HPS Grow Lights: Pros, Cons and How to Use Them

The main advantages of high-pressure sodium (HPS) grow lights are a cheap upfront price, a warm spectrum that pushes heavy flowering, and a lot of heat that helps in cold grow rooms; the trade-off is higher power bills and more heat to manage. Light is everything in a cannabis grow: no light, no life. That's why growers have to weigh different light types and figure out which fits their setup best: big or small grow, budget, strain, plant height and so on.

One of the many options on the market is the sodium lamp. So what's it good for, and why do so many growers recommend it?

What are sodium vapor lamps used for?

Sodium lamps have a reputation as a great choice for growers without much experience, or people just starting out with their first cannabis plants.

Sodium vapor lamps first hit the lighting market in the Netherlands in the early 20th century. Keep in mind there are two kinds of lights with sodium inside: low-pressure sodium (LPS) lamps and the ones growers actually use, high-pressure sodium (HPS) lamps.

Low-pressure vs. high-pressure sodium lamps: what's the difference?

Low-pressure sodium bulbs are super efficient, since they put out more lumens per watt than high-pressure ones. HPS bulbs, on the other hand, produce fewer lumens than LPS but have a much better light spectrum for plants. And here's a fun fact: you've definitely seen them before, because they're the orange lights used on highways and streets.

How far should an HPS light be from your plants?

In an indoor grow, lighting is make-or-break. When it comes to figuring out how far the light should hang above the plants, a lot of growers take the bulb's wattage and drop the zero to get the distance in centimeters. That doesn't quite work with sodium lamps, though. With HPS, you need to add another 5 to 10 centimeters (2-4 in). Here's a quick guide:

• 250 W sodium lamp = roughly 25 to 35 centimeters (10-14 in).
• 400 W sodium lamp = keep at least 40 to 50 centimeters (16-20 in) of distance.
• 600 W sodium lamp = at this wattage, the light should sit 60 to 70 centimeters (24-28 in) above the plants.
• 1000 W lamp = with these bulbs, keep the plants at least 1 to 1.1 meters (about 3.3-3.6 ft) away.

Because these bulbs run hot, it's crucial to keep a close eye on the temperature at the tops of your plants. Use a thermo-hygrometer (a combo temperature and humidity meter) and place it at canopy height, right at the top of your plants.

Benefits of HPS grow lights

An HPS lamp makes light by firing a high-voltage pulse through a pressurized arc tube filled with sodium vapor, plus other elements like xenon and mercury. The full setup includes a ballast, a reflector and one or two bulbs.

All that adds up to several benefits for an indoor grow:

• Great for flowering: HPS lamps give plants a serious boost during the flowering stage, so they bloom with more vigor, which translates into bigger yields.
• Lower upfront cost: LEDs get all the credit for saving money, but HPS lighting systems are actually cheaper to buy than LEDs.
• They fight the cold: they're known as a grower's best friend in winter or in places with harsh freezes.

Downsides of HPS grow lights

• Power consumption: a lot of the electricity is lost as heat, so your power bill goes up.
• Shorter lifespan: this applies to the system's components.
• Too much heat: you'll need extra gear to keep temperature and humidity under control.

Which sodium lamp does your grow tent need?

• In an 80x80 cm tent, use a 250 W sodium lamp for 6 containers of 11 liters (about 3 gallons).
• For 100x100 cm, use a 400 W sodium lamp for 9 containers of 11 liters.
• For 120x120 cm, go with 600 W for 11 containers of 11 liters.

How does an HPS lamp work during flowering?

As we mentioned, one of the biggest perks of HPS shows up during flowering. HPS lights are best known for their yellow-orange glow, which also shows how old the technology is: most of the lights on the market today give off blue or white light.

That warm, red-heavy spectrum resembles late-season sunlight, and growers say it pushes plants to stack buds harder than other lights would (the switch to flowering itself still comes from the light schedule).

To get the most out of this, you can find dual-spectrum HPS bulbs, which are popular because they work for every stage of a cannabis plant's life. They also offer a somewhat broader spectrum than flowering-only bulbs.

What to know before you use HPS lights

Keep in mind that these bulbs behave totally differently from the other lights on the market. The lights you're used to turn on pretty much instantly, while high-pressure sodium lamps warm up gradually, so it can take 3 to 5 minutes before they reach full brightness.