Lighting in Horticulture

This issue has a strong focus on lighting in horticulture, including the latest research and development in light-emitting diodes (LEDs). Representing the biggest advancement in horticultural lighting since the development of High Intensity Discharge (HID) lamps, LEDs are increasingly used for controlled environment research (growth chambers), lighting for tissue culture, lighting for plant propagation (plant factories), and supplemental and photoperiod lighting for greenhouses in countries with seasonal low light levels.

Compared to HID lamps, LEDs have the ability to control the spectral composition, the ability to produce very high light levels with low radiant heat output when cooled properly, and they maintain useful light output for years without replacement. Significantly, LED is the first light source with the potential to match wavelengths to plant photoreceptors to optimise plant growth and yields, and to influence morphology and composiiton. In today’s digital age, LEDs can be integrated into control systems to deliver lighting programs such as ‘daily light integral’ lighting, and sunrise and sunset simulations. Other advantages of LEDs include their light weight compared to HID systems, safer operation than current lamps because they do not have glass envelopes or high touch temperatures, and they do not contain heavy metals such as mercury.

Despite these advantages, many commercial growers are reluctant to embrace LED lighting, mainly because of cost, and also because of little research for specific crops. Since its first development by NASA in the late 1980s and early 1990s, to provide red and blue light for plant growth systems designed for research on the space shuttle and space station, the technology has progressed to high-density, multicolour LED chip-on-board devices. With more light output and decreases in device costs, LEDs are becoming more economically viable for large-scale horticultural applications. However, there is still much more work needed before LEDs truly become an efficient and economical lighting source. Not least is research to better understand the role of colours in plant growth, not just red and blue;  the ‘genome’ of plant lighting for want of a description. Only then will LED lighting fulfil its promise. In this issue, we learn a little more about LED lighting developments, as well as advances in  light-emitting plasma lights (LEPs).

Light is also the focus in our two articles testing Harmony shade screens in greenhouse tomato facilities. The first describes a major study comparing Harmony shade screens to a greenhouse that has been whitewashed. The joint study was carried out by screen secialist Svensson  and Spain’s Andalusian Institute for Research and Training for Agriculture (IFAPA). The Harmony mobile screen system enabled the tomatoes to receive 31.2% more light than the whitewashed greenhouse during the course of the experiment, with a significant increase in fruit production. This study is supported by Grodan trials on a greenhouse tomato crop  to maximise production and quality with a reduced environmental footprint, using the XLS 20F Harmony Revolux screen. Both these articles have relevance  for commercial greenhouse operators located in hot, dry regions, not only in the southeastern Spanish province of Almería and the Mediterranean Basin, but also in the hot, dry regions of Australia.  Enjoy the read!

Steven Carruthers