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Switching from HPS to LED


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This article explores what to consider when switching your grow from high pressure sodium (HPS) to light emitting diode (LED) based grow lights. Based on scientific evidence gathered by Dr. Ben Higgins. Ben works with both Gold Leaf Gardens and KIS Organics. He is the research scientist for Gold Leaf. Ben also works with KIS Organics assisting with product development and research.

Ben earned his Ph.D. in Ecology and Evolutionary Biology from the University of California, Santa Cruz where he studied functional ecology, organismal morphometrics, and physiology.

Why switch from HPS to LED

The biggest reason to switch from HPS to LED is cost saving. The cost of electricity has been increasing rapidly in South Africa. Conversely, the efficiency of LED grow lights have been increasing at a rapid pace. Therefore, growing with LEDs not only lowers operating costs, it is also able to increase yields dramatically.

Ben wanted to follow a scientific approach to ensure he gets the most out of the process of switching from 1000w Gavita HPS to LED grow lights. Not only trying to find the best way to switch, but also attempting to discover how LEDs affect yields and terpenes.

The scientific approach to switching

Ben grew three different strains under four different lights, while keeping all other variables the same as far as possible. The first data point was weight, not just total weight but wet and dry weight of the flowers produced. The image below shows the results of the wet weight measurements.

Switching from HPS to LED

Three cultivars grown under 4 different lighting fixtures (3 LED, 1 HPS). Both Animal Sherbert #2 and Wedding Cake produced more wet weight when grown under LED light B, followed by LED light C and then LED light A, respectively. Apricot Jelly preferred LED light A (LED light C was unavailable for testing this cultivar). Regardless of LED light fixture, they all outperformed HPS fixtures.

All the LED fixtures outperformed HPS significantly. However, Ben also tested different stages of growth under HPS and LED grow lights. Starting a clone under LED and moving it to HPS stressed the plant considerably. Conversely, starting the clone under HPS and moving it to LED the the plant was doing just fine.

Moving a plant from HPS to LED requires the intensity of the LED grow light to be lowered until the plant has adjusted. This is because the LEDs produce a more intensely focused light to enhance canopy penetration. Lastly, the coverage area of HPS tends to be larger than LEDs because of the focusing of the light by LEDs.


This article was created from the podcast by KIS Organics. Episode 69.

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