Lighting

Commercial horticultural lighting falls into two types: replacement lighting and supplementary lighting. Replacement lighting generally ‘replaces’ natural sun light with artificial sources of light and is normally used in a growroom or research facility where total control is necessary. However, for the purpose of this, the focus will be on supplementary lighting; where you ‘top up’ natural light from artificial sources. This is by far the most common use of these products in commercial horticultural situations.

Benefits of commercial horticultural lighting (dependent on conditions):

  • Year round production (out of season crops)
  • Increased plant growth and yields
  • Optimal growth conditions
  • Better quality products
  • More control by being able to extend light periods

Due to poor winter daylight in the northern hemisphere being the limiting factor for plant production from November to March, the use of commercial horticultural lighting is fast becoming an integral part of commercial growing – controlling both the quality and the quantity of produce grown. The development of lighting has become an important factor in order to grow plants of a consistent quality and to harvest at the correct time to achieve maximum price.

There are two important factors that commercial horticultural lighting must satisfy – that the source is highly efficient in terms of the light produced is high in proportion to the energy consumed by the lamp and, the light must have the correct spectral output.

Plants need lighting with a wavelength of between 440nm and 700nm (nanometres) called the PAR area, which stands for Photosynthetic Active Radiation. The number of photons (light particles) reaching the plant in a given time frame is one of the factors that determines the rate of photosynthesis.

It is generally understood that light in the blue-green end of the PAR spectrum enhances seedling/cutting and vegetative growth. It tends to make for stronger, hardy plants with shorter internode spacing. Light at the orange/red end of the spectrum tends to trigger flowering and encourages softer more rapid growth. When propagating or for producing foliage only plants, metal halides are often the preferred choice. For flowering or fruiting stages and for photo-period manipulation, high pressure sodium lamps are the preferred option.

Overall, high pressure sodium lamps are the most widely used for horticultural purposes because they have an acceptable spectral distribution, long lamp life and the highest radiant efficiency, which makes for low running costs; this is especially true of the 600w size range.

More and more commercial growers are using supplementary or assimilation lighting to assist their business whether growing hydroponically or not. The use of these lights will give you healthier, vigorous plants. In summary, commercial horticultural lighting can be useful in a number of different situations, for different crops for different reasons at different times of the year.

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    Iain Reynolds

    Iain Reynolds