What’s the difference between a Metal Halide or High Pressure Sodium (MH / HPS) grow light, and an LED grow light? Let me help you decide which one is best for your garden.
Many people are tempted to purchase LED grow lights simply because they consume less energy. But there are still situations where an MH / HPS grow light is the better choice.
HPS vs LED Grow Lights - Key Differences:
Energy Consumption
I estimate LED grow lights are equal to HID grow lights that consume 33% to 50% more power. For example, a 450 watt LED grow light would be equal to a 600 watt MH / HPS grow light. The 630 watt HLG 650R is supposed to be equivalent to a 1000 watt double ended HPS grow light.
But in some cases, like in a 4×4 foot grow space, you could still end up using similar wattage between HPS and LED grow lights.
For those who use a 400 watt HPS grow light in a 4×4 foot space, a proper LED alternative for 4×4 feet consumes between 400 and 500 watts. So there would be no energy savings there. If you’re using 600 watts in a 4×4 foot space you’d be able to save 100 to 200 watts.
It’s important to make sure you’re comparing true wattage of the LED grow light to the wattage of the MH / HPS. A lot of new growers are confused by the number in the light name, for example a Bestva 2000 watt grow light really only consumes about 400 watts. The 2000 number comes from two hundred 10 watt LED chips used in the light.
Up Front Cost vs. Long Run Cost
Even though the popularity of LED grow lights has overtaken HPS grow lights in modern gardens, there is still a significant cost difference. Are LED grow lights worth the extra cost?
A proper LED grow light for a 4×4 foot grow space can cost between $400 and $900, while an HPS grow light will cost (sometimes significantly) less than $200.
I understand not everyone is concerned with up front cost. But I still encounter a lot of budget growers who need the best bang for their buck.
Let’s take a look at hypothetical energy cost difference between an HPS and LED grow light for a 4×4 foot grow space. Feel free to check out my Grow Light Cost Calculator and plug in your own scenarios.
Let’s say you’re choosing between a 600 watt HPS and a 450 watt LED grow light for a 4×4 grow tent. At the time of writing you can get a 600 watt MH / HPS kit for $140 - $170. A common 450 watt LED grow light for 4×4 costs $470.
For the sake of simplicity we can pretend you’re growing autoflowers which require 18 hours of light from seed to harvest. A power saving of 150 watts at the US average electricity cost of $0.13 per kilowatt hour means you’d save ~$10.50 per month in electricity if you bought the $470 LED grow light.
It would take 29 months for the cost savings of the LED grow light to save you the extra $300 you spent on the LED light.
Spectrum Quality
HID grow lights require the use of two different bulbs. One is a metal halide bulb that creates a blue spectrum for the vegetative growth phase. The other is a high pressure sodium bulb that creates a red spectrum for the flowering phase.
The bulbs generally last between 20,000 to 35,000 hours, where LEDs are said to last up to 50,000 hours. The bulbs are fairly cheap and easy to replace, whereas LED grow lights need to be shipped to manufacturers for warranty repair on the rare occasion the LEDs go out early.
It’s been documented in university studies that growing plants with white light spectrum, like the spectrum produced by modern LED grow lights, is superior to using red and blue light wavelengths alone.
Tomato yields were 12% to 16% better when using white light found on modern LED grow lights.
Some modern LED grow lights also include infrared and ultraviolet diodes, each which have specific benefits for growing cannabis.
Heat
HPS grow lights are known for high heat output. If you’re unable to control your climate well, it may be worthwhile to get an LED grow light. If you have a portable A/C or an otherwise well controlled climate, you should be able to manage the heat of HPS grow lights.
Certain LED grow lights, like the ones from Mars Hydro, feature extra long power cords attached to the power drivers, which allows you to hang the drivers 6 feet away, presumably outside your grow tent for better heat management.
Feel free to check out my guide to keeping your grow tent cool.
Light Spread
Metal Halide and High Pressure Sodium grow lights can create very centralized light, depending on the setup. The open wing style reflector is best for light spread, but not everyone uses it.
Modern LED grow lights have gotten much better at spreading light evenly across the canopy. I’d argue they’re definitely better at uniform light spread than MH / HPS grow lights.
If you’ve used the old boxy style LED grow lights with fans on them, and now moved to the newer multi-bar style or quantum board style LED grow lights, you know there’s been a big improvement!
When to Use HPS Grow Lights instead of LED Grow Lights, and Vice Versa
If you’re stuck wondering which type of grow light to use, I’ll explain what I usually recommend. Of course you should also take into consideration what I’ve laid out above.
HPS if you’re on a budget growing more than one plant
If you’re growing more than one cannabis plant on a budget, an HPS grow light is probably the way to go in terms of bang for your buck. As I mentioned earlier, you can light a 4×4 foot space with a 400 or 600 watt HPS grow light for well under $200.
LED grow lights for higher quality cannabis
I’m not saying you can’t grow good cannabis with HPS grow lights, but science says certain light wavelengths produced by LEDs is beneficial - such as ultraviolet, infrared, and the other colors included in white spectrum grow lights. If spending a bit extra on LEDs isn’t a big deal for you - I highly recommend them.
Big Grow Space = Big Decisions
If you’re growing in a large area, you need to decide between spending a large sum now and having a lower expense after a few years, or spending less now, but higher electricity expense throughout. Here’s an example:
A 20 x 20 foot grow area would require 16 grow lights that cover 5×5 feet each. In other words you can spend 16 x $900 for LED grow lights that cover 5×5 feet each, or you can spend 16 x $190 for 1000 watt HPS grow lights.
The upfront cost difference is over $11,000. The electricity difference would theoretically be ~$25 extra per month for each HPS grow light, assuming $0.13 per kilowatt hour (average US cost) and 18 hour light days.
After 27 months of 18 hour light days the extra $25 per month you’d spend on electricity for each HPS light would equal the $11,000 you would have spent up front on LED grow lights.
The difference is if you initially decided to buy LED grow lights, after 27 months you’ve saved back your $11,000, and you’ll continue to spend $25 x 16 less on electric per month than if you chose HPS grow lights.
Commercial growers may choose to spend more up front on LED grow lights and reap the electricity savings a few years down the road.
Final thoughts
HPS grow lights still have their uses, even if they aren’t as popular anymore. I hope this discussion helps you along in your decision.
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