Grow Light Intensity and It’s Optimal Mounting Height

In the last article, we covered how lighting uniformity could improve the overall health and yields of plants, as well as how it could help growers save utility on irrigation.

Besides uniformity, there are other factors of a grow light system that need to be considered to achieve an efficient and successful growing system. In this article, we will address the importance of lighting intensity in a system. What is Light intensity? Why is light intensity a crucial factor to look at when choosing a grow light system?

Before we jump into this topic, let us address two common misconceptions that people have when they are switching from traditional HID grow light to LED grow light systems. People often mistake wattage being the intensity of a grow light system.

Watt () is a measure of electrical power in a lighting system, it is how much electrical energy is needed for a grow light system needed to operate. Another misconception is that people use lumens to justify the intensity in a grow light system.

Lumen () simply refers to the visual brightness of a light source to the human eyes; It doesn’t indicate how much or well the plants will utilize the light.

Now we know that wattage and lumens are not indicators of the light intensity of a grow light system. Then what’s the light intensity in a LED grow light system?  In a grow light system, lighting intensity is measured in the unit of μmol/second as PPF (Photosynthetic Photo Flux). PPF measures light intensity by examining the number of photons generated per second by the light source. Thus, the higher number of photons generated by the light source, the higher the light intensity. Why is light intensity important in a lighting system? Light intensity is directly linked to crops’ yield. Now you might think the higher the light intensity, the better yields will come from the crops. All crops have a point where too much light will be hazardous; photosynthesis reaches its maximum rate and that is the light saturation point.

In a real-life situation, we need to consider adjusting the mounting height to reach the optimal lighting intensity for the crops. Now we understand PPF, then let’s talk about PPFD. PPFD is Photosynthetic Photo Flux density. It is the same concept as PPF but takes a defined area into account. We can use PPFD to determine the optimal mounting height.

In order to make sense of these PPFD values, you need to understand the range of light levels for growing fruiting or flowering crops such as Cannabis or Tomatoes, where:

The optimal light intensity for a controlled environment is 600 to 1100 μmol/second/ m2. The added intensity no longer promotes growth rate but also damaging to the plants.

Then how do we utilize these numbers?

Figure 1. Is a visual representation of the inverse square law which shows the relation between mounting distance and canopy area.

Inverse Square Law : In science, an inverse-square law is any scientific law stating that a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity

We can refer to Figure 2. for a quick check for mounting heights. Effect of different light levels on plant growth and the distance away from a light source in order to fall within said range.

For example, HYDRA 720W has an intensity from 462 to 1,048 μmol/second/ m2   , which is optimal for the plant’s growth when the surface is  12” and 18” away from the light. This is the best distance for your plants to ensure maximum growth.

Figure 2. Color-Coded Lighting Intensity and Its corresponding Mounting Height

A high-intensity lighting system is a good indicator of an efficient system, however; growers need to understand how to utilize these robust systems to reach their full potential. We have covered the calculation on PPFD and its optimal corresponding mounting height.