Abstract

Red and blue light are the principal wavelengths responsible for driving photosynthetic activity, yet amber light (595 nm) has the highest quantum efficiency and amber-rich high pressure sodium lamps result in superior or comparable plant performance. On this basis, we investigated how lettuce plant growth and photosynthetic activity were influenced by broad and narrow light spectra in the 590–630 nm range, by creating amber and red light-emitting diode (LED) spectra that are not commercially available. Four different light spectra were outfitted from existing LEDs using shortpass and notch filters: a double peak spectrum (595 and 655 nm; referred to as 595 + 655-nm light) that excluded 630-nm light, 595-nm, 613-nm, and 633-nm light emitting at an irradiance level of 50 W·m−2 (243–267 µmol·m−2·s−1). Shifting LED wavelengths from 595 nm to 633 nm and from 595 nm to 613 nm resulted in a biomass yield decrease of ~50% and ~80%, respectively. When 630-nm light is blocked, lettuce displayed expanded plant structures and the absence of purple pigmentation. This report presents a new and feasible approach to plant photobiology studies, by removing certain wavelengths to assess and investigate wavelength effect on plant growth and photosynthesis. Findings indicate that amber light is superior to red light for promoting photosynthetic activity and plant productivity, and this could set precedence for future work aimed at maximizing plant productivity in controlled environment agriculture.

Highlights

  • light-emitting diode (LED) Spectra in the 590-nm to 630-nm Range Obtained with Optical Filters

  • Shortpass and notch filters incorporated into the experimental LED lighting system resulted in single and double peak LED spectra (Figure 2) that made up the plant light treatments in this study

  • We investigated the influence of wavelength on lettuce plant growth and photosynthetic performance by filtering amber and orange/red light, yielding different spectra with the same irradiance level

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Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Plant lighting experiments show that red (600–700 nm) light plays a critical role in photosynthetic activity and plant development within the photosynthetically active radiation (PAR) spectrum (400–700 nm) [1,2]. Pioneering action spectrum and quantum yield studies using monochromatic light indicate that red light induces higher photosynthetic activity (~20–40%) than other wavelengths in the PAR spectrum for typical greenhouse crops [3,4]. McCree [4] further determined that the highest wavelength peak of the action spectrum was at 620 nm, with a shoulder at 670 nm in the red wavelength range. This study led to the use of red light-emitting diodes (LEDs) in plant lighting systems [2,5]

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