Grow Vegetables Indoors
Sage growing hydroponic under a grow light

Making sense of grow lights

I admit I was completely confused and overwhelmed by grow lights. I didn’t know what all the terms meant and how to choose the best light for my situation. If you want to be an indoor gardener making sense of grow lights in critical.

So let’s cut thru the confusion.

Making sense of grow lights Making sense of grow lights

There are literally thousands of options on the market. I am going to focus on two very common choices. Fluorescent vs LED

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But first let’s get the basics for us non scientists.

making sense of grow lights means understanding Color light waves

All light is made up of color waves. Sunlight or in the case of grow lights “full spectrum” light is all the colors…think rainbow.

Making sense of grow lights Color scale

The blue end is considered cool color. The red end is considered warm color.

So when you see a light offering 3000k or 6000k it does NOT refer to the power of the light as one might think. The k refers to the place the light being emitted falls on the spectrum.

What important to know for plants?

Making sense of grow lights: what your indoor plant really need

Plants use different color lights for different jobs.

Plants use the cooler lights, 4,000 k to 7,000 k grow healthy green leaves.

If you have a house plant or a vegetable that the leaves are most important ie lettuce, greens and non flowering house plants than chooses Cool light range.

Plants use the warmer light color spectrum to flower and grow fruit.

A range on the red, warmer end around 3,000 k is best. Without the warmer color spectrum your vegetables will grow lush without producing any fruit. I speak from experience!

Many grow lights come Full Spectrum. These are great all purpose lights. If you are setting up to grow something specific going more to exactly what your plants need is a better choice.

But what about Nanometers?

Some lighting companies label the spectrum using Nanometers rather than Kelvins. For basic purposes don’t let this get too confusing.

Nanometers is a more specific than Kelvins. It is an exact color spectrum but the same principle applies.

Cool light falls into the 430-450 nanometer range.

Warm light falls between 640 and 680 range.

Color of light is the most important thing to your plants! The rest is all about what works for you.

Making sense of grow lights What kind of light do you need

Watts vs lumens. The basics

Watt is describing the amount of power it takes to run the light. This does not have anything to do with the brightness at all! Many older lights used a lot of watts to run. The newer LED are very efficient and take much fewer watts.

Lumens do describe the brightness of the light. It DOES NOT tell you what color on the spectrum light is.

Don’t get assume that the brighter the light the better!

LED vs Fluorescent

There are hundreds of different sizes and shapes of lights under both of these categories.

Fluorescent bulbs have been around for years. They come in both tube and regular socket style. They can be easy to use and reasonably priced.

The fluorescent light must be put very close to the plant. The height range is from 3″ to 12″ from the plant. After that distance the light loses it effeteness.

LED lights are usually much more energy efficient.

There is also a relatively new product on the market, LED tape. I love this stuff and will do a separate posting on the pro and cons. But for now know that LEDs tend to be more flexible to set up, cheaper to run but often more expensive to purchase.

LED grow lights should be setup between 12″ and 24″ above your plants for best effectiveness.

Not all LED or Fluorescent bulbs are grow lights! Check the color spectrum.

making sense of grow lights: White or blue and red LEDs Which is better?

Making sense of grow lights White or color lights

There have been studies that show proof on both sides of the argument.

I have used both and tried to keep track of which is better. I have honestly never found a difference.

The one thing to keep in mind however is that if you are seed starting or growing things like micro greens, there is no real need for the warmer red light. So if you have a grow light in the cooler spectrum 4,000 k -6,000 k no need to change it.

How much light do my plants need?

There is a general guideline that is good to follow when setting up light for your plants.

Most indoor vegetables need between 8 to 14 hours of light. This is why it might pay off in the long run to buy the most energy efficient lighting.


Don’t make the mistake of thinking more is better. All plants need at least 6 hours of darkness to complete their daily energy processing cycle.

You can kill plants by leaving the lights on 24/7.

Fun fact to leave you with… do you know that plants appear green because green is the only color on the spectrum that they don’t absorb!

If you want to know how to read the label on lighting to make sure you are getting just what you need read Best lighting for indoor gardening

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