As a grower, you invest in supplemental LED grow lights because they power the yield and quality of your crops. In fact, the rule of thumb is that 1% light output equals 1% crop yield. So, it’s vital that your LED lighting investment delivers the full performance that you paid for.

The performance is determined by the light intensity and light uniformity of the LED grow lights that you use. If the light intensity produced by the grow lights installed is lower than what you expected from the design, there will be less yield. If the uniformity is inconsistent, individual plants will grow and develop at different rates and there will be uneven production in your greenhouse.

When you compare different lighting designs, make sure that you compare apples with apples. This means taking three things into account:

1. Verify the credibility of the performance claims that manufacturers make.
2. Make sure that DIALux calculation software is used for the lighting design. This calculation software is provided by an independent company and commonly used in the horticulture market.
3. Check which input parameters have been used for each lighting design. It is easy to tweak the input parameters and give the impression of more positive light level and uniformity within the lighting design. So which parameters are crucial?

The most important input parameters to check are:

• Has the right product been specified? Check if the exact product that you have selected for your project has been used in the lighting design, with the right light output (PPF in µmol/s) and spectrum (blue/red/white/far red/…).
• Have your specific design values been used, like the average light level at your crop (PPFD in µmol/m²/s) and the overall light uniformity?
• What are the standard settings? The height of the grow light and crop (free height), reflection factors, and the size and position of the area that is used in the uniformity calculation all have an impact on the average light level and overall uniformity achieved.

The first input parameter to check is the free height that specifies the distance between the LED module and the head of the crop. The free height can seriously impact the overall uniformity value. For high-wire tomato crops that have a limited free height of 1.50 to 2.50 m, for example, it can be a challenge to achieve a good overall uniformity value. Using an optimistic free height, or calculating uniformity at floor level as if there is no crop, will positively impact the overall uniformity value.

The free height is calculated by measuring the distance between the eventual top of the crop and the mounting height of the LED grow light.

Another important parameter to check is the reflection factor used in the lighting plan. A reflection factor indicates the amount of light that is reflected by walls and other objects in a space. DIALux calculation software was originally designed for indoor spaces like offices, where you get reflection off the walls, ceiling and floors that impact the light level on your desk. To avoid being too optimistic about the outcome, the reflection values in DIALux are set at 0% for a greenhouse lighting design, because the glass in a greenhouse does not reflect the light from the grow lights.

The next thing to check is the calculation surface that has been defined. The size of the calculation area and the position of the grow lights within that area will seriously impact the average amount of active photons that reach the surface of the crop (PPFD value in µmol/m2/s). When comparing lighting design results from different manufacturers, make sure that the calculation surface shows an equal number of maximum (peaks) and minimum (dips) light intensity values. This is the only way to calculate a realistic average PPFD value in the lighting design.

In the example below, you see two positions of a calculation area within the same light plan. Let’s assume that the light intensity peaks are located perpendicular to the grow light and the light intensity dips in between two grow lights. The values in scenario B will generate far better average light intensity values, because the light intensity is calculated over an area that shows four peaks and one dip. Scenario A shows four peaks and four dips, and consequently far better represents the reality after installation.

Another important factor is the size of the calculation surface that will impact the overall uniformity value. When comparing lighting design results from different manufacturers, make sure that the same calculation surface has been applied.

To represent a real-life situation, a calculation for the full compartment area should be made that includes the edges of the greenhouse. A calculation of the smaller centred area, which represents a typical production area, should also be made. The calculation for the full compartment will generate lower light uniformity levels, because of the lower light intensities at the edges. So, make sure that you always compare either calculations of full compartments or smaller areas within the full compartment. For example, below you see two positions of a calculation area within the same light plan. Let’s assume that the light intensity peaks are located perpendicular to the grow light and the light intensity dips in between two grow lights. The values in the scenario B will generate far better average light intensity values, because the light intensity is calculated over an area that shows four peaks and one dip. Scenario A shows four peaks and four dips, and consequently far better represents the reality after installation.

The final parameter to check is the type of uniformity being used. Uniformity can be expressed in different ways. When you run the DIALux lighting design software, it provides you with different types of uniformity. When comparing lighting design results from different manufacturers, make sure that the same type of uniformity calculation is applied. For a horticulture application, we prefer to express uniformity as the average light intensity divided by the maximum light intensity, which best represents a real-life situation.

When comparing lighting designs, there are lots of tweaks that suppliers can potentially make to their plan. If you want to make a proper comparison, you have to take a few parameters into account.

• Has the correct product, with the right spectrum and light output, been used in the calculations?
• Has the right light level for your crop and the right overall light uniformity been used?
• Are the settings comparable:
  – Has the free height been correctly defined?
  – Are the reflection factors set to 0%?
  – Does the measurement grid have an even number of light and dark spots in it?
  – Are you comparing the full compartment or small, centred area numbers?
  – And is the uniformity defined the same in the lighting designs?

Read our other blog and learn how to evaluate performance claims of an LED grow light.

You want to make sure that you get a rapid return on your investment and have all aspects of your project carried out professionally. With Signify, your project is in experienced hands. Signify is the global leader in the lighting sector and has built up a substantial track record in more than 500 projects in the horticultural lighting market since 1995. This includes over two decades of dedicated experience developing tailor-made, LED-based light recipes that help growers speed up growth, increase yield and improve the quality of plants. With cutting-edge LED innovations at our command, we can custom-build a science-based solution for you.