Greenhouse Lighting


If you have an electricity supply installed in your greenhouse, then you can easily add a lighting system to extend the hours you can work and provide a little extra heat for your plants. Whilst standard bulbs may offer enough light to work by comfortably, the addition of special growing lamps will enable you to lengthen daylight hours for the plants. This is useful during the winter and spring when natural light levels are low as it will help to improve the plant's growth.

The light from each portion of the colour spectrum affects plant growth and responses in different ways:

  • Red light: required for flower production, although too much will cause spindly growth.
  • Yellow light: required for chlorophyll production.
  • Blue light: required for photosynthesis; high levels will produce dark green compact growth.

Plants should receive a wide spectrum of light for healthy growth.

When buying lighting, always make sure that the fittings are suitable for the moist, humid atmosphere of a greenhouse.

Growing lamps are available in a number of styles:

  • Fluorescent tubes: available from garden centres or aquarium suppliers. Install approximately 30 cm (1 ft) above plant foliage and fit with a reflector to cast the light downwards. Produces mainly blue light, some green and yellow, but is low in red light.
  • Mercury lamps: should be suspended above the plants for optimum effect. Mercury fluorescent lamps additionally emit red light.
  • Metal halide lamps: produce light that is closer to the spectrum of natural light than fluorescent lighting, with more blue light than mercury lamps.
  • Sodium lamps: produce yellow light through to the red end of the spectrum.

The most balanced light for plant growth may be achieved by using a mixture of mercury, metal halide and sodium lamps. Although these lamps are rather expensive to buy, they produce a high light intensity and are very economical to run.

For healthy plant growth you should provide your plants with an average lighting level of 4,000 Lux, although certain plants may need more. Light meters may be used to accurately measure light levels to ensure that the needs of any plants with specific requirements are met.