Problems of standardising illumination for plants in greenhouses and green structures

Today greenhouses are transformed. In the middle of the past century, they were almost glazing buildings above the ground. Due to the development of planting technologies, including mats or trays with substratum, aero – and hydroponics, etc., greenhouses now can be anywhere, including underground. This gives impetus for urban agriculture with optimal logistics (growing near consuming). Indoor green structures become more and more popular. The illumination of them is very important because plants lose decorative properties in unfavourite conditions. At the beginning of this century, there was an analysis of a lot of failed attempts to create winter gardens on underground floors. The illumination was calculated successfully by today’s norms, but the plants withered. This is because the norms were developed for natural-illumination greenhouses. Usually, the illumination is measured in lux or μmol/day. The first unit is weighted by wavelength according to the people’s eyes sensitivity. The second one accumulates all photons. But the plants have another photosynthetic activity curve. They use two photosynthetic substances – chlorophyll and beta-carotenoid (active on the green light). The chlorophyll changes its absorption curves dependent on solvent presence (a and b). This allows some variability for adapting to the light spectrum, which is used by water plants. Thus, both units do not apply to artificial illumination. In this work, we analyse the curves of solar and phytolamp spectrums, averaged sensibility and spectral luminous efficiency for photopic vision. Integration of the curves allows recalculation of the lux-meter reading to the equivalent solar illumination or the last one to the phytolamp power. We propose a new unit system – phytocandela-phytolumen-phytolux – according to the photosynthesis efficiency curve that is numerically equal to candela-lumen-lux under sunlight. This shows that lux may not be a base unit because it is related to a single biological species but not a physical property.