lights also emit less heat than traditional light sources, so they’re less likely to scorch your plants
You can start seeds indoors using grow lights before spring, care for outdoor plants that have been moved indoors for the winter, or grow plants indoors year-round. They also act as stand-in windows for those who live in darker homes and need some help keeping sun-loving houseplants alive.
Plants grow best when exposed to light as similar as possible to natural sunlight, with temperatures between 2,700 and 7,000 Kelvin. In the past, growers have used red and blue LEDs to provide plants with the full spectrum of light they need to grow. The only reason to use red and blue LEDs is that white LEDs that provide the necessary spectrum and brightness do not yet exist. With new technology, however, it is entirely possible to get the full spectrum and brightness that plants need, 2,700 to 6,500 Kelvin, and white LED lights. White LEDs use the least amount of power, last the longest, and grow plants like all other types of light available today.
Not only is red and blue light unnecessary, it can actually disrupt sleep and make some people feel nauseous. Blue light affects the body’s levels of the sleep-inducing hormone melatonin more than any other wavelength, which is why it’s recommended to avoid electronic devices before bedtime.
Types of Grow Lights
Both LEDs and fluorescent bulbs produce the full spectrum of light that plants need to grow. There are many grow light kits on the market that include LED or fluorescent bulbs, but LED systems offer some advantages that make them a better choice. First, while LED bulbs cost more to buy than fluorescent bulbs, they use half the amount of electricity and last five times as long as regular fluorescent bulbs. They also emit less heat, and mercury-free LED tubes don’t shatter like glass fluorescent tubes, reducing safety concerns.
What type of light bulb to buy?
The most common types of grow bulbs are T5 and T8 LED tubes. Bulbs are most commonly (more or less) 6,500 Kelvin, which is the color temperature of light we see in daylight. Traditionally, blue light would be used to provide plants with this necessary wavelength. Plants do vegetative growth during the day, so this light is beneficial to plants during the vegetative growth phase.
Bulbs of about 2,700 Kelvin are beneficial for plants in the flowering and fruiting stages of growth. This is the color temperature at sunrise time of day. 2,700 to 2,700 Kelvin bulbs are traditionally warmer in color, with more red and orange tones. The red lights used by some growers will transmit this color temperature to the plants.
Both 2,700 and 6,500 Kelvin lamps are available as white LEDs, so red or blue lamps are no longer required. We recommend using fixtures that hold four bulbs and alternating 2,700 and 6,500 Kelvin bulbs in the fixture. This will ensure the plant gets the benefits of both.
LED lights are also available in 4,100 Kelvin and 10,000 Kelvin. While you’ll probably never need these types of bulbs, they’re worth mentioning. Providing 4,100 Kelvin, the bulb is a neutral light that promotes leaf and stem growth. This type of light does not do much for plants in the vegetative or flowering growth stages.
The bulbs used above the aquarium are typically 10,000 Kelvin. Note that this is the bluest light in the electromagnetic spectrum. This is also similar to the light spectrum visible deep underwater, which makes it useful for growing aquarium plants or raising fish.
LED and Fluorescent Bulbs
Standard fluorescent bulbs are a weak household light source, but they’re great for supplementing natural light on houseplants or seedlings. Their cooler light makes them one-dimensional, so they’re ideal when the goal is dense foliage rather than flowers. Because their light cannot penetrate plant leaves with intense intensity, growers must position the light within a few inches of the top of the plant to be effective.
Full-spectrum compact fluorescent lamps (CFLs) are a better choice. CFL grow lights come in both tube and bulb forms and are more intense than standard fluorescent lights.
Not to be confused with regular LED lights, LED grow lights are more expensive than fluorescent lights, but they make up for this with longevity and energy savings. LEDs have blue and red light to mimic the full spectrum of the sun and may emit a bright purple glow. It’s not a big deal if the lights are in the basement or garage, but it’s worth considering if they’re in the living area. Like fluorescent bulbs, LEDs can be packaged in tubes and used to illuminate a tray of seedlings, or used as bulbs when you want to illuminate specific plants.
The number of plants or nursery trays you want to grow is a good indicator of the type of grow light that is best for your situation. While it’s perfect for placing individual bulbs over sun-loving succulents in winter, seedling trays are better for a stand system that lets you boost the light as the seedlings grow taller. So, whether it’s a prefab stand with lights, or one built from scratch using cheap wire racks and a hanging grow light strip or two, in the end, your budget will have the final word.
Pre-made booth setups are expensive, and if you don’t have high seed startup plans, consider building your own system. However, indoor plant lovers may gravitate towards more aesthetically pleasing prefab grow light stands that are better suited for indoor living spaces.
For indoor plants, consider attaching full-spectrum grow lights to bendable or gooseneck arms so you can place the lights directly above the plants. Some are fixed lights for tabletops, and some have a clip on the end of the bendable arm so you can attach the light to the edge of a table or table. These lights are designed to be used with one or two houseplants and usually come with a timer so you can meet the plant’s specific lighting needs and a USB connector for plugging into a computer.
For seed-starting and flowering houseplants, some full-spectrum grow light panels come with timers and remote controls that allow you to vary the type of light emitted based on the plant’s growth stage – cool light for seed start, warm light for flower production, and full Spectrum, when you’re not sure what type of light you need.
The Best Lights for Growing Seedlings
Newly emerged and seedlings grow well with the help of full spectrum light with blue and red wavelengths. Special LED and fluorescent “grow lights” can be used, but so can less-expensive fluorescent tube bulbs. Make sure the light source is within 6 inches of the plant leaves for best results. For easy mobility, hang the fixture on a chain or place your plant on a table or this DIY seed starter. To keep your lights working efficiently, lightly wipe the tubes to remove dust and grime before each year of use.
Optimal Light for Flowering Plants
Red light waves are essential for prompting plants to bloom and growing fruit indoors. Shop for LED bulbs and fixtures designed for growing plants. They’re often labeled “grow lights” because they’re designed to produce lots of red light waves.
Some electrical brands make plant-friendly LED bulbs called “high output LEDs.” High output LEDs are typically twice as bright as standard LED grow lights. These ultra-bright lights are ideal for growing plants native to sunny, dry climates, such as cacti, citrus, rosemary, and geraniums. Plan to light 16 to 18 hours a day for flowering and fruiting plants. Position the light source about 12 inches away from the leaves.