How Light Colour Affects Plant Growth

The beauty of growing your own plants is the ability to control their environment, every factor contributing to their growth, from the type of soil to the quality of water.

There's a common question we get asked every week and that is "How does light colour affect plant growth?"

Well, there's a long answer and a short answer to that question and for those who just want the latter then you can check out the below chart and go on with your day. For those who want to learn a little more, continue reading as we will go in to each one. 

What Colour Light is Best For Growing Plants?

Alot of growers use specific colour temperatures for certain stages of plant growth to get optimum results. If we had to recommened the best all round colour temperature for plants then it would have to be around 3500k. 


3500K still has a decent amount of blue(which is good for stem and leaf growth) but also has a good amount of red(which is good for flowering & fruiting). 

Understanding Light Colour and Kelvin

Before we delve into the nitty-gritty, let's clarify a couple of terms.
What do we mean when we say light colour, also known as colour temperature?

Colour temperature is measured in units called Kelvin (K). The Kelvin scale ranges from 1500K (warm colours like reds and oranges) to 8000K (cool colours like deep blues).

Now you may be thinking, "But, plants are green! Don't they need green light?"
Well, actually, plants are green because they reflect green light, not absorb it. They prefer to soak up light at the opposite ends of the spectrum - the blues and reds. And these colours, as it turns out, influence different aspects of a plant's growth.

Deep Blue (5000K - 8000K) 

At the highest end of the spectrum, we have deep blue light. This cool colour encourages the best leaf and stem growth. It's like a boost for the plant's overall structure, promoting sturdy, well-developed leaves and stems. This is particularly helpful during the vegetative stage of the plant's lifecycle when it's focusing on growing out rather than up.

Above is 6000K par spectrum graph. You will notice high ammounts of blue.

In addition, deep blue light leads to more compact internodes. This is closely linked with the production of chlorophyll within plants. When plants are exposed to an ample amount of blue light, they respond by growing healthy, sturdy stems and leaves.

Light Blue (4000K - 5000K)

Next, we have light blue. This colour still encourages good leaf and stem growth, but not as intensely as deep blue. It's a bit like the younger sibling of deep blue - still effective, but not quite as potent.

Neutral White (4000K)

Neutral white light promotes normal growth. It provides a balanced mix of all light colours, ensuring the plant gets a little bit of everything it needs.

Above is 4000K par spectrum graph. You will similar intensities in the amount of blue and red.

Warm Neutral (3700K - 4000K)

As we move towards the warmer end of the spectrum, we meet warm neutral light. This promotes rapid growth in plants. It's like a general motivator, pushing the plant to grow faster and stronger.

Warmer Yellow (3000K - 3700K)

Warmer yellow light promotes high active photosynthesis for all stages of plant growth. Photosynthesis, as you might remember from school, is the process by which plants convert light energy into chemical energy - in other words, it's how they eat.

 

The 3500K still has a nice amount of blue(which is good for stem and leaf growth) but also has a good amount of red(which is good for flowering & fruiting). 

 

Hot Orange or Red (1500K - 3000K)

Finally, at the warmest end of the spectrum, we have hot orange or red light. This light promotes flowering in plants. It's like a love song for plants, encouraging them to produce those beautiful blossoms and fruits we all admire.

The above is a 2700k spectrum graph. You will notice a nice amount of red which is best for flowering/fruiting stage.

So, there you have it - a handy guide to the impact of light colour on plant growth.
While it might seem like a small detail, the colour of the light your plants receive can have a significant effect on their development. Whether you're trying to grow a leafy fern, a sturdy oak, or a blooming orchid, knowing how to control light colour can give your green thumb a serious boost.

Happy growing, folks!