Quantitative methods for evaluating the conversion performance of spectrum conversion films and testing plant responses under simulated solar conditions

Spectrum conversion film (SCF) is a covering material that modifies incident solar spectrum to more-active wavelengths in photosynthesis. Due to its fluorescence property, the performance of SCF cannot be accurately evaluated in a conventional way for agricultural films. We proposed quantitative methods to evaluate the conversion performance of SCF and tested the plant responses. The performance of GR films [green light (500–600 nm) to red light (600–700 nm)] containing different concentrations of dye (40–3000 ppm) was tested in comparison to a transparent film (control). A method for estimating light emission was developed using a series of equations and values measured under artificial lighting. The spectral properties and photosynthetic rates of sweet pepper (Capsicum annuum L.) leaves covered with the GR film were measured using a solar simulator. The emission of GR film was detected using a spectroradiometer connected to an integrating sphere instead of using a spectrophotometer used in the conventional method. The transmittance of GR film and its change rate of transmitted photon flux densities at emission wavelength differed depending on the light source. The change rate calculated through the equations was constant within the target spectrum and could be used as a basis for conversion performance. The solar spectrum modified by the GR film caused to increase the red light reaching the leaves by 10.47% and thereby increased the photosynthetic rates by 15.41% compared to the control. The photosynthetic efficiency based on incident and absorbed photons under the GR film increased by 22.14% and 21.87%, respectively. These methods were proposed for quantifying spectral properties of SCF under the solar spectrum, confirming the application of solar simulator for photosynthetic evaluation. When used as a standard light source for SCF, a solar simulator provides indoor test conditions with a spectrum similar to solar radiation without long-term cultivation or a large-scale film test.