Why are lighting plans so important for agriculture?

When planning agronomic lighting for agriculture, the emphasis is on different parameters than light planning for spaces meant for people.

Our expectations for these lighting plans are different because the users, conditions and end results are completely different.

When lighting an office we take into account who will be sitting under the light - a person. Therefore the parameters on which we focus when checking the planning results are, for example: lighting intensity, glare, color temperature, Color Rendering Index (CRI) and uniformity.

Moreover, also in lighting standards, correct planning is based on these parameters. That's how the world of professional lighting operates - the planner sticks to the recommended standards and designs the plan to take into account all relevant parameters. There are detailed recommendations in the international standards for lighting interior and exterior spaces, roads, classrooms, sports fields etc.

SPD

One of the first parameters that need to be evaluated is the spectrum put out by the light fixture used in planning and it's Lighting Efficacy (lm/w) in the specific spectrum. It's also important to know the SPD to be sure this is what is necessary for your plants.

Lighting levels

Another important parameter is the lighting level at the plant canopy (PPFD) which we achieve. We must check that the result in the plan is consistent with what the plant needs, how many hours it takes to reach the desirable DLI and how this affects the electrical needs of the facility.

Heat emission

The third parameter is heat emission from the light fixtures (BTU/H). This parameter has an effect on the immediate climate which ultimately affects plant growth in the facility. The lighting planner must take this into account. But only taking into account isn't enough. It is best to work with a planner who is in touch with the agronomist or air control planner for the facility, in order for them together to create the optimal climate for the plant at each of its development stages.

Light uniformity

One of the most important parameters in agriculture is light uniformity, much more so than in lighting for humans. If it's accepted in an office to plan lighting around desks at 1:3 ratio between minimum and maximum and, in the total space of 1:5, in an agricultural facility this is amateur planning and not acceptable. A plant receiving low light intensity will have less energy and develop slower than the plant next to it which is receiving higher light intensity. If we've already invested in building a modern facility which will use advanced technology such as lighting, then we assume that one of the requirements for the facility is that the product grown will be uniform and repeatable. A growing area that divides plants into those which receive 100% intensity and those which receive 20-30% will have different sized plants, developing at different rates, with a different end product.

Number of fixtures

Let's take the easiest example of an area 9.6m x 20m and we hang a fixture from the center; we intuitively understand that the light level drops towards the edges of the area. If, in the same area, we hang 1000 fixtures it would seem that lighting will be more uniform.

Distance from plant

The further we hang the lighting fixtures from the plant canopy, we will probably be reducing the difference between maximum and minimum in lighting levels over the area we are measuring. However, on each increase of distance we pay a heavy price in light intensity (inverse square law), which translates to energy and a lot of money.

Photometry

The smaller the light source, the easier it is to shape the beam. This is a basic law of physics which helps us see one of the advantages of LED lighting. We can better use the photometry of the fixtures to conform to the size of the space, the lighting demands, height of installation and distance between fixtures in order to achieve a uniform result.