Grow Light Guide

The Coco for Cannabis Grow Light Guide is an independent resource for growers. Our goals are to demystify grow light metrics, share reliable grow light data and empower home growers with the best information about grow lights. We conduct independent grow light field testing and have developed articles and resources to help growers understand the science of horticultural lighting. In this guide, we publish complete grow light field test data, describe the science behind our testing protocols, explain what all the data means, provide grow light calculators to help analyze and compare grow lights and share articles about horticultural lighting that are grounded in the sciences of physics and botany.

The Science of Horticultural Lighting

In these articles, we offer straight forward explanations of the science behind horticultural lighting.

  • Grow Light Metrics Primer

    Learn about the science of horticultural lighting. We explain the key grow light metrics and terminology: PAR, PPF, PPFD, and more. Start here to make the most of our Grow Light Guide!

  • How Much Light (PPF) Do You Need for Indoor Cannabis?

    We review the science of cannabis photosynthesis and explain the optimal quantity (PPF) and density (PPFD) of light for indoor cannabis. Not enough light leads to “larf” and too much light can result in photoinhibition. We include a Grow Space Calculator which shows the optimal light and harvest potential for any grow space.

Grow Light Comparison & Evaluation

Grow Light Comparison and Evaluation is the core of our grow light guide. Our grow light calculator allows you to compare and analyze different grow light fixtures. The articles below explain the formulas that we use to calculate efficiency, coverage and harvest potential for different grow light fixtures.

  • Grow Light Calculator

    Our grow light calculator provides an accurate way to analyze and compare different grow light fixtures. You can enter your own grow light data or select a preloaded fixture. The Calculator will tell you the Usable PPF, Efficiency, Coverage and Harvest Potential. The Grow Light Comparison Table allows you to easily compare different fixtures.

  • Calculating Grow Light Efficiency, Coverage & Harvest Potential

    We explain how to use the Grow Light Calculator, the formulas it uses and the science behind them. It is time to move past only using wattage to evaluate lights! Learn how we use Usable PPF to calculate our efficiency ratings, coverage estimates, and benchmark harvest targets.

Grow Light Testing

We conduct independent grow light PAR testing and publish all of the results in our Grow Light Field Test Reports. Read our Grow Light Testing Protocol to understand how we do our tests and why we think they are the best reflection of how grow lights will perform. See our Grow Light Field Test Reports below.

  • Grow Light Testing Protocol

    Field testing produces the most accurate measurement of Usable PPF, but it must be done correctly. In this article, we explain our testing protocol and the science behind it. Learn about test area size, the importance of reflective walls, and the scientific way to determine optimal hanging height.

My latest video project is on The Science of Horticultural LEDS! For the first time ever, I, Dr MJ Coco, appear in person, on camera in this video!

LEDs are the Present and Future of Horticultural Lighting! However, there is a lot of misunderstanding and misinformation about horticultural LEDS. In this video, I do a deep dive into the science of horticultural LEDs. I explain the Physics of Light Emitting Diodes and the latest horticultural science about photosynthesis, spectrum, and plant development, including cannabinoids.

I have been working on this video for months! I hope that you all enjoy it!

The Best 5x5 Grow Light: 9 Fixtures Tested, Analyzed, Compared, and Ranked

In 2021, I tested 9 grow lights that are designed and marketed for 5x5 coverage. In this video, I review each fixture for components, build quality, performance, and cost. Then I rank and compare them. Watch the video to see which has the Best Quality, which has the Best Performance – for grows with and without supplemental CO2, which has the Best Price, and which is the Best 5x5 Grow Light Overall.

Grow Light Physics: Coverage Area & Running Arrays

Come explore the Grow Light Physics of Coverage Area and Running Arrays! I play with one and two of the new Mars-Hydro SP-3000s in different coverage areas. I use 5 different PAR tests to explain and explore some of the key aspects of Grow Light Physics.

Watch the Video on YouTube.

The New Mars Hydro SP-3000 is an impressive fixture! However, the video is really about Grow Light Physics, the SP-3000s are just the stars of the show. The physics that I cover is helpful to understand, whether you plan to run the SP-3000 or any other fixture. I hope it really helps to clarify the way that light works in a grow space.

I explain all the key metrics and show how we use them to test and evaluate grow lights. I hope that all growers will find the video interesting, regardless of how much experience you have with grow light physics!

Field Tested LED Grow Lights

Grow Light Discount Codes

Atreum Lighting Discount Code: CCFC


Use Code: CCFC

10% Discount

Cultiuana Discount Code: CCFC


Use Code: CCFC

10% Discount

ChilLED Tech Discount Code: ChilledCoco


Use Code: ChilledCoco

10% Discount

Mars-Hydro Discount Code: CCFC


Use Code: CCFC

3% Discount

Medic Grow Discount Code: CCFC


Use Code: CCFC

10% Discount and Free Shipping in the Continental US

Photontek Discount Code: CocoPTK


Use Code: CocoPTK

10% off on top of any other discounts

Spider Farmer Discount Code: CCFC


Use Code: CCFC

8% off on top of any other discounts

ViparSpectra Discount Codes

Shop Amazon: US AmazonCanada Amazon

Enter Discount code DrMJCoco at checkout on Amazon

3% off on top of any other discounts

Special Discount code for the New XS1500 PRO: DrMJCocoPRO

8% off the XS1500 PRO on top of any other discounts

Unbiased Testing & Reviews

We offer this guide as a resource to growers. We do not accept advertising. Grow light manufacturers may send us lights for testing. However, we receive no compensation from manufacturers for testing or for including their fixtures in our guide. We will always report accurate information and give our honest evaluation of each fixture.

You can support our work by following our links and using our discount codes when you make a purchase. As an Amazon Associate, we earn from qualifying purchases. However, we have no financial interest in promoting any particular brand of light. Our recommendations are based on the science, testing and our honest evaluation. We want to provide you with the knowledge and information so that you can make the best grow light decisions for your cannabis grow.