In a world where burgeoning populations require sustainable crop production, the need for efficient lighting systems for horticulture is even greater. To get a better grasp of what the future holds, it’s helpful to take a look at how far things have come.
Lighting is the biggest single cost for indoor growers, and today’s grower faces a daunting array of choices, requiring considerable knowledge to gain a competitive advantage. Fluorescent lights produce the most energy per watt, but LEDs use the least energy and last longer, while high-density lamps remain the workhorses many growers rely on despite their energy demand and high operating temperatures.
Today’s growers face a dizzying range of choices as energy prices rise. The road leading to where growers are today goes back more than a century to the late 1800s, when prominent scientists such as Thomas Edison and Nikola Tesla raced to develop the first light bulb. Edison’s incandescent light bulb became commonplace around the world, but a century later engineers are turning to Tesla’s invention—the plasma lamp—for high-powered, high-efficiency lighting that mimics sunlight.
Standard incandescent bulbs simply do not produce sufficient light for commercial growing, but the jury is still out over which of the four commercially viable systems are best: high-intensity discharge (HID), fluorescent lighting in all its shapes and forms, light-emitting diodes (LEDs) or the plasma lamp. Each has advantages and disadvantages.
History of Fluorescents
In the 1880s, scientists began looking for ways to create light by tapping into the luminescence created when an electric current passes through mercury vapor inside a glass tube. They found that nearly invisible ultraviolet light can be made to light a room by painting phosphor inside the tube.
Thomas Edison abandoned the idea in favor of the simpler, though less efficient incandescent light, but his employee, Daniel Machfarlan Moore, persevered and found a way to improve these “fluorescent” bulbs to generate light closer to natural daylight. In 1912, General Electric bought the patent but it was 1938 before a consumer product become available. The lamps lose a little energy as heat, but roughly 85% of input energy becomes ultraviolet and visible light.
In the 1970s, special fluorescent tubes designed to provide a range of light color suitable for growing became popular, and demand for them rose. Their benefits include low power consumption, long life and high efficiency. They range from 50 to 100 lumens per watt—several times the efficiency of incandescent lights. One disadvantage is that their mercury content means growers need a method of safely disposing spent bulbs.
Experiments using artificial light to grow plants started as early as 1861. Twenty years later most early adopters were using the high-intensity light of carbon-arc lamps to supplement natural light in greenhouses. Problems included a need to replace carbon lamps often, and dangerous ultraviolet light. General Electric’s incandescent Mazda bulb could last 3,000 hours and became the lamp of choice for horticultural research in the 1920s and ’30s. By then, testing had started on low-pressure mercury vapor lamps, and soon researchers realized the potential of sodium lamps for plant lighting.
The 1930s brought the longer-lasting, more efficient fluorescent tubes, which produced a broader spectrum of light. The addiction of new phosphors led to more efficiencies and the ability to change the spectrum to better suit plant growth. Further testing led to the development of high-pressure mercury lamps in the ’30s followed by metal halide and high-pressure sodium lamps through the ’50s and ’60s.
These lamps were highly efficient, lasted a long time and provided a relatively broad spectrum light for a wide range of plant species. They remain the lamps of choice for supplementing naturally lit greenhouses. HID lighting has been the workhorse of commercial indoor growers for several decades.
Several varieties of HID lighting exist. Metal halide daylight bulbs emit light in the blue range at about 5,500˚Kelvin, similar to spring outdoor light. They’re good for plants at earlier stages of development. A warmer lamp, metal halide is more yellow at 3,200˚K.
The newer, ceramic discharge metal-halide lamp, also called ceramic metal halide (CMH) or light-emitting ceramic, is 10 to 20% more efficient than the traditional quartz metal halide with better color rendition. High-pressure sodium lamps are more efficient than metal halide and because they produce more light in the red part of the spectrum, they’re considered ideal for blooming.
The bulbs are preferred in greenhouses where sufficient blue light is available, but northern growers may find they attract pests, and a yellow bias in their light can make it difficult to monitor plant health without the use of protective growroom glasses. HID lamps give good results, and while initial set-up costs are low, they add up over time due to bulb replacement and high energy use.
The first patent for an LED lamp was issued to Texas Instruments engineers James R. Biard and Gary Pittman in 1961, after an accidental discovery while working to develop the semiconductors that became today’s microchips. A year later, the SNX-100 sold for $130. It produced invisible infrared and was used in punch card readers on early IBM computers. The following year General Electric produced the first visible-light light-emitting diode.
A high-brightness LED appeared around 1976. Early uses were indicator lamps on instrument panels and meters on specialized equipment, then in consumer electronics. In 1990, researchers began testing LEDs for plant growth at the University of Wisconsin. A commercial production technique for high-brightness LEDs was demonstrated in 2012.
Today’s LEDs light flat-screen television sets and homes while also being used in horticulture. New phosphors are improving the color range of the newer, high-intensity LED grow lights. Once only able to generate red light, LEDs can now produce a range of colors. That, and their high efficiency and longevity have attracted a lot of growers to LED lights.
LEDs can deliver 18-22 lumens per watt versus incandescent bulbs rated at 15 lumens per watt for a 60-100-W bulb. Fluorescent are the most efficient at 100 lumens per watt, but the gap is narrowing. Just like microchips, LEDs follow Moore’s Law, which means every new generation is twice as efficient as the previous, roughly every 18 months. LED bulbs are rated to last 50,000 hours—enough for more than 10 years of service.
Light-emitting plasma (LEP), a.k.a. magnetic induction lamps, also hold a lot of promise for indoor growers. In its simplest terms, plasma is the same energy that produces light in the sun and other stars.
It’s one of the four states of matter, along with solid, liquid and gas. By putting gas molecules in a high-energy state using extreme heat, laser or an electrical field, it excites the gas into a plasma state, which generates streams of photons, or brilliant, bright light.
Inventor Nikola Tesla demonstrated artificial plasma light in 1894, but Thomas Edison’s much simpler incandescent bulb became the standard for general purpose lighting. Yet plasma is far more efficient and the bulbs last much longer, and in the 1960s General Electric developed a plasma lamp for stadium lighting.
In the 1990s, the sulphur plasma bulb was put into production. A fused quartz bulb containing sulphur powder and argon gas, lit with a magnetron using microwave energy, it was only available in high-wattage bulbs. Problems included radio interference from the bulbs and growers found the light quality unsatisfactory.
Microchips generate the electromagnetic energy used in many of today’s plasma lamps. Plasma bulbs are efficient like LEDs, plus they generate light in a wide spectrum similar to sunlight. Without the metal filament used in high-intensity discharge lights, some plasma bulbs can last 50,000 hours before significant degradation affects light output.
Inside an LEP bulb a stream of concentrated radio waves bombards a small, gas-filled quartz bulb to create a bright light similar to HIDs, without all the heat. Some use half the energy of a conventional lamp for the same growing area. Plasma lights also provide the same ultraviolet benefits of sunlight for protection against pathogens such as powdery mildew.
Like LEDs, cooler temperatures allow LEP bulbs to be placed closer to the foliage. Output is concentrated in the spectrum of photosynthesis, rather than in heat-producing red and infrared bands, and cooler bulbs can be placed closer to the plants, without the need for fans or cooling.
But because they lack the red spectrum plants need to bloom, many growers use supplemental lighting, especially HPS, for that stage of growth. LEP systems can be costly, so buyers should do their homework. In any lighting systems, growers should check the unit’s light spectrum, ask whether the bulb is fixed or replaceable, and find out about bulb life and degradation.
Modern developments mean it’s an exciting time for indoor growers. New technology including LED and plasma will continue to evolve and get better, and no doubt new developments will improve more established, competing technology. Anyone considering jumping into indoor growing, or looking to upgrade their growrooms, should do their research and cross-check manufacturers’ claims.
Proven, established lighting systems will provide good yields at a lower start-up cost, but those in it for the long haul should consider all the costs and benefits of the emerging technologies before investing.