A historical overview of LED lighting use in horticulture.

Testing of LEDs for plant growth began in the United States with the development of the first crude LED arrays at the end of the 1980s and beginning of 1990s. The blue LED technology was not sufficiently advanced to provide useful levels of blue irradiance, therefore studies were conducted using red (660 nm) LEDs alone or in combination with blue fluorescent lamps. First attempts were done because of the need to develop better lighting sources for space plant growth systems. At the beginning of 1990s LEDs began to be tested for germinating seeds and rooting cuttings in the Netherlands and for tissue culture systems in Japan.

In the beginning, the cost of LED lighting systems was very high, therefore LEDs usage to crop growth has been restricted primarily to research in controlled environments. The work, in the beginning, was mostly related to plant production under LEDs. This work was needed for preparation for the development of plant-based regenerative life-support systems for future Moon and Mars bases.

The first experiments with red LED arrays were made of individually lensed devices. Then only the red devices (660 nm) had light output adequate for plant growth. It was not suggested for large-scale use because of cost, uneven performance of individual devices, and fabrication difficulties.

Lighting panels were restricted to less than 1 m2 in area. At the same time, the Japanese have built larger arrays for plant growth. Following by new LED chip technologies became available and LED modules using very high-density chip-on-board technology were developed. This technology was too expensive for large-scale use. It was ideal for research applications that require high light output at several independently controllable spectral bands.

At the end of 1999s and at the beginning of 2000s high-output LEDs led to automated manufacturing, the fabrication of LEDs arrays greater than several square meters in the area has become more economically feasible.

Horticultural lighting utilizing light emitting diodes (LEDs) was introduced to the general public in the first few years of the 21st century. Since then, improvements in technology and pricing have made LED lights a viable alternative to the traditional and very effective High-Intensity Discharge (HID) systems while using only about 35% of the electricity required by HID lights.

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