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Why Upgrade From HPS to LED?

Why upgrade from HPS to LED grow lighting?

High Pressure Sodium (HPS) grow lights are cheap to buy and proven to work. Many growers have grown reliably for a long time with a combination of Metal Halide, High Pressure Sodium and Ceramic metal halide grow lights.

What is HPS Lighting?
High Pressure Sodium Lights, commonly referred to as HPS lights or High Intensity Discharge (HID) lights, belong to the category of gas-discharge lighting. HPS lights emit light in the orange-red part of the spectrum, which is rich in the wavelengths that plants use for photosynthesis.

What is LED Lighting?

LED (Light Emitting Diode) lights for plants are lighting systems specifically designed to provide the necessary wavelengths of light required for photosynthesis.

Growers gain experience of the best growing techniques, strains and environmental controls with HID grow light systems. Upgrading to LED grow lights will mean change to some of these practices and will require adjustment to established ways of working.

However the argument to upgrade to LED has become very convincing due to recent dramatic increases in electricity costs, a reduction in the cost of purchasing LED grow lights and increased LED grow light performance .

LED grow lights vs HID grow light efficiency comparison

For comparison purposes we reference an optimised HPS system with the following specification:
  • Digital ballast (95% efficient)
  • High PAR bulb (Sunmaster, Grow+ Photonic)
  • High quality reflector (Adjust a wing Defender, medium size)
  • An enclosed environment and highly reflective walls (silver mylar)

The efficiency of this system is 1.3 µmols/watt PPFD (photosynthetic photon flux density). This means for every watt of energy consumed 1.3 µmols of PAR light will reach the plant canopy. 

What is PAR Light?
PAR (Photosynthetically Active Radiation) lights are specialised artificial lighting sources designed to emit wavelengths within the photosynthetically active range.

Todays LED grow lights are almost twice as efficient at delivering PAR to the plant canopy. 

High pressure sodium and metal halide vs LED grow light efficiency comparison

Comparison of HID and LED grow light costs

Even though the purchase cost of LED grow lights has reduced dramatically in the last few years you still have to pay three or four times as much for a highly efficient LED grow light system than an efficient HPS system.

However, by saving 48% on electricity and no replacement bulbs costs you will get payback in less than 1 year. After that you are saving every further year you grow.

Below is a cost comparison of delivering an average PAR intensity of 800µmols/m²/second in a 5ft x 5ft or 1.5m x 1.5m grow area.

To deliver this average PAR level you would need:

750 watts of high efficiency LED grow light, running cost $846 per year in electricity ( 14hrs/day @ 23c/Kw hour)

1400 watts of HPS grow light, running cost $1,627 per year in electricity (14hrs/day @ 23c/Kw hour)

The cost of the HPS fixture is $100 and the 750 watt LED grow light is $700

Comparison of running cost of HPS grow lights and LED grow lights

Double your yield in grams per watt

If you weigh your yield of dry herbs and divide by the grow lighting systems power consumed (per hour) you get a number in grams per watt. This number is the best way to benchmark how efficient a grow light system is.

Typically the yield from a HPS system will be 0.4 to 0.5 grams per watt. A typical 600W HPS system yield is 640 watts x 0.4grams = 240 grams per grow cycle.

With a highly efficient LED system you can double the yield per watt.

Grow much more in the same space with LED grow lights

AS LED grow lights run cooler and more efficiently you can push performance in your grow area further with LED grow lights than HPS grow light systems

For example a 1,000 watt double ended 400v Gavita High Pressure Sodium grow light in a 5ft x 5ft tent will deliver about 650µmols/m²/second.

A 750watt LED grow light in a 5ft x5ft tent will deliver an average PAR intensity of about 800 µmols/m²/second.

This is a 23% increase in average PAR intensity which will translate directly into a 23% yield increase with 30% less power consumption.

LED provides the best growing spectrum for short and dense growth

The HPS grow light spectrum is mostly red and green. Red is good for flowering and green is excellent at penetrating the canopy. However there is only a small output of blue wavelengths at 3 to 4%, even in the ''dual spectrum' HPS bulb tested.

This is why growers traditional use Metal Halide bulbs in the vegging stage and why plants will be prone to stretching when switching to HPS for flowering.

10-15% blue is necessary to keep the plant growth dense and LED grow lights emit this proportion of blue light in their grow light spectrum output.

LED grow lights can be used at all stages of growth and do not need changing from the vegetative to the flowering stage.

Metal Halide, High Pressure Sodium, Ceramic Metal Halide and LED grow light spectrum comparison

Reduce power consumption by 40% and reduce heat output by switching from HID to LED grow lighting

Modern LED grow lights are twice as efficient as an optimised HPS system and achieve much better efficiency which means you can reduce electricity consumption by up to 50% and still get the same yield.

Upgrade from HPS grow lights to LED grow lights and reduce Heat output by 60%

Grow tent temperature difference between a tent with a HID grow light and a tent with an LED grow light

If your grow light system is inefficient it will produce less light and more heat. The additional heat leads requires more ventilation to remove it and can stress and damage plants. In the worst case you may have to stop growing during hot spells or use air conditioning.

LED grow lights produce 60% less heat than the equivalent HPS grow light system. Your plants will be less stressed in warm weather and your fans will run slower and quieter.

LED grow lights are safer than HID grow lights

Voltage in the grow room

A HPS Bulb is started with the ballast with a voltage between 2500 and 4000 Volts. This is necessary to spark across the gap in the tube and illuminate the gas inside. The voltage then adjusts to the normal operating voltage of the HPS bulb at around 230 Volts.

LED technology has no requirement for a startup voltage and LED grow lights will run at less than 100Vdc in the grow room, often as low as 24Vdc. A low and safe voltage to have in the grow room around water and plants.

Water protection

It is not possible to insulate the HPS bulb against water splashes as the bulb screws into an open terminal which it is not possible to seal. The requirement to have air circulating and cooling the bulb means it is not possible to seal the HPS fitting against water ingress.

High quality LED grow lights are completely water sealed to Ingress Protection (I.P.) rating of 66 which means you can splash water on it without any risk of electrical faults.

LED Grow light surface temperature is much lower than HPS grow lights

The surface temperature of the 600W HPS bulb tested with our thermal imaging camera was in excess of 330 Degrees Celcius or 626 Fahrenheit (the thermal camera range ends at 330 Degrees Celcius so the actual temperature is higher).

LED grow light surface temperatures are much lower than HID grow lights making them safer to use as the risk of fire is greatly reduced

Modern LED grow lights are passively cooled and highly efficient so the surface temperature of the light is very low. The normal operating surface temperature of an LED grow light is as low as 40 Degrees Celcius or 104 Degrees Fahrenheit and the LED grow light is comfortable to touch and have close to plants without any safety risk.

LED grow lights better for the environment than HID grow lights

A HPS Bulb contains mercury which must be disposed of in a controlled way as it is highly poisonous to the environment. Bulb changes every few grow cycles results in a lot of toxic waste to the environment overt he course of a growers life. Switch to LED and your light fixture will not have to be replaced for at least 50,000 hours (8.5 years @16 hours/day) and no harmful substances to be disposed of.

Last, but not least, Laziness

Have you heard the expression 'efficiency is intelligent laziness'? I love this phrase and it's perfectly apt for the LED vs HPS debate because:

LEDs require no bulb change, it's a drag to need two bulbs for each grow and having to change every few grows. Modern LED grow lights output 80% of their original output for 50,000 hours (8.5 years at 16h/day). . With an LED system like the MIGRO ARAY 

You get even coverage across your grow. No more handling different water requirements for the plants in the centre vs the edges of the grow. The plants will love it, especially the plants at the edges.

LED grows require less heat removal. Less stressing about temperatures getting too high and noisy fans running at full speed.

Summary: The benefits of LED lights compared to HPS lights

- Recent reductions in LED costs
- Improved efficiency and performance with LED lights
- Electricity savings
- No bulb replacements costs / LED lights are water sealed
- Improved yield because of better than average PAR intensity
- LED lights run cooler; less ventilation necessary
- Better spectrum for plant growth & even coverage across the grow area
- LED lights are safer because of lower voltage and better water protection
- LED lights contain no mercury & generate less waste
- LED lights & fixtures last longer


1 thought on “Why Upgrade From HPS to LED?


Great article. The problem with changing to LED lighting is not just the factors listed above. The issue is learning how to utilize the new hardware. When first using a HPS system it took time to calculate things like the optimum height the light needs to be placed above the canopy, how that effected nutrient usage, even the daily weather could effect an indoor setup. The new setup could potentially take three to four growing cycles to perfect. So starting off with LED may be the better option but swapping from HPS to LED is not just a simple matter of swapping out the lighting system. So if you are starting out choose your lighting system carefully as changing over is not as simple as people may assume.

April 9, 2024 at 11:49am

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