Are all LED luminaires created equal? 6 things you should know before purchasing an LED system

Jillian Whitehead

Growing Advice, LED luminaires, Lighting Technologies | October 22, 2020

With a flood of LED lighting products now on the market, it can be hard to distinguish what makes for a high quality, dependable horticultural LED system that gets you the results that you are looking for. Unfortunately, not all LED luminaires are created equal, and there are a few things a grower should be on the look for when researching LED luminaire manufacturers.  Doing your due diligence before committing to a lighting installation can save you headaches and money in the long run.  We have worked with countless growers who have installed cheap, inferior-quality lights that begin failing soon after installation P.L. Light Systems is a pioneer in horticultural lighting and has been manufacturing lighting systems for 40 years – so you know we are dependable and that our products are built to last.  There are many reasons growers want to invest in LED lightingincluding increased light and energy efficiency, lower heat loads, improving plant morphology and dimming and daisychaining capabilities.  Let’s take a look at the big picture, so you will know what to look for when purchasing LED luminaires and some of the hidden costs that can sometimes be associated with LED installations.   

1. Is the Luminaire Certified? 

One of the first things you should be doing, is checking to ensure that the luminaires you are purchasing are safety certified.  You should check for CSA certification or UL certification and in some cases checking that it is DLC listedAll reputable horticultural LED lighting companies will have their products rated by recognized bodies for both safety and energy efficiency.  

What is CSA or UL certification?  If a product comes with a CSA or UL sticker, it signifies that it has passed specific safety requirements for use in the intended application. These standards ensure that producthave been rigorously tested to ensure they don’t pose a safety hazard. If a product is CSA or UL listed, it is deemed safe for use when installed in accordance with electrical code requirements.  If a luminaire does not have UL or CSA certification, it would be wise to consider an alternate luminaire, from a reputable manufacturer, that is certified. 

Why is it important to be DLC listed? DLC stands for DesignLights Consortium, and if an LED luminaire has earned certification from them, it indicates a high level of both quality and energy efficiency. The DLC’s stringent standards allow growers to validate and compare the performance of horticultural luminaires―eliminating the need for the thorough vetting and due diligence that you would otherwise be required when considering a lighting system.   

In some cases, lighting products need to be DLC listed as a qualification standard for utility companies issuing rebates. You can check if a product has been DLC listed by going to their website and entering in the company name or product. 

LED-HPS hybrid installation in tomato greenhouse
Hybrid LED and HPS lighting system that takes advantage of both technologies

2. Maintenance and Longevity  

To maintain the optimal performance and lifetime of the LEDs, a luminaire should be designed to drive the LEDs below their maximum wattage. Unfortunately, many lighting manufacturers are “over driving” their LEDs in order to increase the light outputwithout increasing the cost of the luminaire. The problem with this approach, is that by increasing current, you are also increasing heat which accelerates the light degradation and spectral instability of the luminaires. In many designs, the driver also sees a shortened life as it too is subjected to the increased heat of the LED array.  

Ambient temperatures at the top of a greenhouse can be very high and can also lead to a decrease in the efficiency and longevity of your luminaire, so be sure to ask questions about the overall thermal design and heat sinking of the luminaire when purchasing an LED system. Some companies use water or fans to cool their LEDs, which on top of being more expensive to operate, can cause problems such as corrosion and biological growth build up causing increased failure rates.  Companies such as P.L. Light Systems, use passive conduction in their LED luminaires to move heat away from the diodes and circuit boardsresulting in zero corrosion and higher efficiency. Excessive heat can also lead to catastrophic failure of the LEDs, in which case the entire luminaire will have to be replaced (unlike HID luminaires where you can simply replace a lamp).  So working with a well-established company who’s products are designed to last, with local service and support, is a smarter long term investment than purchasing a cheap product from a new manufacturerwhich may need to be replaced every 1-2 years.  

 

3. Energy costs 

LED luminaires use far less energy than traditional horticultural lighting, up to 43% less than an HPS luminairesmaking them an easy choice for growers who may be limited by power consumption or are looking to save money on energy costs. One thing to remember though, is that if you grow heat loving crop such as tomatoes or cannabis, you will need to add extra heat in the winter months to make up for the lack of radiant heat from the luminaires.  This is because LEDs do not have the ability to produce radiant heat like HPS luminaires, and this can mean supplementing with extra heat from natural gas or electricity in the cold months.   

Lighting with HPS luminaires offers the advantage of producing radiant heat which helps to offset the cost of heating the greenhouse, and can mean energy savings for cold climate growersIn addition, the plants benefit greatly from radiant heat since it directly affects leaf temperature.   

However, in cases where the crop requires cool temperatures, such a leafy greens or microgreens, LEDs might be better suited to their growing needs because they keep the crop cooler. Ultimately, a grower should consider all the factors before deciding on one technology vs. another for their application. Given that LED luminaires typically cost up to 4 times as much as HID luminaires, it is critical that one weighs the initial incremental capex costs (including labour and any additional infrastructure like extra track or wiring) vs. the overall impact on annual energy consumption when calculating the ROI.  

Another option that growers should consider is a hybrid installation (combination of LED & HID luminaires) which provides the flexibility to take advantage of the radiant heat from the HID lighting, but also to extend the supplemental lighting period longer into the spring by using the LED lights only 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. 

Lettuce grown under LED luminaires in greenhouse
LED luminaires are well suited to growing cool season crops like lettuce because of the lack of radiant heat

4. Spectrum and Light Recipes 

There has been a lot of talk on light recipes for LED technology, but there has not been much solid evidence to support which combination of wavelengths will be best for plant production, and for the most part, it is largely variety or strain dependent. Regardless of the ratio, broad spectrum (or white) light, which emits all wavelengths including red, blue and green, is being perceived as the best spectral option for sole source lighting applications such as indoor warehouses.  This is because plants can take exactly what they need when they need it. For greenhouse applications, where plants are already receiving full spectrum light from the sun, it is recommended that growers go with a red-blue LED (appearing as purple/pink light), to maximize photosynthesis.  That’s because photosynthesis peaks in the red and blue wavelengths making this spectrum, not only the most efficient for plant growth, but also the most energy efficient.  

So, don’t be misled when a company makes grandiose claims they have developed a light recipe that yields X” results – since it will depend on your growing environment, crop and variety – and as we know yield is highly correlated to light intensity and not necessarily the light quality.   

LED luminaires in tomato greenhouse
You often require more LED luminaires to achieve the same uniformity as one HPS luminaire

5. No one-to-one replacement with HPS luminaires 

LED luminaires are good at shining light directly below the luminaire – in a limited distribution plane – similar to a “spotlight.”  When readings for LED luminaires are taken or used in marketing, they usually only tell you the light reading from directly below the light.  This is because LEDs lack the optical reflector technology that HID luminaires have and are therefore, less efficient at distributing light.  So, the further you get from directly beneath the light source in either direction, the lower the value of the light reading.  HID luminaires use reflectors to dissipate light and create a uniform light distribution over the crop.  HID luminaires can therefore be spaced further apart resulting in fewer luminaires needed to achieve uniform light levels consistently across the canopy.  LEDs on the other hand, will need to be spaced closer together so the light can be distributed uniformly over the crop and light levels can remain consistent – often 2-3 LEDs are needed to replace one HPS luminaire. So even if a company claims that the light output of an LED luminaire is the same or better than an HPS, you will still need more LED luminaires to create the same light uniformity over the crop. 

 

6. Are the LEDs actually made for plants? 

Some lighting companies who produce and sell lighting for homes, office, or other business applications have also tried to capture the horticultural market by claiming to produce horticultural lighting.  If the company does not already have a history and reputation in the horticulture sector, be sure to do your homework.  Many of these companies sell horticultural lighting at cheaper prices because they have been built with cheap parts and LED diodes not made for plant growth.  In fact, we often come into many greenhouses/warehouses who have bought cheap lighting products that fail or don’t produce results 

So before investing money into an expensive lighting system, be certain that the light emitted is in the PAR range. Make sure any claims of intensity and efficiency can be validated – the best way to do this is to check if the product is listed on the DLC’sQualified Product List database (QPL). Also make sure the company understandthe goals of your horticultural business.  Do some background searches, see who they have worked with in the past and get other growers opinions on the products.  

One last point to question to ask, is can you depend on your lighting manufacturer?”.  Many lighting companies, especially newer ones, build their products off-shore and ship them in.  In times such as the pandemic, many customers have been unable to get their orders delivered, secure replacement parts or reach customer service.  At P.L. Light Systems we are in North America and build and manufacture our lights here too – so we always have a steady supply of inventory for customers when they need it and a local customer service and sales team available for support.