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'Applied Sciences' selects NCNU research paper as February cover story

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Water bamboo (Zizania latifolia) is considered a delicacy in Taiwan. Almost 90% of the nation’s annual yield of water bamboo is cultivated in Puli Township, Nantou — the proverbial heart of Taiwan and home of National Chi Nan University.

A multi-departmental NCNU team designed a light-emitting-diode (LED) lighting system for a water bamboo field during winter season at night, and the results indicated that this lighting system can prevent the stunting of water bamboo leaves and further assist their growth. Compared with previous LED systems, in which the LED bulbs were placed directly above water bamboo leaves, this LED lighting system presents the added benefit of easy handling during harvest. To prevent the inhomogeneous coverage of LED light patterns, a new kind of LED lenses was also incorporated.

This research experiment has its roots in 1999, when Taiwan’s water bamboo farms were attacked by basal stalk rot, leading to leaf stunting. Dr. Jin-Hsing Huang investigated the causes of this disease. Finally, he cured stunting without using chemicals after noticing how water bamboo that grew near a ridge did not stunt. By observing environmental variables, he reported that street lights built near the ridge provided light during the night, which further helped leaves grow and prevented stunting.

He taught farmers to use lighting equipment for increasing the yield of water bamboo from one to three harvests per year. Supplying light to water bamboo at night during the winter season — defined as between September and December — when natural sunlight is not sufficient for the growth of young water bamboo leaves yielded admirable harvests. Taiwanese farmers began using a high-pressure sodium (HPS) lamp as the source of light, an electricity-intensive and less-durable alternative to LEDs.

Moreover, according to the farmers, the use of HPS lamps to prevent stunting disease can indirectly damage the habitat of frogs and possibly other species present near the field because of its strong and shining glare. The possible adverse effect of LEDs on the environment is under investigation. 

For this scientific study, the NCNU team comprising members from the departments of applied materials and optoelectronic engineering, electrical engineering, liberal education, civil engineering, and information management purchased LED modules from an original equipment manufacturer (OEM) company, which fabricated an LED lamp with different lenses and power setup according to pre-specified designs and requirements.

To evaluate the relationship between light intensity and growth of bamboo leaves, the NCNU team measured the height of water bamboo leaves for two weeks during the night. The exposure time during the night was approximately 10 hours. Several observation spots near the ridge exhibited a slow growth rate. The coverage measurement of LEDs was completed using a spectrometer and the unit of lux, in which different colors indicate different light intensity. After two weeks, the corner area exhibited the weakest light intensity, with the lux decreasing with each increase in distance.

Studies have reported that blue and red lights emanate the most important wavelengths for the growth of plants, therefore the use of the correct equipment to measure the LED light intensity is essential for determining the sufficient amount of artificial light, especially of the LED variety, for plant growth. In the designated field, 80% of water bamboo plants received sufficient LED light exposure.

To solve the problem of the inhomogeneous coverage of LED light, the NCNU team performed indoor measurements of light intensity dependent on the distance and obtained a suitable arrangement of LED light modules by incorporating a 60×60 LED light distribution pattern. These findings can not only be used as a reference for water bamboo farms, where a light supply is required at night during winter, but can also be applied to other crops such as dragon fruit and sugar apple.

Featuring an ethereal nighttime photo of water bamboo plants bathed in soft purple light, “Optimized LED-Integrated Agricultural Facilities for Adjusting the Growth of Water Bamboo (Zizania latifolia)” was published by SCI Journal “Applied Sciences” as the cover story of its February issue.

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