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HPS vs LED Grow Lights

HPS vs LED Grow Lights

Hytec Horticulture |

Since the mid-20th century, HPS grow lights have been the best available option for commercial indoor gardeners. Thus, it’s no surprise these traditional gas-discharge lights were the first choice for many farmers entering the emerging cultivation industry.

However, with the introduction of LED grow lights, more cultivators are questioning their commitment to HPS bulbs. New LED models “outshine” HPS grow lights in virtually every category, including energy efficiency, ease of maintenance, and lifetime expectancy. As a bonus, LED grow lights give off a full spectrum of light, which translates to a larger, healthier crop.

For the past 40 years, growers have had to balance growing with HPS lighting with the problem of excess heat they create and fight a constant battle with temperature throughout the seasons. Now, with the latest diodes LED grow lights pushing between 2.4umol to 3.0umol, heat is no longer the issue.

No matter the size of your grow room, it’s unlikely LED grow lights won’t help your bottom line. The initial cost will be higher than a HPS setup but savings can be made with future electric costs and by not needing bigger expensive fans and carbon filters. Instead, smaller less expensive units can be installed while also avoiding the need for expensive air conditioning units.

Before delving into the full benefits of using full-spectrum LED grow lights, let’s briefly go over what HPS and LED stand for:


HPS (High Pressure Sodium)

First off, HPS is short for “high-pressure sodium.” This gas-discharge light is so named because it produces high internal pressures versus its sister “low-pressure sodium” bulbs.

Each of these grow lights has a cylindrical aluminium-based “arc lamp” that contains a mix of chemicals like xenon, mercury, and sodium. When you turn on a HPS lamp, high-intensity voltage pulses between the arc lamp’s electrodes, thus “discharging” gas and producing light. Also, HPS grow lights come equipped with a ballast to help adjust the amount of voltage necessary to light the arc lamp.


LED (Light Emitting Diode)

LEDs refer to “light-emitting diodes,” which are tiny semiconductors that convert electrical current into visible light. Unlike gas-discharge HPS, LEDs are “solid-state” products because the light is produced between two electrodes in each “solid” diode.

It’s worth mentioning that each LED could have a different “bandgap,” which changes the number of photons admitted through each diode. These differing bandgaps help explain why LED grow lights have multiple light spectrums.

Since HPS lamps have been around longer than LEDs, many still view them as the gold standard for indoor cultivation. However, even HPS proponents have to admit LEDs address many of this older technology's inefficiencies. Let’s run through a few common pros associated with using an LED grow light.


Full-Spectrum LEDs Offer A Wider Array Of Wavelengths

In terms of light spectrums, HPS can’t hold a candle to LED grow lights. When you use HPS lamps, you’re only exposing your plants to monochromatic warm yellow patterns that have a correlated colour temperature of 2200K. LEDs, however, offer a broad array of colours ranging from 2200K to 6000K, often covering a much broader wavelength range and thus have much higher CRI.

While manufacturers could produce LEDs with specific light frequencies (e.g. red, blue, UVa), full spectrum LEDs offer a wide assortment of colours. To date, full spectrum LEDs provide better quality and yields versus HPS (per watt/joule of energy consumed).


Enjoy Longer Service Life With LED Grow Lights

As mentioned, HPS grow lights come equipped with a ballast to help adjust the amount of voltage necessary to light the arc lamp. As time goes on, HPS lamps require more voltage to produce the same amount of light, gradually losing efficiency until it eventually breaks after about 24,000 hours. Moreover, HPS grow lamps tend to flicker at the end of their lifecycle.


By contrast, LED diodes won’t degrade as quickly as a HPS grow light. This is because LEDs require no high concentrations of gas, which inevitably “burns out” rather quickly. Being more efficient, they also produce much less heat, placing less stress and wear on components over time. Most LED grow lights last between 50,000 to 100,000 hours.


LEDs Will Keep Your Grow Space Cool

Another issue with using HPS grow lights is they give off a ton of heat. Indeed, HPS lamps produce so much heat that growers need to invest more money into cooling technologies, consuming additional electricity and potentially even extra water. The excess heat from these lamps could also be a safety hazard.


With LED grow lights, you won’t have to worry about managing excess ambient heat in your grow space. In fact, most LEDs only give off about 25 percent radiant heat versus 50 percent for HPS lights. You can rest assured that far more of the energy going into your LEDs turns into light rather than heat.


Concentrate Your Photons With Superior LED Directionality

Not only do HPS lamps have weaker light output due to their heat expenditure, but the light they produce also won’t be as concentrated as LED grow lights. Due to the HPS lamp’s inefficient design, light waves scatter 360° throughout your grow space, relying on reflectors to redirect a large portion light back down on to the canopy, which inevitably get hot.

By comparison, LEDs commonly focus light at 120° angle from the PCB, directly down onto the canopy and making it easier for plants to absorb all of those photons for photosynthesis.

Thus, your yields will be much higher and more uniform under LEDs than HPS.


Are LEDs Worth The Higher Initial Cost?

Despite all the pros listed above, some growers are hesitant to switch to LEDs because of their higher upfront price. While it’s true many LEDs cost more than HPS lights upfront, they always reward a grower’s wallet in the long term.

Remember: LEDs require less energy to put out the same amount of light as HPS grow lights. For example, a 720w LED can emit the same or more PAR as a 1000w HPS, thus can save more electric bills. Also, since LEDs don’t impart as much heat onto your plants as HPS lights, you won’t have to worry about expenses like AC units, ventilation, or extra irrigation. As a bonus, since LEDs offer direct, full-spectrum light, you will reap higher profits from your higher yields. What’s more, some high-quality LED grow lights have passed DLC certification. In many countries, government subsidies are awarded for using DLC-certified grow lights.


Want To Switch To LED Grow Lights? Remember The Following Tips

If you’re seriously considering switching to LEDs, please remember to re-adjust your irrigation and heating schedules. Since LED grow lights don’t give off as much heat, your plants may initially need less water than HPS, however in turn they may then exceed the watering requirements of HPS as their metabolism builds.

Also, you should carefully monitor the temperature and humidity in your grow room since LEDs won’t give off the same degree of heat as HPS bulbs. Providing you keep these considerations in mind, you should make a smooth transition to lighting your plants with LEDs.

Therefore, replacing HPS with LEDs is an option to save money while reaping more.