Lighting your indoor garden

Lighting is a key component for a successful indoor garden. Most tutorials go into depth on HID, low-pressure sodium lights, T5s, and several others.

We’ve decided to forgo the global overview to focus on LEDs – our favorite for function and price.

Indoor Garden Lighting Basics

A quick overview on lights in plants: Plants don’t handle lights like our eyes do; they only respond to certain wavelengths (colors), mostly in the red and blue ranges. We recommend watching Farmer Tyler’s playlist on plant lights for a deep dive into how lighting works.

The short version is:

Red is where the growth and most of the plant’s energy come from. Plants grown with lots of red have more mass but might sprawl if you give them too much
Green is not taken in by the plants very well
Blue dictates how much the plant’s internal processes perceive the light as bright. More blue makes plants grow compact.
Deep red is used as a trigger in certain chemical processes, the most obvious of one it the mechanism that makes the plant grow taller
UVA affects color. UVB can enhance terpene production. UVC kills surface bacteria. Too much of any UV range will hurt your plant.

How to Measure Lighting for Indoor Gardening

Because plants interact with light differently than humans, we can’t go by the usual measure of light intensity (Lumens, or Lux). For your garden, the Photosynthetically Active Radiation (PAR) is what we are actually after.

PAR measures the amount of light in the range of frequencies that chlorophyll actually responds to. PAR is generally measure in μmol/m2/sec. Most crops that farmers would work on have a measured amount of light they need per day called the Day Light Index (DLI), which is a measure of the amount of photons you get in a square meter per day. You can convert the instantaneous PAR reading to DLI by multiplying your PAR output by the number of hours your lights are on per day by 0.0864 and then divding by 24.

In general, you need a light that runs for a long time without failures, and puts out enough PAR for your crop.

Our general rule: 500μmol/m2/sec is the middle ground for most flowering plants and 250μmol/m2/sec for leafy plants. This is a very general rule of thumb, of course. Shade plants need less, and most medicinal herbs need upwards of 750μmol/m2/sec.

Practically speaking you need about 30W-40W of LED lighting (actual wall draw) per square foot or 350W-425W per square meter to get to that point.

Our recommendations:

- Roleadro 300W LED Grow Light 2nd Generation – Good for a 2’x2′ space flowering, and very inexpensive while still having great output. I use this light for my flowering plants.
- Roleadro 2nd Generation 600W LED Plant Grow Light – For a 3’x3′ space flowering, it’s the larger brother to the one above.
- Horticulture Lighting Group USA HLG 135 – This super-efficient board uses some of the best in LED tech. Great coverage, reliability, and customer service. 2’x2′
- HLG 550 V2 LED Grow Light – Sure, it’s expensive, but it will efficiently do a 4’x4′ tent and uses the most efficient LEDs currently available. 510W