Plants need light for photosynthesis. The light is absorbed by chlorophyll in the leaves and converted into chemical energy. Plants especially use the orange and red range of the spectrum as well as blue light.
For a green wall project, and if the light spectrum is known, the daily amount of light can be calculated from the illuminance on the green wall and the duration of lighting. However, the illuminance must be converted into the “photon flux density in the photosynthetically active radiation spectrum”, or PPFD (photosynthetic photon flux density). These specify a PPFD value for an illuminance of 1000lx as a function of the spectrum used. Below is a chart of the PPFD values of ERCO’s High power LEDs.
As a reference value for illuminating green walls with tropical plants, a DLI of 1.5 – 4 is recommended (Torres and Lopez 2008; Tazawa 1999). DLI stands for the “daily light integral”., and describes the quantity of photons that a plant receives during one day. A DLI of 2 with the appropriate LEDs corresponds to an illuminance of around 2500lx over twelve hours on the leaf surface.
Photo: Monolithic Power Systems | Botanical Designs, Kirkland, Washington. Copyright Botanical Designs.