The commercial horticultural industry has seen significant innovation over the past few years. The growing facilities of today look remarkably different to those considered to be at the cutting edge of design just a decade ago.
The most significant innovations have been in CEA technologies, driven by increasing energy and labour costs. Growers have realized the advantages of investing in equipment and automated systems that will reduce their operating costs (including labour, maintenance and energy-related costs) and increase their bottom line.
As such, energy-efficient supplemental lighting systems are a logical investment for most greenhouse operators. So it’s critical that growers have strategies in place to ensure the optimal performance and ROI of their lighting system, as well as maximizing efficiency and crop yields.
The first, most basic thing you can do to ensure you’re optimizing your lighting is to work with a reputable lighting company to develop a light plan, customized for your specific facility and application, and then install your lights exactly according to that plan.
Light Planning
If you are not familiar with a light plan, it is essentially a calculation of the best possible coordination of luminaires in terms of their distance and orientation from one another, as well as the crop. The trick lies in determining the ideal combination of these factors to ensure that you will achieve optimum light output and distribution, with as few luminaires as possible. The resultant light plan will provide a cumulative overview of the light output and distribution of all the grow lights installed, based on the prescribed mounting positions and orientation.
Reputable lighting manufacturers will guarantee the light levels presented in their light plans, provided the luminaires are installed in accordance with the recommended plan. If you are comparing light plans from multiple lighting suppliers, be sure that the data being presented to you is a true indication of the actual performance you can expect. A new lighting system is a big investment and can significantly impact your yield, so ask questions. Is the proposed light output of the luminaire based on the lamp’s or LEDs’ maintenance factor (“end of life”) for the best indication of actual performance? Does the light plan specify light levels in micromoles vs. lumens or lux? If it’s the latter, they likely are not experienced in horticultural lighting.
Many growers are already familiar with the rule of thumb when it comes to light intensity and plant growth. This rule states that for every 1% increase in PAR light, you will see an equivalent increase in plant growth and yield.
The same principle applies in reverse of course, whereby each 1% loss of PAR light will result in 1% loss in plant growth and yield. So maintaining the highest possible output from your grow lights is critical to maintaining optimal crop yields.
One of the most obvious (but often forgotten) things a grower can do to ensure they are getting the best performance and efficiency from their lights is to properly maintain them. Just like any other equipment, indoor grow lights need to be regularly maintained in order to ensure optimal performance.
Two very simple but critical maintenance measures that every grower using HID lighting should build into a regular maintenance routine are re-lamping and reflector cleaning.
Re-Lamping
It’s a fact that the light output of all luminaires depreciates over time, and this is true for both HID and LED products. HID lamps do, of course, deteriorate faster than LEDs. That said, an HID luminaire can run very efficiently for years and years if it is properly maintained and the lamps are regularly replaced.
For high-pressure sodium lamps, replacement is recommended after 10,000 burning hours to ensure optimal light output. Writing in Produce Grower, Michigan State University extension specialist Roberto Lopez puts the manufacturer-rated life of a double-ended HPS lamp at 10,000 to 15,000 hours to 90% of its initial light output.
Apply the light intensity rule above, where every 1% loss of PAR light can mean a 1% loss in plant growth. Lamp output falls steadily over its burning hours, so an ageing lamp is delivering measurably less PAR to the crop than it did when it was new, and yield follows it down.
This is why regular replacement of lamps is critical to maintaining the optimal PAR light output of your HID luminaires.
Not every grower running HID lighting has a re-lamping strategy in place. Some simply wait until lamps burn out. The better approach is to plan proactively, so that houses, bays, zones or rooms are changed out together and light levels stay consistent across the facility.
Since the size and scope of grow facilities can be very large, group re-lamping can be a very expensive and labor-intensive exercise if you don’t have a well-thought-out strategy in place.
Example
Take a facility with 1,000 luminaires. Replacing every lamp at the same time means buying and fitting 1,000 lamps in a single exercise.
We know the life expectancy of a 1,000-watt DE lamp is 10,000 burning hours. The average use of supplemental lighting per growing season for a tomato or cucumber greenhouse will range from 2,200 to 2,500 hours a year, whereas a cannabis grower would typically run their lights for roughly 4,000 to 4,400 hours a year. Geographic location also affects the number of hours a greenhouse grower needs to use supplemental lighting, based on the amount of natural light available. In an indoor grow, with no natural light and only sole-source artificial lighting, you would need to replace your lamps more frequently.
Typically a lamp will last two to four years, depending on how and where it is used. That means every two to four years you are re-lamping the whole facility to maintain the light levels that produce optimal yields, and that is not a small investment. We have customers with tens of thousands of luminaires in a single facility.
If you had a re-lamping strategy in place, however, you could change a third of the lights out at around 8,000 to 9,000 burning hours (1,000 to 2,000 hours earlier than required), another third at 10,000 hours (at the rated timeframe), and the final third at 11,000 to 12,000 burning hours (1,000 to 2,000 hours beyond the rated life). A vegetable grower doing this spreads the financial impact across roughly a year and a half, rather than carrying the whole facility at once, while still maintaining optimal light intensity.
It’s also a good idea to have a map of your facility and a log capturing your burning hours for each area. This will allow you to plan for staged replacement of lamps and can also provide good insight into how your crop is impacted by reduced light levels.
Installing Your Lamps
It should also be stressed how important it is to ensure your double-ended lamps are installed properly. Most HID luminaires on the market that use double-ended lamps use the same lamp holder brackets. It is incredibly important that the lamp is installed in the correct orientation and that the lamp holders are fully closed when you’re installing the lamp. If they’re not, you will end up with a loose connection which could lead to arcing. Video instructions and PDF instructions are both available in the resources section of our website. Make sure your maintenance crew is trained on how to properly replace the lamps.
When you’re replacing lamps, you should also always confirm the new lamps are compatible with your luminaires to ensure you’re not risking the safety of or damage to lights. You should check the product labels on your luminaires for the lamp types they can accommodate. Ideally, you can purchase your lamps through your light manufacturer to ensure they’re compatible, but you should at least check with them before purchasing new lamps from other suppliers since not all lamps are created equal.
You also want to make sure you don’t have more than 2 on/off cycles for your HID lights within a 24-hour period since this will shorten the life of both the driver and the lamp. This is especially true for the electronic ballasts since repeated re-strikes increase the stress on the high-powered electronic components.
You should also always allow for at least 15 minutes before restarting an HID lamp once you’ve turned it off, to let the gasses in the lamp and the electronic components of the ballast or driver return to room temperature. This will help to maintain the useful life of the lamp.
Cleaning Your Reflectors
Another simple way you can make sure you’re getting the most out of your lighting system is by regularly cleaning your reflectors. Dirt, dust and buildup on a reflector reduce the light that reaches your crop. Michigan State University’s Roberto Lopez estimates that dirty reflectors alone can cut light output by 8 to 15%. If not properly cleaned and maintained, this can mean a loss of quality in your crop, longer crop cycles, and reduced yield. Some lighting manufacturers will tell you that you need to replace your reflectors every year or two. If they’re good quality reflectors, however, made from quality materials, this is not true. You can clean them. The P.L. Light Systems NXT family of HID luminaires is designed so that the reflectors can easily be removed for cleaning, even when the lamp is installed.
To maintain the highest level of performance for your luminaires, we recommend that you check and clean your reflectors every year if possible. Ideally, this should be part of your cyclical maintenance routine and is as easy as removing the reflectors and washing them in a simple 1:100 vinegar and water solution. It is also the guidance we gave Michigan State University when Roberto Lopez surveyed HPS manufacturers on reflector maintenance for Produce Grower. You can check out the resources section of our website to watch a short video on how to do this.
Late spring, as the days are getting longer, is a great time for greenhouse growers to consider cleaning their reflectors, since they won’t be needing supplementary lighting in the greenhouse for a few months. Indoor growers, who use artificial lighting year-round, should include annual cleaning of their reflectors as part of their regular maintenance routine to ensure they continue to deliver optimum performance.
The aluminum material of the reflectors will start to degrade over time as part of normal wear and tear in a greenhouse environment, so at some point you will need to replace them if you want to maintain optimal PAR light output over the long term. The trick is knowing where that tipping point is.
Voltage
Another good practice is to make sure the voltage you have specified for the luminaires matches the voltage you have in your building. This applies to both LEDs and HID. We always recommend speaking with a licensed electrician before deciding what voltage to use to run your grow lights. The voltage will be noted on the product label. A luminaire with a product label stating “120V-240V” will accept any one of these 3 voltages, 120, 208 or 240, and automatically sense the supplied voltage to ensure the same output to the LEDs regardless of the input voltage. A luminaire with a product label stating “277V” will only accept a voltage of 277V.
When it comes to lighting, we typically recommend going with the highest voltage available at your facility, which will also be the most efficient. By using a higher voltage for your application, you can lower driver and conductor losses and increase efficiencies. However, you should always consult with your electrician in advance to ensure you have an adequate power supply for your lighting and other equipment, including HVAC. Your electrician will need to consider your facility’s capacity, conductor sizes, circuit loads and voltage drop.
Retrofitting
Since some horticultural lighting technologies date back more than 40 years, there are some facilities where upgrading the lighting system is really the only way to achieve greater energy efficiencies and maximize light output. Most people will assume that this means upgrading to LED, but that’s not necessarily the case. The most current HID lighting, with electronic ballast and DE lamp technology, is actually highly efficient and can be a very cost-effective way to upgrade from old, magnetic ballast lighting systems.
One of our customers, Burnaby Lake Greenhouses (located in British Columbia, Canada), did just that and achieved very impressive results. They replaced their older magnetic luminaires with the newer high-efficiency 1000W NXT2 electronic alternatives. You can see the full project results here.
Hybrid Lighting vs. LED and HPS Lighting
Another option is a hybrid lighting system, meaning a mix of LED and HPS luminaires, which allows growers the benefits of both technologies.
A hybrid solution provides the flexibility to take advantage of the radiant heat and diffused light of the HPS lighting, but also the energy efficiencies of LED. It also allows greenhouse growers to extend the supplemental lighting period longer into the spring by using only the LED lights when outside temperatures and daylight hours increase. A hybrid system also reduces the initial capex and can allow a grower to further manage costs by maintaining their existing infrastructure.
A hybrid solution can really provide the ideal balance. Comparing light plans for the same greenhouse, planned three ways, shows why. All three plans below cover the same space and target a comparable light level at the crop canopy.
Both layouts reach a comparable average light level at comparable uniformity. The LED plan gets there with fewer luminaires, spaced further apart on the same rows, so it is not asking for more fixtures or additional track than the HPS plan it would replace.
Where the two differ is in how the light travels. The reflector technology in the HPS luminaires helps to diffuse the light by reflecting and refracting photons around the grow area in different directions. This is different from an LED, which directs photons downward. So while both plans target the same light level on the canopy of the crop, you also need to take into consideration how those photons are being distributed into the crop, and what spectrum is reaching the leaf.
That difference is the argument for running both together rather than choosing between them.
The hybrid plan for the same space replaces every other HPS luminaire with two LED luminaires. That spacing means they still mount on the existing truss, rather than needing additional track. It reaches a higher average light level than either single technology plan at the same uniformity, while keeping some of the radiant heat that a greenhouse in a cold climate actually wants.
The hybrid layout carries a smaller increase in up-front cost than going all LED, while still delivering an energy saving against the all HPS plan. So a hybrid solution in many cases really does offer the best balance between performance and efficiency, and could be a good way for someone who has an existing HPS installation to improve their efficiencies, while maintaining the benefits of HPS technology by switching out every other luminaire for LEDs.
Remember that we are looking at the lighting costs alone in these calculations. To really figure out what solution works best for a particular project, we need to also factor in the relevant infrastructure and heating or cooling costs to determine which setup will truly offer the best ROI for each application.
The full comparison these plans come from, including the capital and energy cost side, is available with our cultivation guides.
Frequently Asked Questions
How Often Should HPS Grow Light Lamps Be Replaced?
High-pressure sodium lamps should be replaced after roughly 10,000 burning hours to maintain optimal light output. At typical run hours a lamp reaches the 10,000 hour mark in roughly two to four years. A tomato or cucumber greenhouse typically runs supplemental lighting 2,200 to 2,500 hours a year, while a cannabis grower may run 4,000 to 4,400 hours. An indoor grow with no natural light will go through lamps faster.
What Happens to My Crop Yield If I Leave Lamps in Too Long?
The rule of thumb growers work to is that every 1% loss of PAR light costs roughly 1% of plant growth and crop yield. Lamp output falls away gradually rather than all at once, so a lamp left in too long is quietly costing yield the whole time without ever failing. That is why staged, planned re-lamping beats waiting for lamps to burn out.
Do I Have to Replace My Grow Light Reflectors, or Can I Clean Them?
You can clean them. Some manufacturers will tell you reflectors need replacing every year or two. If they are good quality reflectors made from quality materials, that is not true. Dirt, dust and buildup on a reflector cut your light output, so check and clean them annually. Cleaning is as simple as removing the reflectors and washing them in a 1:100 vinegar and water solution. The reflectors in the P.L. Light Systems NXT family are designed to come out for cleaning even with the lamp installed. Aluminum does degrade with normal wear over the long term, so reflectors do eventually need replacing.
How Long Do I Have to Wait Before Restarting an HID Lamp?
Allow at least 15 minutes before restarting an HID lamp after switching it off, so the gasses in the lamp and the electronic components in the ballast or driver can return to room temperature. You should also avoid more than two on/off cycles in any 24-hour period, since repeated re-strikes stress the driver and shorten the life of both driver and lamp.
What Voltage Should I Run My Grow Lights On?
Generally the highest voltage available at your facility, which will also be the most efficient, because higher voltage lowers driver and conductor losses. Check the product label. A luminaire labelled “120V-240V” will accept 120V, 208V or 240V and will sense the supplied voltage automatically. A luminaire labelled “277V” will only accept 277V. Always confirm with a licensed electrician first, who will look at your facility’s capacity, conductor sizes, circuit loads and voltage drop.
Getting the Most Out of Your Lighting System
No matter what type of lighting system you’re using, there are many ways you can ensure you’re getting the most out of it in terms of efficiency and performance to achieve maximum crop yields.
Each application is unique, so you should discuss your particular situation with a trusted lighting partner to see what strategies and improvements you can make in your operation.
Tell us your crop, structure, and targets. We engineer the rest.
