In the future, the relatively closed production system of greenhouse will play an important role in meeting the demand for food growth. In recent years, the shortage of greenhouse lighting is more and more get the attention of people, on the one hand is due to greenhouse azimuth, structure, cover material characteristics caused by the greenhouse light transmittance drop, on the other hand is caused by a lack of sunlight greenhouse crops, as a result of climate change, such as a continuous wet weather of winter and early spring season, frequent fog weather, etc. The lack of light has a direct impact on greenhouse crops, causing serious damage to production. These problems can be alleviated or resolved effectively by the plant replenishment lamp.
Incandescent lamps, fluorescent lamps, gold halide lamps, high pressure sodium lamps, and new LED lights have all been used or are being used in greenhouse lighting. In these type of light source, high pressure sodium lamp to occupy a certain market position, but high pressure sodium lamp lighting sustainability, security (mercury) problems such as low, do not close exposure is also very prominent. Some scholars have a positive attitude towards the future or overcoming the low performance of high-pressure sodium lamps. Therefore, this paper summarizes previous research results and its application status, and provides reference for light source selection and application in greenhouse.
The high pressure sodium lamp is the third-generation lighting source, and the conventional alternating current has a wide range of use, high luminous efficiency and strong penetration ability, with a maximum life span of 24000h, and the lowest can be maintained at 12000h. When the sodium lamp is illuminated, it will be accompanied by the production of heat, so the sodium lamp is a kind of thermal light source. In the process of use, there are self-extinguishing problems. LED as the fourth generation of new type of semiconductor light source, the use of dc drive, life can reach over 50,000 h, and attenuation is small, as a cold light source, can be close to the plant irradiation. Compared with the LED and high pressure sodium lamp, it is pointed out that the LED security is high, does not contain harmful elements, and is more environmentally friendly.
Green plants absorb most of the red orange light and wavelength of 400~500nm with wavelength of 600~700nm. The green light with wavelength of 500~600nm is only absorbed by micro. High pressure sodium lamp and the LED can meet the needs of the plant lighting, NASA (National Aeronautics and Space Administration) using LED the first research purpose is in order to improve the energy efficiency, reduce the cost of operation and management, improve the quality of the crops. In addition, LED can be widely used in the production of high-quality medicinal crops, and some scholars have pointed out that LED technology has great potential in improving plant growth.