HPS lights (high pressure sodium lights) have been the confident leaders in the cannabis lighting system market for decades. Other technologies exist but they are unlikely to change HPS lights' status.
In this article, we'll take a closer look at the differences between the different types of lights and try to give an opinion on what to expect from them.
HPS lights emit light by passing high-voltage pulses of energy through a sealed quartz tube. The quartz tube is filled with sodium vapor and some other elements such as xenon and mercury.
When heating, the gas begins to glow. Sodium emits intense orange and yellowish light. The spectrum can be changed by using xenon and mercury, which emit in the blue range of the visible spectrum and make the light whiter.
Light-emitting diode (LED) lights are semiconductors that allow current to pass almost unimpeded in one direction but provide a very strong resistance in the other.
On one side of the junction, the material is processed in a way to receive additional electrons. On the other side, conversely, material without enough electrons is processed.
By applying a voltage, we force electrons to move through the junction to fill the "void" on the other side. This results in a glow, the color of which depends on the material used.
Phosphides and nitrides of gallium, aluminum, zinc and silicon are most commonly used here.
The efficiency of a light can be expressed in a simple formula: the total light energy (lumens) of the light divided by its total energy consumption (watts).
The minimum power of DNAT is 90 lm/W. Although for some brands, this figure reaches 150 lm/W or even higher. A growing number of plant grow lights are also evaluated in PAR (Photosynthetically Active Radiation), which is measured in µmol/s (photons per second per 1m2 of plant block surface).
µmol/s is an increasingly popular metric for plant grow lights because it measures the amount of light reaching the plant rather than what the human eye sees.
The most efficient HPS lights to date produce about 150 lumens per square meter.
Therefore, the GE Lucalox 600W plant grow light produces 90000 initial lumens ("initial lumens" means the first 100 hours of radiant intensity), while the best 600W Lumatek light produces 92000.
Although it hasn't been done before, with the new model, the HPS is starting to show and the PAR indicator. For example, the output of the Lumatek 600W is 1030 µmol/s.
For LED plant grow lights, lm/W is considered less "speaking right" than PAR. This is because the lm/W of red and blue lights is usually much lower, as they produce the most important frequencies for photosynthesis and the production of "inefficient" light is minimized.
However, newer LED plant grow lights use multiple frequencies to create a richer, more efficient and fuller spectrum, which is believed to be beneficial for plant growth and often includes discrete white LEDs as well as red and violet.
While advancements have not avoided the development of HPS technology, it is believed that these lamps only exhibit a dim natural sunlight appearance compared to more modern lighting systems.
Without the addition of xenon and mercury, sodium emits red-yellow light.
However, new "full spectrum" lights have emerged, which actually have two arcs, i.e. they are a mix of DNAT and DRI.
Currently, LED plant grow lights are probably the best in terms of spectrum. Because the most advanced models offer up to 11 frequencies, which is critical for factory development.