Now that you have a basic understanding of indoor grow lights, let’s dive into how to choose one for your indoor gardening space.  First, calculate the square footage of your growing space.  To calculate square footage, measure the length of the space and the width of the space.  Multiply them together for your total square footage.

Length of Growing Space(feet) x Width of Growing Space (feet)= Square footage

Next, determine the types of plants that you would like to grow.  A crop like lettuce requires medium light while crops like tomatoes or peppers requires high light levels. As a rule of thumb, if the crop you are growing is a full sun crop, it requires high light levels.  If the crop you are growing is shade to partial sun, it is a low to medium light crop.

  • For low to medium light crops, 25-30 watts per square foot is necessary.  
  • For high light crops, 40 watts per square foot is necessary.  


Let’s say you’re gardening in a 2 ft x 4 ft space and want to grow lettuce.  You know that you have 8 square feet of growing space (2ft x 4ft = 8 sq ft) and need approximately 30 watts of light per square foot.

8 square feet x 30 watts = 240 watts

You will want to seek out a fixture that has the capability to run at 240 watts if you are choosing a T5 or HID fixture.  


LED fixtures are more efficient than HID and T5 fixtures, requiring less wattage per square foot.  

  • For low to medium light plants, look for an LED that is 20-25 watts per square foot.  
  • For high light plants, look for LED fixtures that can provide 32 watts per square foot.  

From the example above, if you are growing lettuce in an 8 square foot space:

8 square feet x 25 watts= 200 watt LED Fixture


A few things to keep in mind:

  • Starting seeds requires less light.  If your only aim is to start seeds inside in the spring, you do not need the full wattage that the mature plant will need.  
  • If your gardening space is by a window that receives a lot of sunlight, you may not need the full calculated wattage.  
  • Microgreens and most house plants require even less light than low light crops.

Looking for more information or want to view options? Stop by 111 S Broadway in Belgrade, MT for all of your indoor gardening needs.

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