It’s that time of year again–the snow will surely move in sooner rather than later and gardeners will be stuck inside.  While indoor growing space is often far more limited than outdoor space, there are still plenty of ways to continue gardening inside throughout the winter with the help of grow lights!  A grow light is one of the most exciting purchases a gardener can make.  Indoor grow lights can be used as a 100% replacement for the sun or as a supplemental light source to a window/greenhouse and as daylight extension in the short Montana winter days.  There are several different types of indoor grow lights and choosing the right one for you and your applications will be important for your success. 


The Basics:

Understanding a few basic concepts such a spectrum, intensity and footprint will help you to make an informed decision when purchasing a grow light.  


Lighting spectrum refers to the different wavelengths of light (measured in nanometers) that our eyes can see–or not see.  The portion of light wavelengths that is most important to plants lies between 400-700 nm and is called the ‘Photosynthetically Active Radiation’ or PAR.  Light in the 400-500 nm range is referred to as ‘blue’ and is ideal for seed starting, cloning, vegetative growth (i.e. basil, lettuce, other things that do not need to flower) and houseplant care whereas the spectrum between 580 nm- 700 nm is referred to as ‘red’ and is ideal for flowering and fruiting.  

You may also see spectrum stated in ‘Kelvin’ or ‘K.’  This unit refers to the light source’s warmth or coolness.  A Kelvin value of 2,500 is called warm and falls in the ‘red’ or flowering category and is the most common Kelvin value in grow lights for flowering.  A Kelvin value of 6,500 is called cool and falls in the ‘blue’ or vegetative category and is the most common kelvin value in grow lights for vegetative growth.


The amount of PAR needs to be sufficient to ‘power’ your plants.  Different types of grow lights produce different intensities of light.  Generally, the higher the number of watts, the more intense the light will be.  Additionally, the distance from the plant to the light source can affect intensity.  The farther away the light source the lesser intensity.  Always keep your plants at the appropriate distance away from the light source for optimal growth.  

  • If your light source is too far away from the plant or too low of an intensity, it will begin stretching.  A stretched plant may be referred to as ‘leggy’ and will have a long, weak stem with few leaves.  
  • If your light source is too close to your plant or is too intense, leaves may become burned or bleached.  


The footprint refers to the square footage that the grow light will cover.  If you hang your grow light higher, its footprint will increase but its intensity will decrease. 


Three Main Types of Grow Lights:

  • T5 Fluorescent 
      1. T5’s are a very versatile option and work well for a wide range of applications.  Not to mention, they are very cost effective.  They produce less heat and are less intense than HID lighting options making them ideal for houseplants, seed starting, seedlings, clones, micro-greens and other low to medium light plants.  T5’s are most commonly found in 2ft and 4ft lengths with bulbs ranging from 24-54 watts per bulb.  Fixtures can have between 1-8 bulbs.  Look for vegetative bulbs with a ‘blue’ spectrum.  
  • High Intensity Discharge (HID)
      1. As their names imply, these lights have high intensity.  HID’s are typically found in wattages ranging from 315 watts- 1,000 watts.  HID lamps require a ballast to power the bulb and often have a ‘hood’ to help disperse the light.  Always make sure that your ballast and bulb are the same wattage! There are two main types of HID lamps: high pressure sodium (HPS) and metal halide (MH).  Metal Halide lamps are in the blue spectrum and used for the vegetative stage of plant growth.  High Pressure Sodium lamps are in the red spectrum and used for the flowering and fruiting stage of plant growth.
  • Light Emitting Diode (LED)
    1. LED’s are a popular choice for many gardeners who are willing to pay a little bit more up front.  LED’s tend to use less power for an equivalent intensity compared to their T5 and HID counterparts.  Oftentimes, LED’s are considered full spectrum and can be used for seeds, vegetative plants and flowering plants.  LED grow lights can range from 24 watts to 1500 watts.  Benefits of  LEDs include:
      • Less heat than HID’s (and usually less than T5’s)
      • No changing of bulbs
      • No mercury content in diodes
      • Less power usage for more intensity

Which grow light is best for your application? Stop by 111 S Broadway in Belgrade, MT to view options of T5’s, HID’s and LED’s!

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