Quality of Light Part 1- LED Grow Lights - The power of good lenses
For the past decade LED light source has quickly pushed out of the way the traditional light sources in every possible application - residential, industrial and even street light. Due to the complex biological processes connected to the quality and quantity of light LED is yet to become the preferred choice for greenhouse illumination.
The main argument pro the benefits of the LEDs, regardless of the application, is efficient conversion of light and lower energy bills. Thus many manufacturers are trying to increase the the efficiency of their fixtures. When we are talking about grow light efficiency, we need to abstract ourselves of the general illumination idea of efficiency and use the amount of photons that are causing photosynthesis, thus grow light efficiency is measured in μmol/s or μmol/w. For more information on the topic see the article below "Why we need to phase out the term "lux" in horticulture"
While definitely increasing the fixture's efficiency is a desirable attribute and strong marketing tool for sales, growers and buyers must know that efficiency is simply the improved light conversion of the fixture and photosynthesis is based on the amount of photons reaching the plants, NOT emitted from the light. Depending on the application the fixture is applied for it might be smarter to include optical lenses to ensure that the efficiency you have invested in so much, is not diluted by the law of physics. In series of article, we are going to show good examples of how quality of light is as important as quantity.
To illustrate the power of good optics (depending on the application), we have run a small experiment with simulation using 3 fixtures. All the fixtures are using the same heatsink. Fixture A and Fixture B are identical except for the lenses, using same Meanwell HLG 150W Driver and same LED sources (Oslon Square 660 nm bin VMVO and Nichia Warm White NF2L757GRT). Fixture C is using Magenta LEDs with Inventronics driver 150W
The simulation area is standard 4x4 ft (1.2 x1.2m) with two fixtures installed at height 2 ft (0.6m).
The results are included in pictures below:
Results from fixture A:
Results from fixture B
Results from fixture C
Based on the results we can draw the following conclusions:
The average μmol/s/m2 value of fixture B is 23% higher than fixture A (though both are having the same efficiency), thus plants are having more energy with fixture B
The light distribution under fixture B is more uniform than Fixture A
The average μmol/s/m2 of fixture A is 26% higher than fixture C, efficiency of fixture A is also 23% higher than fixture C. Maximum μmol/s/m2 of fixture A is only 7% higher than fixture C. However the price of Fixture A is 35% higher than fixture C
Investment in high efficiency LED package is worth it, but to further optimize the system, using lenses is a good choice in selected applications.