Light with the optimal intensity and wavelengths grows better-tasting basil.

Light with the optimal intensity and wavelengths grows better-tasting basil.

Chlorophyll gives plants their green colour, while at the same time playing the central role in life-giving photosynthesis. The chlorophyll molecule helps to capture sunlight and transfer energy, enabling plants to produce the carbohydrates and oxygen they need for growth. But the quality of light received by a plant can have a dramatic impact on the highly complex process of photosynthesis. For example, morning sun is skewed towards the blue end of the visible light spectrum, which signals plants to open their microscopic stomata, admitting carbon dioxide used during the day for photosynthesis.

As part of her Ph.D. studies, Sylvain Dubé examined in detail how the ultraviolet radiation in sunlight affects photosynthesis and other plant processes. The research showed that selecting precisely the right balance of wavelengths and luminous intensity makes plants healthier and improves growth, and that brightness and wavelength affect various light receptors in the plant. The result of this may be that the plant produces special metabolites, molecules that can produce flavours or scents. This is of particular interest to growers of herbs and spices such as basil and dill.

But how do we produce the right sort of light, in the right amounts and without wasting energy? The “Smart Light System” from the Swedish company Heliospectra is an intelligent lighting system for use in greenhouses. Founded by Sylvain Dubé, the company took its name from Helios, the Greek sun god, combined with the plural form of spectrum, a Latin term adopted in the science of optics to describe the various wavelengths of electromagnetic radiation.

Smart Light System

The technology is based on a system of lamps, sensors, and computer software. The lamps consist of High Brightness LEDs, or HB-LEDs, which can be precisely controlled to generate light with optimal intensity and wavelengths to promote healthy plants. Sensors are placed beneath the light source to register the plants’ physiological conditions, which in turn regulates the light through a computerised knowledge bank.

The computer software makes continuous decisions to adapt to the needs of the plants. The Smart Light System grows stronger plants that are better able to resist pests and disease. Tests have shown that plant growth rates can be increased by at least 15 percent.

Lower energy consumption

Modern greenhouses use High Pressure Sodium (HPS) lamps, which provide strong light but also consume large amounts of energy. Only about a quarter of the light from an HPS bulb goes toward plant photosynthesis, with the rest lost in the form of heat and wavelengths of light that plants cannot use. And HPS lamps, which contain mercury, must be replaced every three years. The HB-LEDs used in the Heliospectra system are more energy-efficient, last longer and contain no heavy metals.

Tests have shown that up to 50 percent of the energy consumed in today’s greenhouses can be saved with LED lighting. Heliospectra estimates that energy consumption could be reduced by 45 GWh per year in Sweden and 75 TWh per year in Europe if the greenhouse industry were to substitute HB-LED for conventional lighting. Diode lighting is also more versatile, since hundreds of small light-emitting diodes can be assembled in a large unit, giving plants precisely the light they need.

However, there are a number of problems with LEDs yet to be resolved, most prominently their higher cost. But with development moving forward rapidly, prices are expected to fall.

Green vision

Another potential environmental benefit arises with reduced transportation. A large share of the fresh produce eaten in northern Europe is grown in the south and trucked long distances to market. Everyone living up north is of course happy not to be limited to beets and turnips for half the year, which is well and good, but the system is a substantial energy consumer. Also, vegetables grown for shipment northward are usually harvested early, when the taste is less than optimal.

LEDs cost more, but they use less energy.

LEDs cost more, but they use less energy.

Sylvain Dubé says that greenhouse agriculture powered by LED technology greatly extends the season for vegetable production in the north, reducing long-distance transportation and improving taste and nutritional value. But this vision is still awaiting improvements in energy efficiency for LEDs.

Many potential applications

Santa Maria, a company in the business of growing and selling herbs, is interested in this green lighting technology, and has set up a pilot project with 200 lamps in greenhouses. This idea is to evaluate whether the concept is feasible in greenhouses in Sweden and Holland, countries with high energy prices.

If the pilot project pans out and LED technology continues to develop, Heliospectra sees a gigantic market. The lighting system can be used not only in greenhouses to grow a wide range of vegetables, but also for production of other types of garden plants. The right light in the right quantity and quality is also important in preparing seedlings for re-forestation. And the company sees applications in light therapy and the cosmetics industry.

Article published in April 2009