Besides the common lightning you can also use growing lamps. The special quality of lighting produced by growing lamps is required to increase light intensity and daylength for specific purpose during spring and winter when light levels are low. Fluorescent tubes that produce the light needed to improve the plants growth may be bought from specialist aquarium suppliers and garden centers. Theses do not produce much heat and may be placed close to the plants.
For best results they are fitted with reflectors that cast the light down-wards, where is most needed. For greatest effectiveness the tubes should be mounted 25-30 cm above foliage. Most growing lamps that are suitable for use in the greenhouse need special fittings because of the moist and humid atmosphere. If you have any doubt you should ask the advice of an electrician.
You may also want to use some light meters where lighting is a very important factor for your plants. Special plant light meters may be useful in the greenhouse because they measure the light levels much more accurately than can be judged by eye. Light meters are usually supplied with information about the light levels that are preferred by a wide range of commonly cultivated plants.