Effects of plasma vs. high pressure sodium lamps on plant growth, fruit yield and quality in greenhouse cucumber production

High pressure sodium (HPS) lamps have traditionally been the main light source
for supplemental lighting in greenhouse crop production because of their high reliability
and efficiency in producing photosynthetically active radiation (PAR) - the light useful for plant photosynthesis and growth. The light spectrum of HPS has much less proportion of blue light in comparison to sunlight. Therefore, plant growth and development could be benefited from an alternative light source with a spectrum similar to sunlight and containing more blue light, such as the recently developed plasma lamps. Some growth chamber studies reveal that plant growth and development was indeed better under plasma light in comparison to HPS, when
plasma light was used as the sole overhead light source. Plant responses to plasma in
greenhouse conditions could be different because the plant is also exposed to natural
solar radiation. Therefore, this study investigated the impacts of plasma light on
greenhouse-grown mini cucumber (Cucumis sativus L. ‘Picowell’) growth, fruit yield
and quality, in comparison to HPS light over two winter seasons (October 2012 to
March 2013 and October 2014 to April 2015) in a 200-m2 greenhouse. The
greenhouse was divided into 4 sections (50 m2 in each section); two sections were
fitted with plasma light while the other two sections had HPS (2 replications). Both
lighting types provided the same amount of PAR (165 μmol m-2 s-1). For both seasons,
the total fruit yield was not affected by the lamp types. However, in the first season
(October 2012 to March 2013), the cumulative marketable fruit yield under plasma
was significantly greater than that under HPS light. Due to the different impacts of
the light types on marketable fruit yield during the two winter season, future research
should focus on the proper light source for supplement sunlight in year-round greenhouse vegetable production.