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HPS VS. LED: Which One Is Better?

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February 28, 2020
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    The attraction with indoor cannabis cultivation is understandable. Storms, heat-waves, cold snaps and pests do not (in theory, at least) affect the indoor grower, nor do little details like season and climate. 

    For as long as we can remember, HPS and HID lamps have been the only way to guarantee BIG yields, but LEDs have been gaining on these market leaders. The question is, have they caught up?

    While indoor cannabis grows have plenty in the pro column, one definite con is the lack of natural sunlight (unless you live in a greenhouse, which is not as much fun as it sounds). But this is where your lights come in. There are plenty of grow lights on the market, but for cannabis cultivation, you need to get specific. A certain light might be fine for lettuce and tomatoes, but will it pump enough power into a cannabis plant? Enough to measure yield in pounds instead of ounces? Will it work for all stages of your grow? Remember, farming watercress is NOT the same as farming hash.

    HPS Grow Lights

    High-Pressure Sodium (HPS) lamps are a type of gas-discharge light that, as the name suggests, operate at a very high internal pressure. They consist of a narrow arc tube within a bulb. Sodium, mercury and xenon are the three elements inside the tube, used at different stages of ignition (and for different colored light). The tube itself is an aluminum oxide ceramic, resistant to the corrosion of alkali metals like sodium.

    Light is produced when electricity arcs through the tube. An ignitor sends an electric pulse through the xenon gas, emitting sky blue light as the xenon heats up. The xenon heats up the mercury which emits more blue light, raising the temperature and vaporizing the sodium at over 460˚F, resulting in the bright white light (full of yellow and red, with a little blue) that mimics full, summer sun.

    Pros

    For a very long time, HPS grow lights have benefited indoor cannabis cultivation in many ways:

    • Cheap Start-up Cost. Since the technology for this grow light has been around for so long, HPS lights are inexpensive to produce. Even the high-end varieties cost less than most LEDs. Moreover, HPS lights are modular so if one bulb in the set-up fails, it can be changed without replacing the entire system… the go-to choice for cultivating cannabis on a tight budget.
    • Massive Light Output. HPS bulbs produce an immense raw light intensity that’s beneficial for growing plants with large yields. For this reason, HPS is best used when cultivating large quantities of cannabis in a bigger grow space.
    • Prolific Yields. Since HPS lamps deliver more towards the yellow/red part of the light spectrum, they are perfect for the fruiting/flowering stage of your grow. This, coupled with the intense light output, make HPS lamps unrivaled when it comes to growing huge yields of dense buds.
    • Easy to Use and Helpfully Generic. HPS grow lights are easy to install and are often available in novice-friendly kits. Unlike LEDs (that vary massively in quality, power and efficiency across different models and brands), the light and heat emission of HPS grow lamps is predictable and almost indistinguishable from model to model. This is important when gauging the right plant-to-lamp distance to successfully grow buds.

    Cons

    Although HPS grow lights are the standard, modern lighting system for growing cannabis, they are not without drawbacks.

    • Extreme Heat Emission. One downside to the enormous light output of HPS growing lamps is that they generate lots of heat. LOTS. This means additional ventilation equipment to control temperature which, in turn, creates additional expense. While the lights pump out energy, the plants can succumb to the Icarus effect, scorching leaf tips and colas that reach too close to the bulb. You have to be vigilant with HPS lights: keep the tent cool and maintain a good distance from plant to light.
    • High Power Consumption. HPS growing lights can consume up to (and sometimes over) twice as much electricity as LEDs. This adds a heavy burden to your overall budget and one you must consider before your trip to the Hydro store.
    • Limited Spectral Output. HPS grow bulbs produce the yellow-red light ideal for the flowering phase of your grow. They are less effective during the vegetative stage, however, which means purchasing separate blue-colored bulbs – usually metal halide.
    • Omnidirectional. The light produced by HPS bulbs is scattered 360 degrees. This reduces its efficiency as almost half the generated light needs to be reflected and redirected to the desired area. This means more accessories to focus the light where it’s needed.
    • Short Lifespan. Another drawback of using HPS bulbs is that the light intensity diminishes over time. All HPS bulbs will eventually start consuming more electricity while producing less light, an unavoidable drawback.
    • Waste Disposal Issue. Since HPS bulbs contain small amounts of mercury, disposing of broken/expired bulbs becomes a problem. Mercury is toxic and poses a threat to the environment. Make sure you know where to take your perished bulb – the store you bought the bulb at is a good place to ask.

    How To Use HPS Lamps

    Growing cannabis plants using HPS lights requires setting up the different components that make up the lighting system. To create optimal growing conditions, you’ll need to learn a little about wattage, plant-lamp distance and temperature regulation.

    Choose The Right Accessories

    Choosing the best components is key to getting the most from your HPS grow lights.

    • Reflector. With an omnidirectional HPS bulb, a hood must be used to focus the light on the plants. There are many models available, the best ones being air-cooled hoods that fully enclose the bulb. They are glass-bottomed and can be equipped with exhaust fans. Make sure they have at least a 6-inch vent hole on both ends to ensure maximum airflow and cooling. Vent holes help diffuse the excessive heat emitted by the lamps.
    • Ballast. This regulates the current and provides the required voltage to start the lamp. Without it, the lamps will overheat and burn out. Ballasts also produce a significant amount of heat. It’s best to opt for either a remote or digital ballast if your budget allows.

    Remote ballasts have a long cord allowing them to be placed outside the grow room. A digital ballast uses computer chips to draw sufficient electricity to power the lights. They are widely regarded as the best kind out there because they maximize light output while simultaneously consuming less power.

    Determine Appropriate Wattage

    The appropriate wattage is dependent on the size of the grow space. Work towards at least 50 watts per square foot, 60 to 75 is acceptable.

    Recommended Minimum WattageSize of Grow Space
    200 watts2 ft x 2 ft
    450 watts3 ft x 3 ft
    800 watts4 ft x 4 ft
    1250 watts5 ft x 5 ft

    Set Grow Lights to the Correct Distance

    HPS grow lamps give off a serious amount of heat. You will need to maintain a large gap between the plant and the light source. It has to be hung over the vegetation at a distance that is relative to its corresponding wattage. Putting enough gap between the two will prevent the heat from overwhelming the plants.

    Recommended Distance Based on Wattage
    WattageClosest DistanceFarthest Distance
    150 W8 in (0.67 ft)12 in (1 ft)
    250W10 in (0.83 ft)14 in (1.17 ft)
    400W12 in (1 ft)19 in (1.58 ft)
    600 W14 in (1.17 ft)25 in (2 ft)
    1000W or over16 in (1.33 ft)31 in (2.6 ft)

    Increases in the plant-lamp distance means decreases in intensity of coverage, but it does mean the lamps  cover a larger area. It is important to check the height of your plants regularly, lights must never be placed too close or too far from the plants.

    Install An Exhaust System

    An exhaust system is the key to regulating the temperature inside the grow tent, keeping it within the optimal range. The exhaust run should be as short as possible because the farther the air has to travel, the more inefficient the system will become. Keep the run as straight as possible to ensure a smooth air flow. If possible, vent the exhaust near the top of the tent or room – the warm air will rise naturally and pull cooler, fresh air back into the space.

    LED Grow Lights

    Light Emitting Diodes (LED) are electrical devices that rely on two diodes – an anode and a cathode – to generate light. Standard diodes are made from semi-conductive elements such as silicon or selenium. When current passes in through the anode and out through the cathode, visible light is produced.

    Pros

    LED grow lights are already the most efficient lighting system around. But what else are they good for?

    • Low Waste Heat. LEDs produce far less waste heat than their HPS and HID counterparts. This means less cooling of the grow space and a far lower chance of plant burn – especially when it comes to growing in confined spaces.
    • Energy-efficient. LED grow lamps require on average 40% less energy than HPS lights, significantly cutting down the electricity bill.
    • Wide Range of Spectral Output. LED cannabis grow lights are capable of a range of light color, and can be optimized for the entire growing cycle of marijuana plants. While HPS lights are most useful during the flowering phase, LEDs may be used for both the flowering and vegetative stages, as well as the early, seedling stage, eliminating the need to buy separate bulbs.
    • Longevity. Unlike HPS grow lights, LEDs are renowned for their longer lifespan: 50,000 to 100,000 hours of constant use. 

    Cons

    The benefits of LED grow lights may be plenty, but they do have their limitations.

    • High Initial Setup Cost. Despite the good return on investment, an LED grow light system has a large, upfront cost. You’re looking at hundreds of dollars each for LEDs and there are a lot of bad products to watch out for.
    • Light Color. The purplish hue of LED lights is conspicuous and unpleasant to the eye. Also, the low lighting might mask problems such as pests and malnutrition. When using LEDs, be sure to switch to whiter lights to periodically check the health of your plant.
    • Heavy. Top-quality LED grow lights come with heat sinks that add weight. This could mean reinforced framing that can support the additional strain.

    How To Use LED Lamps

    Setting up an LED lighting system requires attention to detail such as light intensity, distance, setting and scheduling.

    • Determine the Required Light Intensity. Providing cannabis plants with optimal lighting is vital. How many LED lights are required to feed the plants properly? Typically, a single 32 watt unit should be enough to cover 1 square foot. However, this varies depending on the layout of the growing area.
    Recommended WattageSize of Grow Space
    32 watts (~30 to 40 watts)1 ft x 1 ft
    128 watts (~120 to 140 watts)2 ft x 2 ft
    256 watts (~240 to 300 watts)2 ft x 4 ft
    288 watts (~250 to 300 watts)3 ft x 3 ft
    512 watts (~500 to 650 watts)4 ft x 4 ft
    800 watts (~700 to 900 watts)5 ft x 5 ft
    1024 watts (~900 to 1100 watts)4 ft x 8 ft
    1152 watts (~1000 to 1200 watts)6 ft x 6 ft
    • Position at the Right Distance. Placing grow lights too close or too far from the plants can cause light burn or deprivation. Unlike with HPS lights, it’s tricky to measure how far LED lights should be from the plants because the models vary massively from one manufacturer to another. For most units, however, 12 – 18 inches should prove adequate.
    • Select the Appropriate Light Setting. When using full spectrum LED grow lights, selecting the right light setting is essential. Failure to do so will hinder the plants’ growth and development. The light should be set to blue (~6400 K) during the vegetative phase and red (~2700 K) during the flowering stage.
    • Establish a Light Schedule. As with the light setting, the light schedule also plays a crucial role in plant growth. Do not forget to turn the lights on and off as required. Typically, cannabis plants need 18 to 24 hours of light during the vegetative phase and just 12 hours of light during flowering.

    HPS VS. LED: The Verdict

    Choosing the right grow lights can be confusing, especially for beginners. Both HPS and LED have their strengths and weaknesses, you need to decide yourself which is most suitable for YOUR needs and YOUR budget.

    High Pressure Sodium cannabis grow lights have been around for a long time and, despite being less efficient than high-end LEDs, they get the job done. You will always get fantastic yields from an HPS, delivering a lot of bang for your buck.

    LEDs, despite being the new kids on the block, are growing rapidly. They hold significant advantages over HPS grow lights in terms of energy-efficiency, heat emission, longevity, and environmental benefits. The entire set up, however, can be financially daunting for those with a limited budget.

    So, have LEDs caught up? We think so. If you’re trying to decide what cannabis grow lights to choose, our advice would be to go for a high-quality, well-reviewed LED set-up – if you can afford it. They are easy to use, super-efficient, cheap to run and pretty as a picture. If you just can’t stomach the cost then a HPS rig will always do the job – just make absolutely sure you safely vent the excess heat and don’t fry your plants!

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