LED technology is increasingly being used in sole-source lighting (SSL) for all types of horticultural applications—both in greenhouses and indoor facilities.
Why are growers making the switch from HID to LED?
There are many compelling reasons why growers are making the switch to LED technology, including:
- ENERGY SAVINGS – LEDs use up to 40% less energy than traditional HPS systems to deliver the same light levels.
- OPTICAL DESIGN FREEDOM – LED optics offer exceptional design flexibility in terms of light level, colour spectrum and distribution pattern.
- SPECTRAL TUNING – LED Fixtures offer multiple colour spectral variations. Each specifically designed to elicit the desired plant response. Including leaf size and stem elongation, chlorophyll concentration, pigment concentration, branching and early/late flowering. Plant response times are also often faster with LEDs.
- HEAT MANAGEMENT – Since LED fixtures produce less heat growers can place them closer to the plants –enabling higher light intensities, without excessive heat. Reduced heat also translates into reduced water consumption.
- LONG LIFE, LOW MAINTENANCE – LEDs last much longer than HPS lamps, and require far less maintenance.
From a horticultural perspective, the spectral “tunability” is probably the most unique benefit. So let`s take a closer look at what that means.
The chart below shows a spectral comparison of an HPS lamp vs. 100% red, 85% red/15% blue and 70% red/30% blue LEDs.
As you can see, the HPS lamp delivers the widest range of wavelengths; however, plants and humans perceive light very differently. The human eye responds most strongly to light in the green/yellow part of the spectrum. Plants respond most strongly to the PAR region (blue and red wavelengths) for photoperiodic growth responses and germination control.
Given that much of the light emitted by HPS lamps is not usable to plants—the HPS spectrum is far less efficient. With LED grow lights, the spectral output can be targeted to only those wavelengths that are useful to the plant.
Photosynthesis, flowering, climate response and photomorphogenesis are all affected by the intensity, duration, distribution and spectral quality of light. Since plants respond most strongly to the red and blue wavelengths, with LED-based sole-source lighting (SSL), we can tune the lighting to focus on what the plant uses most.
One of the major challenges in designing LED fixtures for horticultural applications is developing optimum colour efficiencies or “colour recipes” to deliver PAR photons as efficiently as possible and essentially allow growers to “tune” their lighting to the optimal wavelengths for each stage of growth.
For example, if a grower wanted to encourage more compact growth with sturdier leaves, they would use a higher component of blue light. Whereas if the intent is to encourage flowering, the grower would use less blue light and more red light. Similarly, by using specific wavelengths you can manipulate the pigment of the leaves.
In the past, there were no alternatives to HPS. Although we could measure light intensity (quantity), we were not able to measure the effects of specific spectral colour compositions. With the development of LEDs, this is now possible.
The research phase of light spectrum compositions and their effect on plant growth, fruit yield, and quality continues to this day. We are still discovering which crops respond well to LED lighting and to specific spectral recipes. Even certain varietals can react differently to a particular spectral composition.
Many growers remain fairly uneducated about LED technology, especially since some LED manufacturers misrepresent or inflate claims of performance. The general lighting industry saw similar problems during the early years of general area LED fixtures. This lack of industry standards has allowed some less than scrupulous manufacturers to introduce many inferior LED fixtures into the horticultural market which left many growers disillusioned with the technology.
To this day, the most significant roadblock to the widespread adoption of LED lighting is the high cost of ownership.
A good way to get a true comparison between the cost of LED vs. traditional lighting is to look at the cost per µmol delivered, as the outputs from one manufacturer to another can differ. Below is an example to demonstrate:
1000w HPS DE Fixture w/ 2100 µmol output at $550* = $0.26/µmol
215w LED Top Light w/ 550 µmol output at $420* = $1.31/µmol
320w LED Top Light w/ 860 µmol output at $950* = $1.10/µmol
*Pricing is ballpark/MSRP
An incremental cost of four to five times that of HPS, means you have to look at many factors to determine if the ROI on converting to LED makes sense.
Growers should consider not only the initial capital expenditure costs of the luminaires themselves but also the incremental costs associated with a transition to LED lighting. Growers in northern climates, for example, will have to compensate for the loss of heat from the traditional light sources in the winter—so the additional heating costs could negate energy cost savings.
There are undoubtedly many benefits to growing with LEDs. however, converting to LED technology is a BIG investment. So make sure you do your homework in advance.
Use the “LOGIC” checklist to bear in mind when considering a LED lighting system:
Thermal management is essential for maximizing light output, reliability and lifetime of an LED fixture. Passively cooled fixtures are typically better suited for the harsh conditions of indoor growing environments.
Look for fixtures specifically engineered for horticultural applications. Factors to consider include light intensity (μmol/m2/s ), fixture efficiency (µmol/J); light distribution and spectral recipes.
Look out for exaggerated claims. A reputable manufacturer will offer a complete system warranty. Including a rated lifetime of 50,000+ hours and a guaranteed photon flux maintenance under typical operation in a horticultural environment.
Return on Investment
Return on investment for LED lighting is different for every grower. Payback calculations for LED lighting are only useful when they apply specifically to your situation. Look for a manufacturer who will provide a custom light plan that considers all the factors specific to your application.
A good LED lighting system is a big investment, so do your homework. Ensure you are considering all factors when calculating your cost of ownership. The cheapest price may turn out to be an expensive mistake.
What does the future hold for LED technology in horticultural applications? As we learn more about LEDs in relation to horticulture, we will undoubtedly see increasing general adoption as researchers, manufacturers and growers become more educated. And much like the general lighting industry adopted a set of quality standards and benchmarks like the Lighting Facts program, so too will we start to see set standards emerge in the horticultural industry.
The Hybrid Solution
For now, many growers are opting to install hybrid lighting systems i.e. a mix of LED and traditional technologies. This allows them the benefits of both technologies. However, as is the case for any lighting system, a grower should base a hybrid system on a carefully considered light plan that is specific to that particular application. Most reputable lighting manufacturers offer light planning services. Growers, however, should be aware that a company that manufactures only LED or only traditional-source lighting products will, for obvious reasons try to “sell” growers on the technology upon which their products are based. So, working with a manufacturer who offers multiple product technologies will ensure an unbiased recommendation. This allows the grower to know they chose the product/technology that best fits their particular application.
as seen in the October issue of Greenhouse Canada
Lisa Jansen van Rensburg
Lisa Jansen van Rensburg is a Marketing Manager who works with customers, dealers, research partners and the PL Light sales team to not only promote the PL Light Systems’ brand; but also develop new products and tools to ensure that growers receive the best supplemental grow lighting and after-sales support for each individual application.