Indoor lighting simplified and the new SpotOn® Quantum PAR Light Meter

Indoor gardening is increasingly popular among home gardeners as well as professional growers. Plants grown indoors and undercover in a greenhouse extends the season and offers control of the environment much better than growing outside, where plants can be damaged by the elements. 

Home gardeners have traditionally used grow lights for starting a few flower and vegetable transplants or to add supplemental lighting for houseplants. However, the food, flower and medicinal palette has expanded quite a bit in recent years, prompting people to consider growing things like microgreens, hydroponic lettuce, and legal cannabis indoors under lights. 

An interest in grow lights

This has spawned an interest in grow lights, particularly LED’s. It has also spawned a lot of confusion over what the best light is for different growing conditions. Most of this confusion, I believe, is over the different terms used to describe light. So let’s see if we can dim the confusion about lights and simplify things. This way you, the grower can make the best lighting choice possible for your indoor growing situation. I’ll also introduce you to an affordable light meter that will ensure that your plants are receiving optimum light from light fixtures and through greenhouse coverings. 

Understanding the terms

It’s important to understand the terms used to describe light fixtures so you know what you’re buying. Terms like watts and lumens have really stuck in the minds with the consumer; however, they don’t address the quality and kind of light needed for the different growing phases of plants. 

Watts only speaks to the energy a bulb is using and lumen refers to the brightness and efficiency of a lamp. Since plants see light differently than us humans, the measure of lumens is irrelevant when it comes to selecting a good lamp for your growing operation. 

In the spirit of the phrase “keep it simple stupid” I can tell you that there are only a few terms and concepts we need to learn to make better lighting choices.

Veg or flowering?

In Leslie Halleck’s book on lighting, Gardening Under Lights: The Complete Guide for Indoor Growers, she does a great job explaining artificial light that will help the reader make better lighting choices. book on lighting

Light in the blue spectrum has a short wavelength and is used in the veg state of growing when you’re only concerned with establishing green growth. Light in the red spectrum has a long wavelength and is used in the flowering stage. Cannabis growers use lights in the red spectrum when their plants are in the flowering stage.

I’ve always used a standard flourescent shoplight (T12) to start my tomato and pepper transplants and a few flowers. However, a few years ago I picked up a relatively inexpensive T5 flourescent fixture with 5 flourescent bulbs or tubes. Compared to the T12, the T5 delivers more usable light than a T12. It is used when your plants are in the nonflowering or veg state. If I wanted them to flower and set fruit indoors I’d have to obtain a grow light that delivers light in the red spectrum. 

There are LED fixtures on the market that, rather than having to change from a “veg” bulb to a “flowering” bulb, you can simply flip a switch. Prices range from $100-$200, which is much cheaper than what LED light fixtures were selling for just a few years ago. Plus, LED light bulbs last longer than fluorescent and high-pressure sodium bulbs used in traditional lighting; they also put out much less heat than do high-pressure sodium bulbs, which can literally scorch plants if the plants get too close to the fixture. 

Understanding Photosynthetically Active Radiation

 One measure of light that is critical to growers and can be measured with a meter is PAR (Photosynthetically Active Radiation). PAR is a measure of the usable light plants have for productive growth. When you purchase lights, especially the more expensive type, the manufacturer should be able to provide you with the PAR range of the light fixture. PAR is a measure of the quality of light and is measured in micro mols per second. PAR readings for a light fixture should be between 400-700 and may fluctuate, which is okay. Like measuring pH, if PAR is in the acceptable range you’re all set.  

New light meter hits the market!

There is a new light meter that has hit the market which I think should appeal to small and large growers alike. I’ve had the pleasure of trying out the SpotOn Quantum PAR Meter, by Innoquest, Inc. Quantum PAR meters can be VERY expensive, but this one is being sold at a reasonable cost ($295 vs. up to $1500 for some meters). It is very easy to use and gives readings for both PAR and Daily Light Integral (DLI), which is the cumulative reading of PAR for any given period. DLI is a measurement that is very important because you can determine the total number of PAR units that reach your plants during the time your lights are on; it can also be used to determine the PAR in your greenhouse on a typical day.

Taking light readings in a greenhouse

PAR and DLI are important readings to take in a greenhouse where coverings, especially older coverings, can reduce the amount of light that actually reaches and is usable to a plant. AND, it can help you determine if it is time to replace your covering

This is an intentionally oversimplified description of light and how to measure it. If you want to learn more about lighting and the light needs of specific plants, I urge you to pick up a copy of Halleck’s book. The SpotOn Quantum PAR Light Meter can be ordered directly from Innoquest Inc.  Halleck’s book and the SpotOn Quantum PAR Light Meter is all you will need to make good choices for lighting and greenhouse coverings. 

Neil Moran is a copywriter helping green industry companies increase profits by writing effective press releases, blog posts, articles, and social media and email marketing.  

Disclaimer: I’m currently helping with marketing the SpotOn Quantum PAR Light Meter. 


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