What You Need to Know About Grow Lights?


Grow lights are one of the crucial components to growing indoors since you cannot get enough natural light to sustain and produce flowers. There are three primary kinds of grow lights that growers rely on that provide reliable results for growing cannabis flowers: High Pressure Sodium (HPS), (Ceramic) Metal Halide ((C)MH), and Light Emitting Diodes (LEDs). You can also grow with fluorescent or incandescent but don’t expect great results when growing with cannabis – these bulbs simply do not give off enough useful energy. We’ll talk about the differences between these grow lights and how far to hang them, how high your light intensity should be, and what the spectrum should be for each growth stage.

These days, most growers will opt for purchasing HPS or LED fixtures. CMH/MH fixtures remain a distant third to these two, and perhaps unfairly, because CMH does indeed provide a full enough spectrum for a full growth cycle, but MH bulbs do not – they are great for the veg stage but not for flowering because the spectrum they produce is mainly blue light. CMH does a great job but for our purposes, we’re going to examine just HPS and LED. Let’s take a look at how they compare.

Whether you decide to use HPS or LED or CMH/MH lights, it is up to you. When you do, there are recommendations for light. Let’s take a look at light height according to wattage.

Light Height for HPS/CMH/other HID type lights:

Watts Height (inches)
150w 36” (seedling) / 24” (veg/flower)
250w 36 – 40” (seedling) / 30 – 36” (veg/flower)
400w 48” (seedling) / 36 – 42” (veg/flower)
600w 54” (seedling) / 36 – 42” (veg/flower)
1000w 60” (seedling) / 48 – 54” (veg/flower)


Light height for LEDs:

Growth stage Height (inches)
Seedling 24 – 30”
Veg/flower 18 – 22”


What is the ideal spectrum for each stage of growth?

Great question! We have a handy chart to give you the perfect answer. When purchasing your light, consider the light spectrum and which parts of the spectrum your light emphasizes – that will determine if your light is suitable for the various stages of growth. Our goal is to maximize the production of THC and we can do that by providing different “colors” at different stages of growth.

In this graph, you can see that there are two “points” that are higher than the rest. These peaks show that this coloration of light is more needed for photosynthesis and the creation of chlorophyl and sugars plants utilize to develop. Blue light is utilized by plants to build structure, such as leaves and stems; red light is used to build flowers. This graph is ideal and what you’ll want for your light if you want a full spectrum light. If you want to emphasize either blue or red, look for spectrum charts that do just that.

We hope this has been a useful primer for your growing journey! Good luck and come back for more info!

If you have any questions, please don’t hesitate to reach out to us!

And be sure to check out our other blog posts for useful tips on becoming a great grower!

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