How LEDs Work

LEDs create illumination by the movement of electrons in a semiconductor material. LEDs are solid-state devices, which makes them virtually indestructible in relation to other types of lighting technologies. Containing no filament, moving parts or pressurized gas prolongs LEDs’ longevity. In fact, LEDs that are used for horticultural purposes can last five-to-ten years.

LEDs have lenses on each bulb, so there is no need for a reflector. This can make determining the proper light footprint rather difficult.

LED longevity dwarfs the current HID and fluorescents’ expected light hours for plant growth. The color rendition of HID and fluorescents will actually change over time as the composition in the arc tube or gas chamber breaks down, leaving a spectral output that is undesirable for plant growth. The decline in spectral output of LEDs is insignificant even over a five-to-ten year period.

Using LED as Supplemental Lighting

LEDs designed to boost the amount of red light in a garden’s fruiting/flowering room will promote larger fruit and flowers and heighten the ripening response in photosensitive plants. A 10-watt cluster LED light containing 10 to 20 bulbs that only emit one specific color of the lighting spectrum is suitable for supplemental purposes.

Another single-spectrum application that is growing in popularity is using ultraviolet LEDs, which emit UV-B. Ultraviolet light is almost nonexistent in indoor gardens that use only HID. Many growers are enhancing essential-oil production and promoting stronger structural integrity in their plants with the use of UV-B-emitting LEDs.

Using LED as Primary Lighting

LED manufacturers have come a long way in producing lighting fixtures capable of replacing HID or fluorescents as the primary lighting source for an indoor garden. In the past, LED grow lights used for primary lighting created spindly plants unable to produce large fruit or flower sets because the LEDs used were not powerful enough to penetrate the plant canopy. The most recent horticultural LED fixtures utilize high wattage (2- or 3-watt bulbs) to enhance light penetration.

Air circulation within an indoor garden is extremely important, especially in gardens using LEDs as the primary lighting source.

The use of higher-wattage LEDs creates a higher concentration of light from a single focal point, allowing usable light to travel further. LED panel lights designed for primary lighting not only use high-wattage LEDs, they also utilize multiple wavelengths of colors specific to photosynthesis.

Initial Cost

The best way to do an initial cost analysis for LED fixtures is to convert the cost of the unit into a dollar-per-watt ratio. For example, an LED light fixture that costs $800 and draws 400 watts would have a cost analysis of $2 per watt. You will find units ranging from $1 per watt up to $5 per watt. On the basis of cost analysis alone, the more watts per dollar, the better. This is assuming you are comparing light fixtures with similar spectral outputs so color rendition can be taken out of the equation.

Placement in the Garden

There is no ballast required with LED lights. Instead, there is a circuit board within the fixture’s main housing. This can make some LED light fixtures rather heavy. Make sure your eye bolts are anchored and the material you use to hang your light fixture can handle the weight. I recommend chain.

LEDs have lenses on each bulb, so there is no need for a reflector. This can make determining the proper light footprint rather difficult. Generally speaking, LEDs designed for use as a primary light source should be hung 18 to 24 inches above the top of the plant canopy. Always check with the manufacturer because some LED units may have different angled lenses and suggest a particular way to hang them.

Adding Heat to an LED Grow Room

LED lighting fixtures produce much less radiant heat than HID lighting fixtures. This may require a grower to heat the room or, more specifically, the root zone of plants. In standard HID gardens, the radiant heat keeps the root zone warm, a condition that fast-growing annuals find favorable. By supplementing heat to the root zone in an LED garden, a grower can increase production by up to 20%. Soil cables or heat mats are great ways to heat the root zone of plants.

Additional Air Movement

Just like the wind outdoors, air movement indoors directly influences the structural integrity of plants. Ample air movement strengthens stalks and creates robust branches, which promote and support heavy fruits or flowers. Sufficient air movement also creates uniformity of the atmospheric conditions within the garden, i.e. humidity and temperature.

Air circulation within an indoor garden is extremely important, especially in gardens using LEDs as the primary lighting source. Using oscillating fans is probably the best way to ensure sufficient air movement between plants.

Metabolic Stimulators

Another way to maximize performance in an LED grow room is by supplementing metabolic stimulators. Metabolic stimulators increase the rate at which plant functions occur, which increases growth rates and yields. Advanced Nutrients’ Nirvana and Bio-Bizz’s Bio-Heaven are both quality metabolic stimulators for use in soil. For hydroponic gardens, Advanced Nutrients’ Bud Ignitor would be my recommended metabolic stimulator. LED light fixtures produce a high amount of PAR (photosynthetically active radiation). The use of metabolic stimulators in an LED garden helps the plants process as much of that PAR as possible.

LED horticultural lighting units are a relatively new technology in a state of constant evolution. Before purchasing any substantial piece of equipment for your indoor garden, it is a good idea to research and compare. Love them or hate them, LEDs are here to stay. As our knowledge in plant physiology expands and the need for more energy-efficient lighting increases, LEDs will become an integral part of horticultural lighting.

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