Simple Guide To Indoor Grow Light Spectrum & Color Temperature

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Choosing the correct light spectrum is one of the 3 main basics of plant lighting. Sunlight and various other types of light that we see is actually made up of several different colors. For indoor gardens, it’s important to provide the proper spectrum during the right stage for best growth.

Don’t worry, I’m all about hydroponic gardening made EASY, so we will keep things simple.

The Light Spectrum Is For the Pigments

Plants use energy from light for the process of photosynthesis. In order to absorb the light, plants contain pigments, molecules that absorb specific wavelengths of light and reflect all others (that reflected light is the color that you see).

There are several pigments involved in photosynthesis. Chlorophyll (a)  and carotenoids are the main ones so we will just discuss those to keep it simple.

Chlorophyll (a)

Chlorophyll a is the most abundant pigment found in plants. They do not take in very much green light, reflecting it away from the plant. This is why plants appear green.

Chlorophyll a plays an important role in photosynthesis, allowing plants to absorb light energy to be turned into plant energy.

 

Carotenoid

Carotenoids are the second most prominent pigment found in plants. They are responsible for the yellow, orange or red colors we see in plants and fruit. It is what we see in the leaves as they change colors in the fall, as the chlorophyll is less abundant.

They assist in the absorption of light, then transfer the energy to the chlorophyll. They also protect chlorophyll from photodamage.

What Light Spectrums Do Plants Need?

Plants some blue light and red light for growth but need other light spectrums as well for great all-around growth.

LED Lighting 

LED’s are considered efficient for several reasons. One of which is that they can be customized to provide the exact colors that plants need leaving out the colors they don’t.

For the best all-around growing conditions for all parts of a plants life cycle LED lighting should contain some:

  • Red LEDs (600-700 nm)
  • Blue LEDs(400-500 nm)
  • Some Green LEDs (500-600 nm)
  • Some Far-Red LEDs (700-800 nm)
  • Some White LEDs
  • Some IR, UV LEDs

There are many LED grow lights are configured with the proper spectrum for all stages of growth, meaning you can use the same light for the whole grow.

Traditional Grow Lights

When I say traditional grow lights I’m pretty much talking about everything not LED. This includes fluorescent, HID, and CFL lighting.

These lights do not emit the single colors that LED lights do. When looking at the light emitted by a typical glow light we usually see either a bright daylight or a soft yellowish hue.

Typical grow lights is measured by color temperature in the measurement of “Kelvin”. Below you can see the Kelvin scale.

At the lower end of the scale, the red spectrum of light, is the soft hue. At the other end of the scale, you have more of the blue spectrum of light, the daylight hue.

In addition to the red and blue spectrums, even though we can’t see it, there are the other color spectrums being given off by these lights as well.

What’s The Best Light  For Seedlings?

Plants in the seedling stage need more light from the blue spectrum. For traditional lighting, you’re going to want daylight bulbs at the higher end of the Kelvin scale.

You should use bulbs that are in the 5,000 Kelvin range and up for your seedlings.

What’s The Best Light  Vegetative Growth?

The same lighting that works best for seedling also works well for vegetative growth. Plants in the vegetative stage need blue light, at the higher end of the Kelvin scale.

This light is high energy, promoting fast growth in leaves, but too much and it can actually slow growth.

You should use more bulbs that are in the 5,000-7,500 Kelvin range and up for plants in the vegetative stage.

What’s The Best Light  For Flowering and Fruiting Stages?

As your plant enters into the flowing and fruiting stages of its life cycle it will need more of the red spectrum of light. This is the lighting that is on the lower end of the Kelvin scale.

This light is low energy, promoting flowering, blooming and fruiting. Not enough in red light at this stage in growth will affect these processes.

You should use more bulbs that are in the 2,000-3,000 Kelvin range for plants in the flowering/fruiting vegetative stages.

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2 Answers

  1. Rhonda Williamson
    October 13, 2018 at 9:55 pm

    Your explanations are very concise and easy to understand, thank you.

    I was hoping to find a one-size-fits-all answer for what color light to use thru all stages. I don’t need seedling lights, so just blue for vegetation and red for flowering.

    I’ve read that white lights don’t provide a wide enough spectrum, but now you said that that there are other colors in white light that my plants need.

    Please help! Should I use red/blue OR white LEDs?

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