Using Grow Lights: 9 Expert Tips

Grow lights are a must-have if you want to start seedlings indoors during the dark days of winter or shine extra light on your indoor citrus tree. But choosing and using them correctly can come with learning hurdles!

Throughout my years of reading about grow lights and using them to grow plants, I’ve learned a few tips on how to use them. Whether you’re confused about the differences between LED and CFL lights or are wondering how long to leave your lights on, I’ve got you covered. Stay with me to learn nine tips for using grow lights.

Position Lights Close to Your Plants

One of the biggest mistakes beginner growers make when using grow lights is setting them too far away from their plants. This is especially true if you’re using them for seedlings. While the exact distance between the grow light and the plant varies, most plants will remain happy if you place grow lights 6-18 inches above them.

If your grow light is too far away from your plants, you’ll likely notice signs of light deprivation. Seedlings may become long and spindly, while mature plants often experience slowed growth and small leaves. Moving the light closer to your plant will help provide the plants with more light.

As plants grow, the distance between the grow light and the top of the plants will decrease. Move your lights up so the space between the lights and the plants remains the same. Some have built-in systems that simplify repositioning, while others require you to manually raise the lights using chains.

Set the Lights on a Timer

Before I had my grow light game dialed, I manually turned my lights on and off each day. Or at least I tried to. I can’t tell you the number of times I went to bed and woke up in the middle of the night, remembering my lights were still on!

While you may think more light is better, many plants grow best when they have a dark period to rest and reset. Most plants thrive when they receive 12-14 hours of bright light each day, so you should aim to set your grown lights on this schedule.

Some lights come with a built-in timer that makes it super easy to manage your lighting schedule. However, you can set any light on an automated schedule with the help of a basic plug-in light timer.

Pay Attention to the Light Spectrum

When choosing a grow light, the light spectrum is one of the most important aspects to pay attention to. Also known as the light color, the spectrum refers to the wavelength of light as measured in nanometers. Humans can see light between 380-750 nm, so lightbulbs emit light in this range. 

When we’re talking about wavelengths and plants, photosynthetically active radiation (PAR) is an important term to keep in mind. PAR occurs from 400-700 nm and refers to the range of light plants can use to complete photosynthesis. Plants also rely on light in this range to determine when to complete processes like germination, stem elongation, and flowering.

Most plants prefer full-spectrum lights. These lights contain the entire visible spectrum and provide all wavelengths of light in the PAR range.

Consider Light Temperature

It seems there are countless ways to measure and describe lights. If you browse the lighting aisle at your local hardware store, you’ll see packages describing watts, lumens, spectrum, and more! While all of these words tell you something about the light, some are more important than others when it comes to choosing the right grow light for the job.

The Kelvin (K) scale describes light temperature and ranges from 1,000 to 10,000 K. Lower numbers indicate warm light, and higher numbers correspond with cool light. The best grow light temperature depends on the type of plant you’re growing.

Since cool light spurs vegetative growth, it’s the best option for seedlings or vegetative houseplants like jade and croton. If you’re not concerned about flowers, choose a grow light with a temperature between 5,000K and 7,000K.

Warm light encourages flowering, so choose a warm, full-spectrum light if you’re growing flowering plants like bird of paradise and Meyer lemon. A light with a temperature between 3,000K and 5,000K will provide plants with cool light for vegetative growth and warm light for flower production.

Be Aware of the Different Types of Lights

Along with looking at a light’s spectrum, temperature, and power, consider the type of light. As technology has advanced, more and more lights have come onto the market. You have three main options: light-emitting diode (LED), compact fluorescent lamp (CFL), and high-intensity discharge (HID).

LEDs are one of the top choices due to their energy efficiency. Not only do LEDs use little electricity to produce light, but they also lose very little light as heat. LEDs cost more than other options upfront but also have a long lifespan. LEDs are excellent options if you’re planning on keeping them for over a year or two.

CFLs were the first major alternative to standard incandescent bulbs. Although they’re more efficient and last longer than the old incandescent bulbs, they still release around 80% of their energy as heat! Not only does this mean they aren’t the most energy-efficient, but you also have to account for this heat when growing plants. However, CFLs are less expensive than LEDs.

HID lights are your last major option. Both high-pressure sodium and metal halide lights are types of HID lights. These lights cost less than LED lights but produce more heat and don’t last as long.

Remember that Plants Require More than Light to Grow

If you notice your indoor plants look sad, don’t assume improper lighting is to blame. Remember, plants need a long list of elements to remain healthy! Improper soil mix, cold temperatures, too little or too much water, and many other factors can stress your plants and lead to stunted growth and discolored leaves.

Looking at the entire picture is especially important when you’re growing seedlings. These tender plants are extra susceptible to minor environmental changes, so a 10-degree swing in temperature or a day without water can lead to seriously wilted leaves or discoloration. Of course, a lack of light can also prevent plants from reaching their full potential!

Knowing the signs of lack of light can help you determine when you need to alter your grow light setup. Seedlings often develop spindly, elongated, weak stems as they search for light—in other words, they become leggy. Mature plants often exhibit slowed growth and may drop older leaves.

Clean Regularly

Less light will reach your plants if your lights become covered in dust or condensation. Therefore, make it a habit to clean them once a month. 

The best cleaning method depends on the type of light. You can wipe plastic tube lights down with a wet rag, but a feather duster is often best for more delicate lights. The goal is to remove any residue without damaging the lights, so use your best judgment when selecting a method.

Choose the Proper Light Size

Along with considering light type and temperature, pay attention to light size. While it’s easy to choose a small grow light due to its low price tag, remember that grow lights should sit no more than 18 inches above your plants. If you need to raise your lights higher than this to illuminate all of your plants, choose a larger light or add more lights to your setup.

While small, single-bulb grow lights aren’t the best option for 10×20 trays of seedlings, they can work well for individual houseplants. Adding a few smaller ones throughout your home also looks better than installing a large group of shop lights.

If you’re using multiple lights to cover a wide space, make sure the lights are close enough together to create a continuous supply of light. For example, many commercial growers’ indoor seed-starting setups consist of 48-inch shop lights hanging from a 48-inch wide metal shelving unit. Since these shelves are 18 to 20 inches deep, growers must hang multiple lights to supply this area with light. I’ve hung three shop lights six inches apart with great success.

Don’t Let Fear of Failure Stop You

I was immediately overwhelmed by all the options and terminology when I started learning about grow lights. Words like lumens, watts, and Kelvins swirled through my head and turned my previous excitement into dread. How would I possibly choose the right grow light for my plants?

However, when I took a step back and realized any light would be better than no light, I felt better. And it turns out the lights I picked out have worked just fine over the past five years!

That’s not to say you shouldn’t learn about the best type of light for you. But if you don’t understand all the nitty gritty grow light terminology, don’t sweat it! The most important thing is that you provide your plants with some kind of light. And if you still feel lost, order a grow light from a trusted company and return to gardening!