• Skip to main content
  • Skip to secondary menu
  • Skip to primary sidebar
  • Skip to footer

Grow Light Info

Helping You Choose the Right Grow Light

  • Grow Lights
    • LED Grow Lights
      • Buying Guides
      • Reviews
        • BestVA DC Series Review
        • HLG Review
        • KingLED Review
        • Mars Hydro Review
        • Phlizon COB Series Review
        • Spider Farmer Review
        • Viparspectra Review
      • Tips & Advice
    • HID Grow Lights
      • Buying Guides
        • Best CMH Grow Lights
        • Best HID Grow Lights
        • Best MH And HPS Bulbs
      • Tips & Advice
    • Fluorescent Grow Lights
      • Buying Guides
        • Best T5 Bulbs For Veg
        • Hydrofarm AgroBrite T5 Review
      • Tips & Advice
    • Grow Light Guides
      • Adjustable Grow Light Stands
      • Best Lights For Vegging
      • Best Lights For Flowering
    • Tips & Advice
  • Grow Tents
    • Grow Tent Buying Guides
      • Best Large Grow Tents
      • Best Small Grow Tents
      • Quictent Review
      • Secret Jardin Review
      • Vivosun Review
    • Grow Tent Info
  • Seeds
    • Best Place To Buy Marijuana Seeds
    • Best Autoflower Seed Banks
    • Highest Yielding Autoflowers
    • Seed Banks That Take PayPal
    • Crop King Seeds Review
    • ILGM Seed Bank Review
    • Marijuana Seeds NL Review
    • Seedsman Review
  • Other Equipment
    • Best Digital Scale For Weed
    • Best Fan For Grow Tents
    • Best Humidifier For Grow Tents
    • Best Microscope For Trichomes
    • Best Scissors For Trimming Weed
    • Best Timer For Grow Lights
  • Indoor Growing
    • Cannabis Cultivation
  • Cannabis Info
    • Useful Info
    • Fun
You are here: Home / Grow Lights

How Many Grow Lights Do I Need? (Easy Way To Figure It Out)

Last updated February 21, 2024 By Steven Leave a Comment

How Many Grow Lights Do I NeedSetting up a cannabis grow is not cheap.

You will have a good-sized list of equipment to buy.

And the most expensive equipment you need are the grow lights.

Naturally, you would like to buy as few of them as possible.

But you also want to ensure your plants get the light they need.

The obvious question is: how many grow lights do I need?

Keep reading to find out. How many grow lights you need depends on a number of factors. We will guide you through the process of figuring out your plants’ lighting requirements and how best to meet them.

Contents

  • 1 How Many Grow Lights Do I Need?
    • 1.1 Cannabis Lighting Requirements
      • 1.1.1 Light Intensity And Spectrum Requirements
      • 1.1.2 Different Growth Stages And Their Lighting Needs
    • 1.2 Calculating The Number Of Grow Lights Needed
      • 1.2.1 1) Determine The Total Square Footage Of The Grow Area
      • 1.2.2 2) Determine The Number Of Lights Needed To Cover The Grow Area
      • 1.2.3 Example
  • 2 How Many Grow Lights You Need: Final Thoughts

 

How Many Grow Lights Do I Need?

Obviously, there is no one-size-fits-all answer here. How many lights you need depends on a number of factors.

You will need to consider the number of plants you have, their size, the growth stages, the light intensity, and the coverage area, in order to ensure that your plants receive the optimal amount of light they need to thrive.

But before anything else, you need to understand the light requirement of your plants. We are going to assume you are growing cannabis, since that is what most visitors to this site grow.

cannabis plants under grow lights

Cannabis is a plant with a high light requirement. This means that everything below also goes for other plants with high light requirements. This includes any fruiting, and most flowering, plants.

 

Cannabis Lighting Requirements

Your cannabis plants have specific lighting requirements that change throughout the different growth stages of cannabis. Understanding these requirements is essential for providing the right amount and type of light for optimal growth.

Giving too much or too little light is a common problem when growing weed and can have a negative effect on your plantsโ€™ health. Here are the key factors to consider.

 

Light Intensity And Spectrum Requirements

The first factor you need to consider is just how much light your plants need. The ideal spectrum for your plants is important as well.

 

Light Intensity

As mentioned, cannabis plants have a high light requirement. But marijuana plants can get too much light, too. They thrive best under a certain range of light intensity.

Generally, weed plants want a light intensity of 600 to 1000 ยตmol/mยฒ/s during the vegetative stage, and a slightly higher intensity of 800 to 1200 ยตmol/mยฒ/s during the flowering stage.

 

Light Spectrum

grow light with different colored diodes

Your plants will also respond differently to various light spectra. During the vegetative stage, a spectrum with higher proportions of blue light promotes leafy growth. In contrast, during the flowering stage, a spectrum with increased red light stimulates flower production.

 

Different Growth Stages And Their Lighting Needs

Plants go through different stages of growth and have different lighting needs during the various stages. We already touched on the two primary stages (vegging and flowering) above. Here is a more complete breakdown.

 

Seedling Stage

During this early phase, cannabis plants require gentle lighting to avoid burning the delicate seedlings. They need an intensity of 100 to 180 ยตmol/mยฒ/s. T5 fluorescent lights or low-intensity LEDs are among the suitable options.

 

Vegetative Stage

In this stage, plants need more intense light to promote healthy leaf growth. Aim for 600 to 1000 ยตmol/mยฒ/s. High-output fluorescent lights or full-spectrum LED grow lights are the more commonly used options.

 

Flowering Stage

As plants transition to the flowering stage, they need even more light. As mentioned above, the ideal range for intensity is between 800 and 1200 ยตmol/mยฒ/s.

Weed plants require a different light spectrum to encourage bud development. High-pressure sodium (HPS) or specific targeted-spectrum LED grow lights with a higher ratio of red light are typically used.

 

Calculating The Number Of Grow Lights Needed

many grow lights in grow space

To determine the number of grow lights you need for your cannabis crop, you need to take several factors into consideration. Here is a step-by-step guide to help you calculate the optimal number of grow lights for your grow space.

 

1) Determine The Total Square Footage Of The Grow Area

  1. Measure the length and width of your grow space.
  2. Multiply the length by the width to obtain the total area in square feet.

 

2) Determine The Number Of Lights Needed To Cover The Grow Area

  1. Check the coverage area of each of your grow lights. You can usually find this information listed in the modelโ€™s specification literature, which should be proved by the manufacturer or is available online.
  2. Divide the total square footage of your grow area (as calculated earlier) by the total coverage area of each grow light, which will give you the number of grow lights needed to cover the entire area.
  3. You will also want to take into account the light drop-off around the outside of the coverage area. The light will be less intense, so you may want to overlap coverage areas. You want the total to add up to a number inside the ideal intensity range for your plants.

 

Example

We will give you a simple example to help illustrate this process. Let’s say you have four plant in a grow tent measuring 4 by 4 feet (or 16 square feet). Each plant takes up a 2 by 2 foot area (4 square feet).

If you have lights that cover a 2 by 2 area (4 square feet), you will need four of them. However, if those light only have the desired intensity in the center, say in a 2 by 1 foot area) and the intensity drops by half in the additional 6 inch space on each side (along the longer side of the light), then the parts of your plants in that area will receive less light.

marijuana under grow lights

The solution is to overlap the outer 6 inches of the coverage area with the same outer 6 inches of the neighboring light. This means you will still have two light next to each other, but you will now have three rows of lights, instead of two. This ensures a more even coverage area.

 

How Many Grow Lights You Need: Final Thoughts

Determining exactly how many grow lights you need depends on a number of factors, like the type of plants you are growing, the growth stages, the grow lights in question, and more.

It seems complicated, but once you know what you are doing, it is actually fairly simple. You just need to figure out the lighting needs of your plants (cannabis was provided above) and the output of your lights (the manufacturer should provide this, but our article on the best LED grow lights also includes this info).

Once you have that, you can figure out how many of the lights it will take to fill your grow area with sufficient light for your plants. Aim for as even a coverage area as you can get. In some cases, it may make sense to buy some smaller, cheaper LED or fluorescent bulbs to fill in areas with less intense coverage.

Reader Interactions

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Primary Sidebar

Recent Articles

thc cbn cbd and marijuana potency

What Are THC, CBN & CBD And How Do They Relate To Marijuana Potency?

Things That Cause Stress In Cannabis Plants

7 Things That Cause Stress In Cannabis Plants (And Why Stress Is Bad)

Improve Bud Quality In Cannabis Plants

6 Ways To Improve Bud Quality In Cannabis Plants

Top 10 Strains For Maximum Yield

Top 10 Cannabis Strains To Grow For Maximum Yield

How To Make Your Own Cannabis-Infused Edibles

How To Make Your Own Cannabis-Infused Edibles At Home (Easy Step-By-Step Guide)

Eco-Friendly Cannabis Cultivation

Eco-Friendly Cannabis Cultivation: 8 Tips For Growing Green And Sustainable

1 Gram Of Weed Per Watt Of Light

1 Gram Of Weed Per Watt Of Light (Is It Realistic & How To Achieve It)

How To Make Cannabis Tinctures At Home

How To Make Cannabis Tinctures At Home (Easy Step-By-Step Guide)

Save Electricity When Growing Weed

7 Tips To Save Electricity When Growing Weed

marijuana flowers

How To Make Bubble Hash At Home (Step-By-Step Beginner’s Guide)

Footer

Important Pages

  • Home
  • About
  • Contact Us
  • Privacy Policy
  • Affiliate Disclosure
  • Terms And Conditions

Image Reuse

Images on this site are free to share (unless attributed to a 3rd party), as long as you give credit to Grow Light Info and provide a link back to the page from which the image came.

Disclaimer

Some recommended products may use affiliate links. GrowLightInfo.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com. As an Amazon Associate I earn from qualifying purchases.

*Amazon and the Amazon logo are trademarks of Amazon.com, Inc, or its affiliates.

Contact

Grow Light Info is owned and operated by:

McBrain Global LLC
30 N Gould Street, Suite R
Sheridan, WY 82801
USA

Phone: +1 (307) 269-0897
Email: mccabesteven9@gmail.com

Copyright © 2025 ยท McBrain Global LLC ยท All rights reserved.