Digitally Fabricated Mobile Spectrometer for Multipoint Continuous Spectroscopic Analysis of Light Environment in Greenhouse Tomato Canopies

A low-cost spectrometer, featuring a micro electro mechanical systems (MEMS) sensor, was designed and manufactured using digital fabrication techniques. The spectrometer was morphed into a zelkova leaf-shaped case using a three-dimensional printer. The control software, written in the Arduino sketch programing language, measured the flux of photons in the 400―800 nm range, at 1 nm resolution, every 5 min. The obtained data were saved on a micro SD memory card in the comma separated values format. The spectrometer continuously operated for more than 3 d using a type B universal serial bus micro connector and a 10 Ah mobile battery. Four manufactured spectrometers were installed inside and outside of a tomato canopy in the experimental greenhouse of Wakayama prefecture, and continuously measured the spectroscopic flux of photons for nine d. The quantitative changes in the phytochrome photoequilibrium in the tomato leaves were estimated using the data from the continuous spectroscopic analysis. The effect of pruning under leaves on the illumination in the tomato canopy was quantified in terms of the leaf area index. We expect that the proposed low-cost and high-mobility spectrometer will be used in plant production fields.