A bright idea: lighting for indoor nurseries

Sunshine or snack?

Imagine, you are sitting outside on a clear and sunny afternoon. You feel the warmth of the sun shining down on your face. For you, it’s a pleasant reminder to apply sunscreen. For the surrounding plants, it’s lunchtime!

Plants, as you are probably aware, require light to survive. Photosynthesis is a process in which light, water, and carbon dioxide are transformed into oxygen and energy by plants. It is a chemical reaction where captured light is turned into sugar (carbohydrates). Plants use this sugar as a form of energy to grow, develop, and produce seeds.

Plants have traditionally acquired all light from the sun. Today, however, all types of plants, from beautiful houseplants to large-scale agricultural crops, are cultivated indoors. In each scenario, proper artificial lighting is required to stimulate plant development. But what kind of light do plants require, and how much is sufficient?

Let there be light

Plants require light to grow, but this light does not have to come from the sun. Grow lights are artificial lights that are used to enable plants to photosynthesize indoors. The essential variables for determining the appropriate usage of grow lights for your indoor plants are the type, duration, and intensity of light.

What type of light should you use?

Did you know that visible light has different colors? The color of visible light is determined by its wavelength. When we talk about the wavelength of light, we mean the distance between two consecutive crests (the highest points) or troughs (the lowest points) of the light wave. These wavelengths are measured in nanometres (nm), units so small that there are 1,000,000 of them in 1 millimetre!

“Why is this important?”, I hear you ask. Well, when it comes to photosynthesis, plants prefer wavelengths within the blue range (400-500 nm) and the red range (600-700 nm). Plants need blue light to grow strong stems and make chlorophyll, the pigment responsible for absorbing light. Blue light limits extension growth, making plants shorter and thicker with darker leaves. Red light is necessary in order for plants to flower or produce fruit, however, giving your plants too much red light can lead to elongated and weak stems.

Here enters the LED grow lights, the increasingly preferred option for controlled environments. LED grow lights are very energy-efficient and relatively cheap, with the ability to generate specific wavelengths. This means that you can give your plants the ideal wavelengths for each stage of their development.

Another advantage of LED grow lights is that they do not produce as much heat as incandescent lighting, saving growers in costs associated with cooling systems.

Incandescent lighting, like sunshine, provides the whole range of wavelengths, which may seem advantageous. Unfortunately, this spectrum also contains Ultraviolet-B (UVB) radiation, which can harm your plants. Another advantage of LED grow lights is that they often do not emit UVB - one less thing to worry about.

When should you leave your grow lights on?

The number of hours that plants are exposed to light each day is known as the day length or photoperiod. In nature, the photoperiod changes with the seasons. Plants respond to these changes in photoperiod to adapt to the seasonal changes in their environment. For this reason, some plants need more daylight hours than others and these needs vary with the plants’ stage of development. The best example of this is in flowering plants.

Some plants flower when they are exposed to day lengths of less than 12 hours (short-day plants) while others flower in response to day lengths of more than 12 hours (long-day plants). Then there are also plants that flowers regardless of the amount of light they received (day-neutral plant plants), so be sure to check the photoperiod requirements of your plants before setting up your nurseries.

The advantage of using grow lights is that you can control the photoperiod to prevent or encourage flowering and customize the day length to suit the needs of the plants you are cultivating.

How much light is enough?

The intensity or amount of visible light generated by a certain source is measured in lux. Plants have variable light intensity needs depending on where they are in the plant development cycle. Seedlings prefer lower light intensities, but vegetative and blooming plants require greater light intensities.

When there is adequate water, carbon dioxide, and an acceptable temperature, increasing the intensity of light leads to an increase in the rate of photosynthesis. Photosynthesis will be delayed if your plants do not receive enough light. Spindly stems, tiny, light leaves, and brown leaf tips might result from this.

Conversely, if the light intensity is too high it can damage the chlorophyll in your plants, resulting in a decrease in the rate of photosynthesis and even plant death. To ensure that your plants are receiving the ideal amount of light, you can measure the strength of your grow lights using a photometer and compare this to the recommended range (in lux) for your plants at each stage of development.

The future is bright

Light is required for plants to create the energy they require to grow. Indoor gardening using artificial lighting gives us the ability to control the type and amount of light that our plants get. To keep our indoor plants happy and healthy, we made our own sun. What a light-bulb moment.

For more interesting articles diving into the fascinating sphere of plant science, keep checking this space!

By Laura Steel | 20 September 2022

Laura is a Melbourne-based writer and science communicator with 4 years of experience working for an Australian medicinal cannabis company. She completed a bachelor’s degree with Honours in Biological Sciences at Monash University and is currently undertaking a PhD in plant developmental and reproductive biology with La Trobe University and the ARC Research Hub for Medicinal Agriculture.

References

  • Barber, J., & Andersson, B. (1992). Too much of a good thing: light can be bad for photosynthesis. Trends Biochem Sci, 17(2), 61-66. doi:10.1016/0968-0004(92)90503-2
  • Fan, X.-X., Xu, Z.-G., Liu, X.-Y., Tang, C.-M., Wang, L.-W., & Han, X.-l. (2013). Effects of light intensity on the growth and leaf development of young tomato plants grown under a combination of red and blue light. Scientia Horticulturae, 153, 50-55. doi:https://doi.org/10.1016/j.scienta.2013.01.017
  • Rezazadeh, A., Harkess, R. L., & Telmadarrehei, T. (2018). The Effect of Light Intensity and Temperature on Flowering and Morphology of Potted Red Firespike. Horticulturae, 4(4), 36. Retrieved from https://www.mdpi.com/2311-7524/4/4/36
  • Runkle, E. (2017). Effects of blue light on plants. Michigan State University Extension: Floriculture Team. Retrieved from http://www. flor. hrt. msu. edu/assets/Uploads/Blue-light. pdf.