Grow lights are an amazing solution for plants that don’t get enough sunlight. What’s important to know before you choose growing lights for your plants? Why do plants even need light?
We presented these questions and more to Amanda Lander.
Amanda is an enthusiastic gardener with experience gardening in two very different climates. She has a passion for all things green and growing, especially native plants and their many uses. She tries and tests all she learns and loves to share that practical, proven knowledge with others
Amanda, could you explain what are growing lights?
Growing lights are electric lights that simulate sunlight. They are mainly used for indoor plants.
Grow lights are necessary when your indoor plants are not getting enough sunlight or when you want to grow plants that require weather conditions different from your climate.
- For indoor plants receiving low light or no light, use a full spectrum grow light with 7000-7500 lumens and 32 watts per square foot.
- For seedlings, start with red lights then add blue as they emerge, or simply use full spectrum lights, with 2000-5000 lumens and 11-32 watts per square foot.
- For flowering plants, use red lights from 5000-10000 lumens and 32 watts per square foot.
- For full-sun plants, use full spectrum lights from 7000-10000 lumens and 32 watts per square foot while indoors.
- For shade-loving indoor plants with no light, use full spectrum grow lights from 5000-7500 lumens and 11-32 watts per square foot.
Plants need light for photosynthesis. They use this process to convert light, oxygen, and water into carbohydrates. The carbohydrates are then used to energize the plant, making growth, and flower and seed production possible.
The amount of light necessary depends on the plant. Typically, fruiting or flowering plants need more light than those that don’t, but the best way to know is to read the tag or look up the specific plant online. Learning about the plant’s natural habitat will give you a clue as to its needs.
For each plant, we must consider the duration, intensity, color, brightness, and temperature of the light it needs.
Grow lights should be left on 8-12 hours a day to be effective. Plants need a light/dark cycle for proper growth and development so lights should not be left on all the time.
The number of hours of light can and should be adjusted for your plants’ specific needs. For instance, vegetable plants and garden flowers normally prefer a longer “day”. They will grow pale and leggy if they get less than 14-18 hours of light per day.
Intensity is measured in wattage and refers to the strength or power a light emits. Light intensity is closely related to plants’ yields and quality. Grow lights should be intense but not hot.
Lumens are a unit of measurement of the brightness of light visible to humans. The more lumens, the brighter the bulb. However, brighter doesn’t always mean better for plant growth.
Spectrum refers to the wavelengths of light including all the colors we can and can’t see. The colors range from ultraviolet (UV) to infrared. Different colors affect the ability of plants to photosynthesize.
PAR stands for Photosynthetically Active Radiation and it describes the wavelengths of light that are important for photosynthesis. Scientists have determined through experimentation that blue and red light are particularly useful to most plants. Research is still being conducted to understand this information better.
The difference between red, blue, and white light is how each part of the spectrum can affect plant growth. Red light is the longest wavelength and blue is the shortest. Red and blue wavelengths seem to have the greatest effect on photosynthesis.
White light is broad-spectrum light containing all the colors. Plants use the full spectrum in photosynthesis so white light is recommended for indoor plants. Many grow light kits include white light with additional red and blue bulbs for optimum efficiency.
Red and blue light are best for plant growth. These two wavelengths are often used to boost productivity in large outdoor greenhouses where plants receive normal sunlight. It is not enough to use only red and blue grow lights because plants use all the colors for photosynthesis.
The best lights for growing seedlings concentrate blue light. Blue and purple are the most important wavelengths for beginning vegetative growth.
The best lights for mature flowering plants are red and blue. The red wavelength is necessary for blooms to form and is most effective when it is combined with blue.
The best lights for growing food are full-spectrum or white lights. Broad-spectrum lights include blue light that is best for green growth, red light that is necessary for fruiting and flowering, and all the wavelengths between that support photosynthesis.
There are many different types of growing lights including LED, HID, and fluorescent. The best lights for growing plants indoors are LED and fluorescent. Though it is available, incandescent light is not a good choice for growing plants.
LED stands for Light Emitting Diode. These are the most efficient lights to use for growing though they may cost a little more upfront. They can be very intense but emit almost no heat. They are available in white, red, blue, or a combination of the three.
Fluorescent lights are another great choice for grow lights because they are efficient, widely available, inexpensive, and emit the necessary spectrum for growth. Fluorescent tubes and Compact Fluorescent Lights (CFL) are both effective for plant growth and emit very little heat.
Incandescent lights are not a good choice for growing lights because they are less energy efficient, emit a lot of heat, and do not produce sufficient intensity or blue wavelengths for plant growth. Except for low-light plants like dracaenas, plants under incandescent lights will not thrive even if they survive.
The main difference between grow lights and regular house lights is the spectrum. Normal lighting fixtures do not produce the wavelengths needed for photosynthesis. Normal bulbs, including incandescent lights, are often bright but not intense enough for plant growth and emit more heat which can burn leaves.
To choose a growing light for your plant, consider the following checklist:
- Light availability- will the grow light be a sunlight supplement or replacement?
- Light preferences- does your plant thrive with more or less light?
- Garden size- what size light will you need to nourish all your plants?
- Spectrum- does this light emit the wavelengths necessary for plant growth? Is your goal to promote flowering or green growth?
- Heat- will this bulb burn your plants’ leaves?
- Intensity- is the wattage high enough to help plants flourish?
- Cost- is your priority to minimize upfront cost or long-term energy efficiency?
All light-loving indoor plants benefit from growing lights. This includes popular house plants, such as:
- Peace lily
- Fiddle leaf fig
- Spider plant
Indoor vegetables, including:
- Cherry tomatoes
And flowers, like these:
- African Violets
You can buy growing lights online at indoor gardening stores, like Gardener’s Supply Company;
The grow lights below have been tried and proven effective for home use.
These lights appear white to the human eye which may be a better choice for those prone to photosensitive headaches.
- The GE Grow Light bulb can fit into any standard light fixture and blends well with existing decor. It is a full spectrum grow light and will promote your plant’s health.
- These Plant Growing Light Strips by Lightimetunnel are convenient and provide all the wavelengths necessary for all stages of growth.
These growing lights appear pink to the human eye because they concentrate on red and blue wavelengths. They provide other colors in the spectrum to a lesser degree. Some people find that pink lights in their living space can give them headaches but they are very effective at growing beautiful healthy plants.
- These brandless 45W LED Grow Light Full Spectrum Panels come in a set that is easy to install and excellent for seedlings.
- Barrina LED Full Spectrum Linkable Grow Lights are larger than the others on this list but still very suitable for home use and highly effective.
Grow lights can greatly enhance growth even in plants that receive regular sunlight. They are indispensable for indoor plants lacking any amount of light exposure. When selecting growing lights for your plants at home, be sure to purchase those that will provide the full spectrum needed for healthy plant growth and production, especially red and blue wavelengths.
We asked Amanda a few other questions you might find interesting: