What Is Light Spectrum?

The light spectrum is the range of waves within the electromagnetic spectrum that is visible to us as human beings. Measured in nanometres (nm), the visible spectrum sits in between 380nm to 750nm on the scale. This means the blue end (bottom) of the visible spectrum has a slightly shorter wavelength than the red side (top).

The sun emits solar energy, of which a really small portion winds up reaching Earth. This is because the ozone layer absorbs and reflects back most of the harmful waves, enabling life to flourish. Waves that infiltrate the ozone layer are in between 300nm - 1100nm, so the spectrum coming into the atmosphere is wider than we have the ability to see.

Beyond the visible light spectrum we have gamma waves, x rays, ultraviolet waves, infrared, microwaves and radio waves. Ultraviolet waves and infrared waves sit at either end of the visible spectrum meaning they are included in the wavelengths that pass through the ozone. Both are beneficial for plants in some ways.

• UVC (180 - 280nm) - Includes damaging ultraviolet waves that are blocked by the ozone layer. Causes serious burns.
• UVB (280 - 315nm) - Can burn skin however only small amounts reach earth. Higher altitude areas will have higher levels of UVB.
• UVA (315 - 400nm) - Always present in the atmosphere but not visible. 95% of ultraviolet waves entering through the ozone are UVA.
• Visible Light (380 - 750nm) - The range of the electromagnetic spectrum that we are able to see as color.
• Infrared (700 - 1100nm) - Invisible to the human eye but can be felt as heat.

Why Light Spectrum Is Necessary

Cannabis plants need the right kind of light to grow to their full potential. Without the right spectrums of light, plants can underperform, growing small and generating low yields. Fortunately, indoor growing techniques have enabled us to simulate the most vital aspects of the sunlight received by plants outdoors.

Outdoor plants get the full spectrum of light supplied by the sun. In the spring, the spectrum of light that filters through the atmosphere results in a bluish tint. The blue spectra is what allows plants to develop strong foliage during the early stages of growth.

As the summer hits, the sun is higher in the sky and more light passes through the atmosphere. By the time fall comes the sun starts to dip, when the red spectra is most prominent. Red wavelengths indicate the end of summer so plants grow flowers in an attempt to pollinate before winter.

How Marijuana Plants React to Light

Cannabis plants can flourish well under blue and red lights provided they receive the right spectra within the color band. By singling out these wavelengths, plants have better access to the kind of light they need. This is among the reasons why indoor plants can be grown smaller than outdoor plants, since they do not have to stretch in search for the necessary spectra.

• Blue (400 - 500nm) - Blue light is required for plants to grow strong leaves and branches throughout its vegetative cycle. Offering high quantities of blue leads to short, bushy plants, which can be helpful for growers trying to prevent tall plants with long branches. Suggested for seedlings, especially if you are growing indoors.
• Red/Infrared (620 - 750nm) - Red is essential for expanding plant structure and promoting bud production. Naturally, plants use red light to recognise when it is day or night. Small amounts of infrared make its way through the atmosphere during sunrise and sunset when wavelengths are longer. Marijuana plants grow taller under infrared until visible red becomes more direct.

Photoreceptors in a cannabis plant's leaves are continuously working to understand the light spectrum surrounding them. Leaves will turn to face the light during the day. When there is no light cannabis plants preserve their energy by 'relaxing' their leaves, making them sag slightly. Photoreceptors do not actually convert light into energy, which is more to do with photosynthesis.

How a marijuana plant reacts to light will also depend on the strain and where it stems from. Some genetics have been brought from high elevation areas where the light is more powerful and there is a higher presence of UVB rays. It has been argued that exposure to more UVB can boost THC production, although this theory is inconclusive and needs to be researched more.

Best Spectrum to Grow Cannabis

It is difficult to say exactly which part of the color spectrum is best but a large part of it has to do with the kind of light your marijuana plants are grown under. Not all lights produce the same spectrum so choosing will depend on the outcomes you are trying to achieve. The main thing is that your garden gets enough blue light throughout the vegetative cycle and sufficient red light for flowering.

You might be intending to grow indoors where you can have complete control over the light. Or perhaps you're considering trying some outdoor plants, a lot of which will be determined by the sun. Whichever you pick, make sure your plants get plenty of light.

• CFL (compact fluorescent light) lights are normally measured in Kelvin (K), which informs us the color temperature of a bulb. Cooler, blueish lights have a higher Kelvin reading (6000 - 6400k), whereas a CFL that looks red will have a lower reading (2800k).
• LED (light emitting diode) - LEDs produce a narrow spectrum of light, either in a small band of blue or red. Red, blue and white LEDs are often blended to create a 'full spectrum' emission that plants can understand for proper growth.
• HPS (high pressure sodium) - Yellow/red light can be used throughout the grow cycle, but plants will grow taller with more spacing between internodes. Cannabis plants benefit from HPS lighting primarily in the flowering stage.

If you are growing outdoors, you can anticipate plants to get larger than they would indoors since the spectrum is wider. Depending on where you live and the time of year, plants will react to the light in different ways.

The color spectrum of your grow light is necessary but if you want to produce good yields, the intensity is also necessary. The intensity of your light source plays a big role in plant growth and has to be powerful enough for plants to photosynthesise correctly. If cannabis plants do not receive enough light, it doesn't matter what spectrum they get, because they will not have the ability to function.

For all the grow lighting supplies with the best and latest technology, contact Grower’s Choice at 909-972-8419 or visit our website at Growersc.com for more information.