As demand for more efficient and effective lighting fixtures rises, lighting manufacturers continue to develop the latest and greatest in horticultural lighting. Although many advancements have been made with high intensity discharge (HID) lighting, such as the availability of more efficient digital ballasts and enhanced spectrum bulbs, other types of innovative lighting technologies are quickly taking center stage in the indoor gardening community. Both light-emitting diodes (LEDs) and induction lighting systems are rising in popularity among growers looking for high efficiency. Aside from coming a long way individually, these technologies are being used together and their combination is quickly changing the way we view artificial horticultural lighting.

LEDs

The first generation of horticultural LEDs fell short of meeting the rigorous demands of the indoor gardener and were a disappointment to say the least. Fortunately, LED enthusiasts did not stop developing innovative products and over the last few years, horticultural LEDs have evolved into practical horticultural lighting solutions. Most of the advancements in LED lighting can be attributed to our ever-expanding understanding of plant physiology and manufacturers producing higher-wattage diodes.

The more we understand how plants use particular wavelengths of light and which individual wavelengths are best used in combination with each other for achieving optimal growth, the more LED grow lights continue to improve and become instrumental for indoor growers. After all, the customizable spectral output is one of the biggest reasons why LEDs are so unique.

An increasing number of manufacturers is also playing a large role in the practicality of horticultural LEDs. These systems exploded in popularity in all realms of lighting applications because of their high energy efficiency. This means more manufacturers are committed to producing high-quality LEDs. The horticultural industry reaps the rewards of the research and development performed by these companies.

A few years ago, 3- or 5-W diodes for horticultural LEDs were virtually unobtainable due to the high cost of production. As costs decreased on these higher-wattage diodes, horticultural LED manufacturers were able to integrate them into their fixtures. The higher-wattage diodes give new horticultural LEDs the ability to penetrate into the plant canopy in a manner comparable to HID lighting fixtures—an attribute non-existent in the first generation.

Induction Lighting

Many years ago, Nikola Tesla patented wireless transfer of power to electrode-less lamps and the concept of induction lighting was invented. Although Tesla may not have intended for his invention to be one of the most effective lighting sources for indoor horticulture, this has become the case. Induction lighting uses a magnetron that excites gases and metals within a sealed bulb, which in turn produces light. A sealed bulb means there are no protruding electrodes—the biggest contributor to the degradation of most artificial lighting sources.

Most horticultural bulbs need replacement annually, but induction lighting lasts longer and runs more consistently than other systems. Induction lighting systems will not lose photosynthetically active radiation (PAR) values over the course of a growing cycle. In fact, induction lighting technologies can hold their PAR value for multiple years, which can provide the grower with consistent results cycle after cycle. Currently, there are two types of induction lighting systems used for indoor horticulture: induction fluorescents and sulfur plasma.

Induction fluorescents – Induction fluorescents differ from regular horticultural fluorescents in a few ways. As previously mentioned, induction lighting requires no electrodes. Have you ever noticed the area closest to the electrodes turns dark brown or black as regular fluorescents age? This is because the electrodes protruding into the bulb cause the internal components to leak or burn off, which means the bulb loses its effectiveness (PAR).

This depreciation in PAR is the reason fluorescent bulbs must be replaced annually for horticultural purposes. Because induction fluorescents have no electrodes, they can retain a consistent light output for upwards of 10 years. In fact, even plants that have higher lighting requirements can be grown using induction fluorescents for five to seven years before there is a noticeable reduction in PAR.

Sulfur Plasma – Sulfur plasma lamps use a small, fused quartz sphere that contains sulfur and argon gas. Sulfur plasma lamps use radio frequencies to excite the sulfur and argon, causing them to illuminate. This is similar to the way the sun produces light. Therefore, sulfur plasma lighting is able to produce a spectral output close to that of sunlight. In fact, the color rendition index (CRI) and correlated color temperature (CCT) of sulfur plasma lighting are the closest to sunlight of any artificial light source.

As with induction fluorescents, the unique induction design means the PAR output will degrade slowly. Longevity combined with superior spectral output are what make sulfur plasmas one of the most sought after horticultural lighting systems available. Like LEDs, as more companies start to produce sulfur plasma lighting systems, the technology will get even better and the price will eventually start to drop. A sulfur plasma lighting system will quickly pay for itself through accrued energy savings.

Combining Different Lighting Technologies Inside Your Growroom

The most innovative lighting systems currently available are probably not based on a single technology but on a combination of technologies. Lighting fixtures that combine HID lighting along with LEDs have been available for some time, and more recently, induction light manufacturers (both fluorescent and sulfur plasma) have been using LEDs to make their lighting systems the best in the business.

The most commonly used LEDs in these combined technology systems are the red-spectrum LEDs. Deep red-spectrum LEDs (620 to 660 nm) are used in combination with induction fluorescents and plasma sulfur lighting to provide the ideal spectrum for chlorophyll B’s peak absorption. This leads to more bountiful flower sites and larger flower sets. Considering both induction technologies provide amazing full spectrum lighting with high CRI ratings, the addition of red-spectrum LEDs is specifically aimed at creating larger and more prolific blooms. Induction lighting systems combined with high-wattage red-spectrum LEDs are, in my opinion, the ultimate horticultural light source when it comes to efficiency and effectiveness.

Staying in the Red

Some manufacturers of induction lighting systems have taken light manipulation of photosensitive plants to a whole new level with the use of other red-spectrum LEDs. Our evolving understanding of plant physiology has recently discovered that particular wavelengths in the red spectrum are responsible for triggering the flowering response in plants. In nature, this far-red spectrum is present right as the sun is setting.

It is this particular spectrum produced at sunset that allows photosensitive plants to enter a fruiting or flowering period even when the dark period is far less than 12 hours in duration. This is why outdoor plants, even photosensitive ones, will begin flowering long before the equinox. However, in a typical indoor garden the light spectrum doesn’t change as the lights turn off. Instead, it is an all-or-nothing situation where the entire light spectrum provided to plants is instantly turned to darkness as the lights are switched off by the light timer.

Many growers are not aware that the actual triggering of flowering occurs during the dark cycle, not while the lights are on. This is why traditional lighting cycles are based on a 12-hours-on and 12-hours-off photoperiod. Photosensitive plants grown indoors require at least 12 hours of darkness to properly trigger their flowering response and to produce bountiful flowers.

Innovative horticultural lighting manufacturers, particularly those producing induction technologies, are now integrating 720 to 740 nm LEDs that come on at the end of the light cycle. The added 720 to 740 nm spectrum produced by these LEDs simulates the spectrum produced by the sun at sunset and triggers the flowering response more quickly. The simulated sunset spectrum allows plants to relax more quickly when entering the dark cycle.

Plants grown under traditional lighting cycles can take up to three hours to relax into a state where they begin the flowering response while plants provided with the 720 to 740 nm spectrum at the end of the light cycle will act more like plants grown outdoors. The biggest advantage of lighting systems that use the 720 to 740 nm LEDs is that they allow the grower to increase the lights-on duration by an hour or two. This provides more energy to the plants and helps them produce larger and more prolific flower sets.

Take-home Message

The more we learn about how particular wavelengths of light affect the way plants grow, the larger the role lighting sources like LEDs will play in indoor horticulture. Cutting-edge horticultural lighting systems such as induction fluorescents and sulfur plasma systems are exactly what the indoor horticulture community needs to continue moving forward.

Combining induction technologies with particular wavelengths produced by LEDs is a way to integrate the best of both worlds: full-spectrum lighting with a focus on high-energy blooming spectrums.

This combination will help meet the strenuous demands of the indoor garden and will allow growers to better mimic the way plants respond to natural light.

As new technologies are developed and existing technologies are refined, a combination of multiple innovative technologies will likely be the answer to providing gardeners with an optimized lighting system.