The Basic Concepts Of Lighting In Horticulture by Heliospectra


Most of us remember from our high school days that plants are autotrophs. For those of us who were not paying attention back then, it means that plants are capable of creating nutrition such as carbs, proteins, and fats, in order that they might grow.

They create these life-sustaining foods by absorbing specific components from their environment:

  • Nutrients and minerals from the soil
  • Water
  • Carbon Dioxide

Along with temperature, all of these components are of extreme importance for a plant to make its own nutrition, but there is one thing that plants need for all of the other elements to work. 

That essential thing is energy in the form of light. Without the energy that a plant gets from light, the nutrients, minerals, water, and carbon dioxide will not be able to fuel a plants' growth.


Light In Horticulture: Redefining Nature's Potential

Whether you are someone who grows a small amount of crops at home, or you have a massive greenhouse, it is to your advantage to educate yourself about all aspects of your growing production. 

Simply purchasing products, like grow lights, without understanding how plants use light will leave you at a disadvantage. 

Knowing how the process works enables you to make informed decisions about what your plants need and helps you produce the best crops time and time again with success.

In this important ‘By Growers for Growers’ educational series by Heliospectra and presented on YouTube, Johan Lindqvist walks you through the basics of lighting as it applies to plants.

The first in the series is Lesson 1: Basics of Lighting for Horticulture.


What Is Light?

Helio 1


Light is electromagnetic radiation that is in the form of waves that transports energy. There are many different types of electromagnetic radiation. 

There are microwaves, x-rays, gamma rays, and radio waves. Among these types of electromagnetic radiation, there is also light, which is also a type of wave.

Helio 2

Light is a type of particle, a photon that is flowing. Each photon of light has a specific wavelength. Those wavelengths correspond to the color the photon has, and each carries a certain amount of energy.


The Light Spectrum

In order to better understand these photons of light and their individual colors, you need a working knowledge of the light spectrum. 

The light spectrum is a visualization of light. When you look at light, the spectrum tells you how much of that light is blue, green, or red photons. The spectrum is represented on a graph by the wavelength of each color on the X-axis, which allows you to divide the spectrum into segments.

 Helio 3

This division defines blue as the photons with wavelengths between 400nm and 500nm on the spectrum, green is 500nm to 600nm, and red is 600nm to 700nm. 

All yellow light falls under the green spectrum, and orange is in the red spectrum.


The Importance Of The Unit Measurement Of The Y Axis

When looking at a spectrum to measure the light wavelengths on the X-axis, it is essential to have the correct corresponding unit of measurement on the Y-axis. The measurements should be in photons or micromoles (µmo).

Helio 4

If the graph's Y-axis measures in energy (mW) rather than photons (µmo), the results will be skewed concerning plants and be misleading for your purposes.


Photosynthetically Active Radiation (PAR)

This essential type of radiation, photosynthetically active, or PAR, is the type of radiation that stimulates photosynthesis. Plants use this radiation for the photosynthesis process.

 Helio 5

The PAR region comprises all photons with wavelengths between 400nm and 700nm. This range overlaps with the spectrum that is visible to the human eye.

Helio 6


There is another light that is important to plants, too. There are light waves out of the PAR range that is still vital to plants, although not used for photosynthesis. 

Those waves are in the ultraviolet UVA, UVB, and UVC range. Plants use these lightwaves for information on how to grow and what types of compounds to produce.

On the other end of the PAR wavelength is the Far-red (FR), which is between 700nm and 750nm. These wavelengths also send signals to plants. 

Running from 800nm and beyond, the infrared does not have any direct impact on plants. When considering the type of light your plants will need, infrared is much less significant.


Broad Spectrum Light As Used In Horticulture

These two terms, broad-spectrum light and full-spectrum light, are terms that are also used in many fields of science, including horticulture. 

When using those terms regarding horticulture, broad-spectrum is a spectrum with blue, green, and red photons. This spectrum will have all the components of visible light.

If the light spectrum only has blue photons, it is referred to as a narrow band spectrum or a single peak spectrum. A light spectrum that has two colors, as in the example above with blue and red but no green, indicates a dual peak spectrum. Neither of those would be referred to as a broad spectrum.


Full Spectrum Light As Used In Horticulture 

Full spectrum light is similar to a broad spectrum in that it also has blue, green, and red photons. However, there is a significant difference between broad and full spectrum.


In full spectrum, the wavelengths will also include UV and FR. A full spectrum will have all of the elements of light that are relevant to plants.


The difference between broad-spectrum light and full spectrum light is evidenced in the chart above, making this vital difference easily understood.

In Conclusion

Using the United States as an example, one quick glance at the maps below will give you a very clear idea of how challenging it can be to depend on the environment to have the correct light to grow crops of any kind. Daily Light Integral (DLI) is the light intensity and duration of PAR received each day. The accumulated light a plant receives is correlated to plant quality and yield. If you are an individual who is growing for their family or if you are developing a small business, it can be daunting to depend on the outdoor elements for those critical needs.


Maps showing outdoor DLI by month

Using LED grow lights for your crops enables you to control and regulate the light levels to the precise requirements of your plants. LED lights and a control system such as helioCORE™ will allow you to create your own individual lighting strategies.

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  • Ma. Elena
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