Re-interpreting the photosynthetically action radiation (PAR) curve in plants

The basis of a plant's spectral response of photosynthesis, or the photosynthetically active radiation (PAR) curve, is derived from earlier studies nearly five decades ago. These studies reported that blue and red light were the primary wavelengths; however, shifting within red and blue peaks (10-40 nm) in addition to different PAR curve shapes was observed. In recent years, the McCree curve, which is considered the standard for spectral response of photosynthesis, has been challenged because of experimental design and differences between photosynthetic and whole-plant growth responses. Therefore, this overview provides an amalgamation of all the PAR curve studies, with a focus on narrow spectrum light characteristics, including light measurement units, full width at half maximums (FWHMs) of narrow light spectra, and light intensity levels. While replicating these pioneering works with higher wavelength resolution and narrower light spectrum across the whole visible spectrum is still challenging, we hope that this re-interpretation of PAR curves in plants can elucidate and provide in-depth insight into spectral responses of photosynthesis. We leave the readers with some different perspectives and prospects that need to be considered for future studies.