HPS lamps (high pressure sodium lamps) have been the confident leaders in the hemp lighting system market for decades, while other technologies exist but are unlikely to change their position. 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.
So what is HPS, LED (Light Emitting Diode)?
HPS lamps emit light by passing high-voltage pulses of energy through a sealed quartz tube filled with sodium vapor and some other elements, such as xenon and mercury. When heated, the gas begins to glow. Sodium emits an intense orange, yellowish light. The spectrum can be changed using xenon and mercury, which emit in the blue range of the visible spectrum, making the light whiter.
Light emitting diode (LED) lamps are semiconductors that allow current to pass almost unimpeded in one direction but provide a very strong resistance in the other direction (through a “pn junction”). On one side of the junction, the material is processed in such a way as to receive extra electrons, and on the other side, conversely, the 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.
Photoelectric efficiency
The efficiency of a lamp can be expressed in a simple formula: the total light energy of the lamp (lumens) 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 and even higher. A growing number of grow lights are also rated 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 grow lights because it measures the amount of light reaching the plant, not what the human eye sees.
The most efficient HPS lamps to date produce about 150 lumens per square meter. So, for example, a GE Lucalox 600W lamp produces 90,000 initial lumens (“initial lumens” means the first 100 hours of radiant intensity), while the best 600W Lumatek lamp produces 92,000. 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 grow lights, lm/W is considered to have less ‘speak’ than PAR. This is because the lm/W of red-blue lamps is usually much lower, as they produce the most important frequencies for photosynthesis, and the production of “inefficient” light is minimized.
However, newer LED grow lights use multiple frequencies to create a richer, more efficient and fuller spectrum, which is considered beneficial for plant growth, and often include discrete white LEDs as well as red and violet. These newer panels sometimes express efficiency in lm/W. Reputed manufacturers should at least indicate PAR. For example, a 410W full-spectrum panel (Budmaster II 675 GOD) from British company Budmaster indicates PAR values at different distances from the light (the longer the distance, the lower the PAR, as fewer photons hit the plant surface). At 31cm, the lamp has a PAR of just over 2000 µmol/s.
Spectrum
Although advancements have not avoided the development of HPS technology, these lamps have only a faint natural sunlight appearance compared to more modern lighting systems. Without the addition of xenon and mercury, sodium itself emits red-yellow light. However, new “full spectrum” lamps have emerged that actually have two arcs, i.e. they are a mix of DNAT and DRI. So, for example, the Hortilux Super Blue HPS/MH combines 600W HPS and 400W DRI to deliver 110,000 initial lumens and simulate a spectrum as close to natural as possible.
Currently, LED grow lights are probably the best in terms of frequency spectrum, as the most advanced models offer up to 11 frequencies, which are crucial for plant development.
