Ugrow Organic: Lighting

Artificial indoor lighting for the grower has concentrated on two main stages of plant growth; the vegetative & flowering stage.

During the vegetative stage the plant is develops leaves and general form whilst during the flowering stage the plant prepares for reproduction. Traditionally lighting for these two stages has led to two different light bulbs being used.

The blue and white light of a metal halide (HID) light is frequently used for plants in their general growth stage and sodium lamps (HID), which emit a red light are used during a plant's reproductive stage.

More recently a new form of sodium light (universal lamps) have emerged which many view as an adequate replacement for the two light types.

However, there are other factors to consider when choosing the type of lighting unit and bulb to use. For example, fluorescent lights can be of use to the grower particulary during the very early stage os growth. Also, light enhancers such as reflectors and light movers are available which aid in the amount of light (lumens) a plant receives.

Fluorescent lights

The growers choice before the introduction of high intensity discharge (HID) lighting, fluorescents are ideal for small scale indoor hydroponic systems used to grow small plants such as herbs. They are also suitable for propagation of seeds and cuttings. Although feasible, fluorescent lights are not suited for growing larger plants as their lower depth of field compared to HID means the plant has to be kept very close to the fluorescent tube. Many tubes would also be required to provide an adequate spread of light for larger plants.

Fluorescent tubes also loose some luminosity throughout their life span and need to be replaced on a regular basis. However, on a small scale system fluorescent lights are a viable option: the tubes are inexpensive and the lighting unit usually comes complete with ballast and fittings which are of low cost.

There are a number of different types of tubes available specifically for growing plants, examples being vita-Lite* and Ultralume 5000. Tubes which loose little luminosity throughout their life span are also available.

High Intensity Discharge (HID)

The introduction of HID made a significant advancement to hydroponics. HID lights burn more intensely and evenly compared to fluorescents. HID soon became the grower's choice. HID lighting requires a ballast to ensure the electrical current powering the light is stable. However, ballasts can be heavy and cumbersome. As a consequence there are HID lights with ballasts integrated to make a HID lighting unit or available remotely away from the bulb. Some growers prefer a remote fitting because the ballast can be supported away from the light on a floor or shelf whilst only the bulb and reflector unit is suspended from the ceiling.

Metal Halide

Until the relatively recent introduction of 'universal' sodium lights metal halides were viewed as the standard lighting in many hydroponic systems. Metal halide provides a spectrum as close as possible to that of natural sunlight and coupled with their intensity and energy efficiency, make them ideal for indoor gardening. However, they are not suited to lighting plants which are at the flowering stage due to inadequate red/orange light levels.

High Pressure Sodium lights

These emit a narrower spectrum of light compared to metal halide but the red spectrum which they emit is of benefit to plants at the flowering stage. Due to a limited spectral output they are particularly effective when used along side metal halide in a hydroponic system.

However 'next generation' sodium lights, with enhanced levels of blue to white light are now available which give a much broader spectral output which many growers use without a need for a metal halide light. Sodium lights also last longer and burn brighter than metal halide and are more energy efficient. These sodium lights are constantly being developed and seem the light of the future for hydroponics.

Light Reflectors

The term, 'you get what you pay for' is particularly apt when discussing light reflectors. Whilst cheaper alternatives are available on the market, the better quality products, developed through years of research can reflect up to 30% more light than their cheaper counterparts.

Light Movers

Light movers move the light above the plants slowly throughout the course of a light cycle. This gives uniform growth and saves maintenance time in a system as the grower does not need to rotate their plants to ensure each plant receives the same degree of light. Such devices include the 'Lightrail 3' which are suited to rectangular growing areas and prevent shading.

Power Consumption Electricity costs incurred through the use of a hydroponic system should not discourage growers from selecting proper lighting equipment. Electricity costs are quite low even when using HID lighting and the rewards gained by excellent plant growth are worthwhile. A 400 watt metal halide light on a 12 hour a day time cycle will cost just 38p a day (where one unit of electricity is 8p) or £11 to £12 a month.