LED lighting is a newer technology for horticultural lighting that generates light by passing electricity through semiconductor materials. It replaces traditional HID lighting that works by superheating bulbs filled with gas.
An LED light is made from light emitting diodes powered by a DC power supply. Some LED lights also have a heatsink, a fan, and sometimes a protective casing.
LED lights are available in different shapes, rectangles, squares, long strip lights, or mounted in tubes.
A worthwhile feature available on some LED lights is a dimmer switch. Plants in early stages of growth need less light than plants in late flowering. A dimmer switch allows the light intensity of a panel to be turned down so it can use less power during the plants early growth stages and then turned up for later stages when plants require more light. This feature can save on electricity costs and reduce heat. It also allows for gradual light increases. Plants prefer gradual increases to intensity, not abrupt change to a higher light level.
Most LED lights are directional, meaning they emit light at 180 degrees, directly down at the plants. Directional light is efficient, saving costs compared to other types of lighting. For example, HID lights emit light over 360 degrees, requiring reflectors to bounce light back at plants. Light that needs to be reflected back is less efficient because whenever light gets reflected some energy is absorbed by the reflector. A straight path to the plant canopy is better.
The chart below shows the light distribution for a 20 x 26” light panel. The numbers indicate light readings taken under the light. It demonstrates how light becomes less intense the further away from the centre point directly under the light fixture.
Reflectors positioned at the sides of the canopy, such as the silver reflective walls of a 4’ square grow tent, will reflect some light, boosting light levels at the sides.
Light panels positioned beside each other can be arranged so that the beams overlap, creating a spread of even intensity over a large coverage area. This is called a grid pattern.
LEDs create light by electroluminescence, which is the phenomenon of a semi conductor material emitting light when an electric field is passed through it. The type of semi conductor material used in LEDs determines the colours of light it emits. For example, indium gallium nitride is a material used for blue and green LEDs, and aluminum gallium arsenide is used for red LEDs. Different semiconductor materials can produce specific wavelengths of light. LED panels that house a mix of different LEDs can output customized light recipes by combining wavelengths.
LED panels are very efficient because they are designed to produce only the wavelengths of light that plants use. In comparison, HID light systems emit a byproduct of infrared light which is not useful for plants and also adds a lot of heat to a grow room.
LED systems also generate heat, but not from a bulb with superheated gasses, as is the case with HID lights. The heat created by LEDs is created by its semiconductor processes.
LED systems generate less heat overall than HID systems. HID systems turn 20% – 40% of power into usable light. LED systems convert about 40% – 60% of power into usable light.
Heat generated by LED semiconductors is removed using passive and active cooling methods. For passive cooling, heat is conducted away from the semiconductors, either through the board the LEDs are mounted on, or a finned heatsink. For active cooling, fans blow heat off the board and heatsink.
Because heat is dissipated away using active and passive cooling methods the front of an LED panel is cool to the touch. Plants can be positioned very close to a light without a risk of starting a fire. Having plants positioned close to the light also saves energy. The further light has to travel from the panel to reach the plants the less intense it gets. The further away the plants are from the light source, the more power a fixture has to draw to generate enough strong light for the plants. Lights don’t have to work as hard when plants are closer to them.
A good LED light panel should last a very long time if properly cared for. Although it varies from light to light, an LED grow light lasts on average 60,000 hours. In comparison, HID light systems last only 20,000 hours.
The output of an LED light will degrade over its lifespan. Over 60,000 hours, a loss of 3-5% can be expected.
LED light boards and heatsinks are solid state. There are no moving parts that can become detached or gasses to leak so they aren’t prone to breaking down over time.
Excessive ambient heat will shorten the lifespan of LED lights and degrade their performance. To prevent heat damage, the ambient temperature in the grow room should stay under 30°C.
To prevent damage from static electricity, anti static gloves should be worn when handling LED boards. Devices and equipment in the production area should be well grounded.
Some LED boards are housed in a protective casing. The casing is sometimes rated for water and dust resistance with the Ingress-Protection code, or IP. It is expressed as IP with two numbers afterwards. For example, IP64. The first digit indicates dust resistance and the 2nd digit indicates water resistance. The symbol X in place of either the 1st or 2nd number indicates that there is no data available.
Dust resistance rating (1st digit):
less than 5 = poor dust resistance
5 = some dust resistance.
6 = completely protected from dust.
Water resistance rating (2nd digit):
less than 3 = resistant to some drips, but vulnerable to sprays.
3 = resistant to damage from spraying water.
6 = resistant to powerful jets of water projected at enclosure.
LED lights can be run without a protective casing as long as they aren’t sprayed directly with water and are cleaned periodically using isopropyl alcohol to remove dust.