When looking at lighting in the grow room, growers should look at lighting output and light distribution as this lighting intensity will provide the greatest yields. But, while lighting output and light distribution are important metrics, the light conversion efficiency is also a strong indicator of a successful grow set-up.

There is more than one option to choose from in horticultural lighting technologies. Each technology has its own advantages and disadvantages. The most commonly used lighting systems for supplemental lighting are high intensity discharge (HID), fluorescents, LED grow lights, and sulfur plasma.

High Intensity Discharge (HID)

High intensity discharge (HID) lighting systems include both metal halide (MH) and high pressure sodium (HPS). These systems are still the most commonly used horticultural systems by both growers and indoor horticulturists. They are relatively inexpensive and produce a spectrum of light suitable for maintaining vigorous plant growth.

The biggest advantage of HID lighting systems for supplemental lighting is they can cover a large area without taking up a lot of space. Space is such an important issue because the larger the lighting system, the more it will block the natural sunlight when it is not operating.

Fluorescents

Another commonly used horticultural lighting technology for supplemental lighting is fluorescents. Fluorescent lighting can also cover a large area and is usually a little more energy efficient than HID lighting. The advantages of fluorescents are they are relatively inexpensive and available practically anywhere. Fluorescents run a little cooler because they disperse the heat over the entire length of the bulb (usually four feet in length).

LED Grow Lights

Over the last decade, LEDs have made great strides within the horticultural sector. LED Grow Lights have a few advantages including longevity, being specifically tailored to the light spectrums of plants, and they operate much cooler than HID or fluorescent lighting. LED Grow Lights do not use hoods or ballasts, making them better for smaller areas. Also, LED Grow Lights are used to supplement lost PAR light from cloudy days or greenhouse glass ceilings. Moreover, LED Grow Lights do not require any acclimation time when switching from LED to natural sunlight as their spectrum is so close to mimicking natural sunlight. LED Grow Lights that contain UVA light are able to fuel certain carotenoids that HID do not as HPS fixtures do not contain UV light.

Due to their cool operation, LED Grow Lights are more energy-efficient than other horticultural lighting technologies. This works well for gardeners in warm climates who are looking to extend the growing season. However, growers who require additional heat may want to choose HID lighting over LEDs. The largest disadvantage of LED Grow Lights is the initial cost. However, due to their longevity and lower energy costs, LED Grow Lights can be viewed as a long term investment.

Sulfur Plasma

Sulfur plasma light systems are relatively new to the horticultural sector. These lights produce a spectrum closer to that of the sun than any other artificial lighting technology. Because of this, they make excellent supplementary lighting systems. Although plants do well under any type of supplementary lighting system, they can adjust most easily to sulfur plasma because of its unique spectral output. In other words, there is less acclimation for the plant when switching from sulfur plasma to natural sunlight than with other artificial light technologies. Like LEDs, sulfur plasma lighting lasts close to ten years. Sulfur plasma fixtures run cooler than HIDs but not as cool as LED Lights. The biggest disadvantage of sulfur plasma is the initial cost of the system.