Light Planning: 3 Steps to Ensure Efficient Plant Growth with LEDS
Acquiring LED grow lights is an investment that is bound to pay off over time due to the lights’ low energy consumption, low heat emission and light spectra optimized for efficient plant growth. However, the investment may prove to be wasteful if the crucial step of light planning is executed improperly. It is all about achieving the largest possible optimal light intensity area with lowest possible number of luminaires.
Step 1: Determining plant requirements
Through the process of light planning we determine how best to feed plants with light. Before we do that, we need to understand the plant in question and its needs:
- Daily photoperiod, number of hours we expose the plant to light within a 24 hour period
- Intensity of lighting, how many photons are ‘fed’ to the plants, typically measured in µmol/m2/s
- Determining the right light spectrum, i.e. combinations of wavelengths, for each growth phase
What makes this task challenging are different requirements for each plant variety as well as each growth phase. Good artificial lighting is a close match to sunlight, but artificial lighting can go even a step further and feed the plants with wavelengths that could grow plants even faster and more nutrient dense than when grown under sunlight. The know-how of how plants respond to light comes from years of research and data accumulation on plants and spectra varieties and their perfect matches. For instance, a lettuce plant needs ~80 µmol/m2/s during seedling, ~150 µmol/m2/s during vegetative phase and above 200 µmol/m2/s when it starts to flower. The understanding of its light level need is derived from multiple experiments where its behavior was observed under different types of light sources and intensity levels.
Figure 1 – Lettuce plants grown under different light intensity levels of a single LED grow light spectrum. Light intensity at each growth phase plays an important role when highest possible biomass together with premium quality is desired. The decision on the micromole level to which the plant will be exposed should be based on customers’ needs. These needs include compact or elongated plants, high number of leaves, delayed or accelerated flowering etc.
Step 2: The choice of luminaires
Understanding how much light a plant needs in each of its growth phases gives input to how many luminaires should be used, what kind of luminaires and how they should be positioned. Simultaneously, the application determines the type of luminaires to be used. Applications range from very low light intensity installations, such as tissue culture laboratories where the intensities range from 10 to 100 µmol/m2/s to high light intensity installations, such as a growth chamber mimicking outdoor conditions where light intensity could be as high as 2000 µmol/m2/s. Greenhouse-grown plants could fall anywhere in between those micromole levels, depending on the crop cultivated.
Figure 2 – Typically LED grow lights come in three shapes: tubes, bars and box lights. Tubes are low intensity, negligible heat luminaires often used as retrofit for T8 fluorescent tubes. Tissue culture and vertical farming are the most common applications. Bars vary in intensity greatly and are thus most versatile, ranging in applications from multi-tier cultivation to greenhouses where they hang high and cover a large area of crop. Box lights are typically high intensity lights and are thus used in greenhouses, sometimes as HID replacements.
When all parameters mentioned above have been determined, the process of light planning can start. Using a software application such as Dialux we should create a plan that fulfills the goals of light planning.
Step 3: Light planning
The goals of light planning:
- To meet the µmol/m2/s requirements for each growth phase with the lowest possible fixture number –thus helping to cut costs of the lighting system acquisition.
- To achieve the maximum light uniformity of the illuminated area. This means creating the most efficient lighting layout with which the biggest amount of crops will be covered with the required light intensity levels. This decision helps to get the most out of invested funds as well as get the most efficient growing process.
- To reduce light loss by optimizing the spacing and height of the fixtures. This means planning the lighting configuration so that the biggest part of illumination will be directed to the crops and in a way that the optimal light intensity area is as large as it can be. This decision helps to get the most efficient use of lighting from each used Watt of energy.
Reaching these goals is a process of trial and error and in practice means tweaking the parameters many times before the optimal light plan is chosen. When doing the simulation, the light planner takes into consideration the installation height of the fixtures, placing of the tables, gutters or pots in the space and the reflection factor of all objects and materials in the space. Typically, greenhouse glass will reflect 6% of the light back onto the crop, while clean, white walls of a growth room or chamber will reflect 70%. The amount of illumination that will come back to the crop also depends on the distance of the reflecting wall from the crop. Luckily, light planning software is equipped with the capability to calculate this.
Figure 3 – A sample rendering of a lighting configuration and light distribution map for a greenhouse. The ideal to strive for is: greatest possible optimal light intensity area with a minimal number of luminaires.
Figure 4 – A sample rendering of a lighting configuration and optimal light intensity area for a multitier growth environment.
A mistake in any of the steps listed above such as inadequate micromoles level, incorrectly chosen type of luminaire or badly positioned light elements will reduce the quality and quantity of the harvest. The most common mistake during the light planning process is inadequate configuration of lighting layouts that does not consider the most efficient luminaire positions, mounting heights and quantity of lamps.
Light planning software applications like Dialux do make this process easier. Nevertheless, a good planner has extensive knowledge in optics, physics, environmental issues, electricity, photobiology and horticulture. Having a professional, comprehensive light plan ensures optimal returns from the grow lights investment. For researchers, it is reliable data, for growers it is profits and for consumers, high quality products.
A good light plan at its best saves time and money. The light plan works as a solid, reliable base for the sales process of the lighting manufacturer. When the fixtures are sent to the customer, the electrician is then able to make the installation correctly by looking the exact installation height and distance between lamps from the light plan.