The Truth About LED and HPS Lighting for Indoor Growing

In recent years, light-emitting diodes, or LEDs for short, have carved out their place in the indoor lighting world — and given rise to a lot of questions. Can LEDs produce the same high-quality flower as high-pressure sodium (HPS) lamps? Will they save you money? And what are the drawbacks of LEDs that companies aren’t telling you?

HPS lights have long been the industry standard. And as the saying goes, “if it isn’t broken, don’t fix it.” It’s true; there’s nothing wrong with high-intensity discharge (HID) technologies like HPS. In fact, HID lamps might be best for your application and budget.

But, if you’re reading this, you’re probably ready to tap the benefits of LEDs — benefits which include increased efficiency, cost savings, higher light intensity, and a level of control over the lighting spectrum that’s impossible with HPS. Even better, LEDs can give you an overall healthier plant. So, let’s take a look at the two technologies to see which is right for you.

Comparing LEDs and HPS Lighting

Generalizations about LEDs — or HPS lamps, for that matter — lead to some bad conclusions. With horticultural lighting, it’s all too easy to make apples-to-oranges comparisons. That’s why many growers have had disappointing experiences with LEDs in the early years.

LEDs have varying efficiency ratings, depending on the product, and that dramatically affects how much light they’re producing. It’s the same with HPS. When we talk about HPS technologies in general, we gloss over important design elements like (1) the wattage of the fixture, (2) whether the lamp is single- or double-ended, and (3) whether the ballast is magnetic or electronic, etc.

For instance, an HPS fixture may achieve an efficiency of 1.7 µmol/joule if it’s a double-ended lamp with a 1000-watt electronic ballast. But a different, 400-watt HPS light with a magnetic ballast is a different story. The 400-watt will only score an efficiency rating in the 1.0-µmol/joule range. Essentially, we’re talking about different technologies and calling them both “HPS.”

LEDs are much the same. Though they’re generally more efficient than HPS (with some clocking 2.8 µmol/joule), some LEDs are less efficient than high-quality HPS fixtures, and they give you less light. You’ll find the LED fixtures vary in efficiency based on (1) the type of diodes, (2) the color composition of the spectrum, (3) the product’s overall quality, and other engineering factors. What’s more, even if the µmol/joule efficiency is high, an LED fixture may not have the spectrum to give your plants good morphology, as explained below.

You may also find some hidden inefficiencies lurking in the ballasts of HID fixtures. All too often, the µmol/joule rating on HPS products states the lamp efficiency, not the actual product efficiency. The lamp may perform well in a laboratory setting based on the wattage provided, but when the electrical loss of the ballast is factored in, the efficiency numbers begin to look very different. The reflector hood also decreases the stated efficiency of an HPS fixture.

In truth, efficiency goes beyond electrical consumption. Well-engineered lighting products will provide you with better harvest outcomes for several reasons. For instance, when you give your plants a balanced, fine-tuned spectrum, you can expect an increase in secondary metabolites and larger crops of denser flowers. And electrical efficiency means lower heat, which creates a cascade of cost-reductions due to reduced HVAC use, fewer circulating fans, and easier pest management.