LED Light Sources and Their Complex Set-Up for Visually and Biologically Effective Illumination for Ornamental Indoor Plants

Ornamental plants are often used in indoor environments as part of biophilic design to improve the health and wellbeing of occupants, and to support sustainable, green architecture. Unfortunately, many plants do not thrive and need to be continuously replaced, which is economically unsustainable. The wavelengths and spectrum ratio of commonly used light sources such as light emitting diode (LED), and the lack of an appropriate light dark cycle (photoperiod), appear to be crucial influencing factors. Therefore, this study focuses on determining the optimal action spectrum of LEDs for visually and biologically effective illumination for plants, and humans as end users. This practice-based research study applies critical analysis of literature, photographic evaluation of the appearance of plants under various LED lighting in the form of a visual assessment questionnaire-based survey, and provides various measurements that record the properties of light including correlated color temperature (CCT), color rendering index (CRI), spectral power distribution (SPD), peak light wavelength (λP), photosynthetic photon flux density (PPFD) and daily light integrals (DLI). Research confirms the LED lighting used for horticultural food production cannot be applied to ornamental indoor plants due to fundamental differences in purpose. Such illumination provides fast growth for market consumption and usually makes plants appear unnatural, whereas ornamental plants in an indoor environment should grow at an appropriate speed which reduces maintenance costs and they should have a natural appearance. These new findings, supported by evidence and data, can help investors, clients, architects, landscape and lighting designers, as well as luminaire manufacturers, make improved, biophilic-sustainable lighting design choices