The first three questions in the proper characterization of an agronomic lighting solution

1. Which spectrum do I need?

Agronomic light spectrums need to suit the plant, the growth stage and projected result. Changes in the spectrum can affect the biomass of the flower, the ability of the plant to absorb light energy, the growth rate, color, height, size of root system and more. Pay attention to this point and research it as it is critical to success.

2. Which light intensity should I provide the plant?

First, when answering this question, decide where you are measuring. What is the measuring height? Whereabouts on the plant? What is the distance from the lighting fixture?
Different plants, at different growing stages, need different energy levels. This doesn't always work on "more is better". There is a saturation point where any extra light can damage plant development. Even if you decide to supply lighting close to saturation point, be careful not to give more. Overlighting can cause tip burn, stress, deformities, overdeveloped root systems and other side effects. Lack of light can cause delayed flowering, low affectivity and lengthening of intermodal spacing.
It is important to remember that the answer on light intensity is also related to the other two questions.
The intensity that you measure in PPFD must relate to a specific spectrum. In different spectrums, the light intensity will have different influences and effects. I've explained this in my article PPFD - 100 micromol per square meter per second ≠ 100 micromol per square meter per second.
The intensity with which we choose to work will also affect the answer to the third question. In answering questions 2 and 3 we are, in effect, characterizing the DLI we will work with.

3. How long to illuminate?

The length of illumination during a 24 hour period is highly important and will be a vital ingredient in your influence on the plant. Dark hours are no less important than light hours. To characterize our solution, we must research the maximum and minimum lighting time that can be given the plant in order to achieve the desired result.

I usually recommend that we decide on the maximum number of hours of daylight we can give. The reason for this is that if we work with the maximum, we can use lower levels of illumination which both lessens the cost of arrays and lessens heat emission from the lighting fixtures.

In many cases we choose the duration by the DLI we target. Here there is also a recommended DLI range decided by the needs of the plant and each growing stage. The intensity level that we characterized in question 2 relates to the amount of energy measured per second. DLI relates to the amount of energy per 24 hours. The multiple of the answer to question 2 by the answer to question 3 will determine the DLI and this is the link between these questions.