Grow Light Basics

I don't think I ever worked harder to write a blog post. The science of grow lights is far more complex than grow light vendors will have you believe. I hope I can provide the basics so you can buy the right lights for your situation.

First, assess your needs. 

  • How many plants do you need to light?
  • How long will you need a germination station? A few weeks, a few months, or all year?
  • Will you grow seedlings into full size plants? (I plan to do this with lettuce.)

All these questions matter because it will dictate what type of light (color) you need and how close the light must be to your plants. 

Two Words To Know: Kelvin and Lumen

You'll see these words a lot when discussing grow lights so let me define them in simplest form.

Kelvin is the color temperature of light. It ranges from candlelight which is 1000 Kelvin all the way to blue sky which reaches 10,000 Kelvin.

Lumen is the intensity of light. That's how bright your bulbs are.

Your goal is to recreate light for your seedlings to mimic light at around midday direct sun which ranges between 5000-7000 Kelvin.

What type of light do you need?

This is where it gets complicated. You have to factor in everything from what stage your seedlings are in to how close you should place your lights. This again depends on the intensity and color of your bulbs.

Sorry to say, vendors don't make it easy for you to make those decisions.

My best advice to you is to select a bulb or diode that represents full spectrum light. Here again vendors can be misleading and claim full spectrum light even though they only use red and blue light diodes (called blurple).

Look at their color charts. You'll want red, blue and white light diodes if you use the integrated LED grow lights. By the way, "integrated" means you throw the entire fixture away once it goes out. You can't replace the diodes. They do last a very long time though. The ones I bought are supposed to last 50,000 hours.

If you use fluorescent bulbs, (which I quite like) they are less cost effective, but you can replace the bulbs to the color (Kelvin) your plants need as they grow.

For most average gardeners you're probably safer with diodes. Just make sure it's full spectrum.




If I could afford it, I would buy the Mars Hydro Grow Light. It has everything you need to grow from seedlings to full plants, including a timer and dimmer knob. I am leaving it on my Wish List because I think it would be great to have for the plants/trees I bring in to overwinter in my atrium.

A Good Contender for advanced gardeners:


I really like this one. It's large and covers a big footprint of plants. The nice thing about this is that it has replaceable fluorescent bulbs depending on what Kelvin you need for your plants. The cons are is that you will have to select the correct color for the stage of plants you're growing. Good for experienced gardeners with mass plantings--everything from marijuana to African violets. Not so convenient for the hobby gardener.

Overall Good Choices for the hobby gardener:



Other Grow Light Facts:

Plants needs blue wavelengths for photosynthesis and plant growth. Red wavelengths promote vegetative growth and flowering. White light provides all wavelengths.

Lights should stay on 14-16 hours a day. Grow lights should be 6-24 inches from seedlings. If you use fluorescent bulbs your distance should be up to 30 inches since it gives off much more heat.

You'll know if your distance is off if your plants look burned or stressed. 

If they're spindly you have too much red light. If the plants are stunted you have too much blue light. That's why it's important to include white light in your grow lights. Balance.

Lumens as mentioned earlier is the intensity of light. I've seen all sorts of wild numbers thrown out but this seemed the most reliable source. They suggest between 300-800 lumens per square foot.


There are hundreds of brands and types to choose from. It took me weeks to select the one I finally bought. In the end, because I was going to use them primarily to start my seedlings, I opted for one that gave me full spectrum light at 48 inch width to cover an entire shelf of plants.

Don't settle for the cheapest. You won't do your plants any favors if you get chintzy. Go over the descriptions of the various lights in your price range. Go for one that gives you the best range in lumens and Kelvin. Remember, your goal is to mimic sunlight. 

Sunlight is full spectrum which includes infrared and green. Most brands ignore those two wavelengths, but recent studies show that plants need them just as much as red, blue, and white lights. It only makes sense since this is exactly what real sunlight provides.

I hope I broke down the basics into understandable parts. I didn't want to overwhelm you with too much information, but I did want to warn you that vendors sometimes leave out important information.

Grow lights are great, especially if you want a head start on planting. I think it's a game changer for me.

Next time, I'll go through the steps I took to create my 'indoor greenhouse'. And I'll post updates as time goes by to show you my grow light progress. I should've been much further along in planting, but a combination of severe weather and a huge demand for growing supplies set me back weeks.

At first, the lights and even my shelving unit were back-ordered, but worse, even when I got my order in I couldn't get them delivered. They were in post office limbo wandering the country for two more weeks. It was crazy!

It set me back by nearly six weeks, time that could've been spent growing seedlings. Garden One is ready and I should have Garden Two prepped by today. I've got a few seedlings I can put out there, but for now I'll concentrate on fast growing veggies like radishes, greens, and snow peas.

It's off to the races for gardening. If you want to get a head start on planting, or live in a cooler, wetter area, or a shorter growing season, try a grow light to put you ahead of the game. You won't regret it.

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Anonymous said…
I definitely bought the cheap blurple lights without the white wavelength and can attest that they are a waste of money. (Facepalm).

Lights make a difference! I just started some seeds by a warm window, we’ll see how they do.

Maria Zannini said…
And that's what frustrates me. Sellers sing the praises of blurple without understanding the science of plant stages. They need white light which includes infrared and green wavelengths.

I do plan to get the Mars Hydro grow light later this year for my bigger plants that are flowering and producing during the fall.

The one I bought has white lights but could use more. It's enough for now.