Light-cascade technology applied to agriculture

Light cascade greenhouse cover
Greenhouse equipped by Cascade Light Technologies.

The interest in the use of light-cascade greenhouses stems from the desire to increase harvested mass without altering quality or modifying the growing period. The principle of light cascade applied to plant photosynthesis gives a 20% to 80% increase in yield mass. Applied to greenhouse covers, the main effect of the light cascade technology is to shift the solar spectrum into the wavelength range most efficient for photosynthesis.

In addition to fertile ground, water, and sufficient CO2, plant physiology requires one other very important input—light—which must be available in the correct amount and at the correct wavelength. The action spectrum for the majority of green plants peaks between 400 to 510 nm and 590 to 750 nm (see figure below), which correspond to the absorption of the chromoproteins cryptochrome and phytochrome, respectively. The products of the light-dependent reactions are ATP from photophosphorylation and NADPH from photoreduction. These products provide the energy that drives the light-independent reactions which convert CO2 and other compounds into glucose.

Shifting the solar spectrum to optimize photosynthesis

Plant physiology does not exploit the green and UV portions of the solar spectrum for photosynthesis. To exploit these portions of the spectrum, the light cascade principle can be applied to greenhouse covers to shift the energy in these parts of the spectrum into the portion of the spectrum that is most efficient for photosynthesis, as shown in the lower image at right.

The LPRL has doped greenhouse-cover materials such as PEBD/EVA by optically active molecules (OAM) that redshift the incoming radiation. The majority of the optically active molecules used are organic molecules due to their solubility in organic host matrices such as PEBD, PMMA, Polycarbonates, Polyethylene, Acrylic, etc.

The benefits of applying light cascade materials to greenhouse covers are

1. to absorb UV radiation between 360 to 400 nm and to re-emit the energy in the blue band from 400 to 490 nm. This energy is added to the natural solar energy already present in this band.

2. to absorb radiation in the band from 510 to 580 nm and re-emit in the red band from 650 to 720 nm. This energy is added to the natural solar energy already present in this band.

3. to assure an optimum diffusion of solar radiation to limit the effects of shading that reduce the photosynthetic efficiency towards the beginning and the end of the diurnal period.

4. to improve the thermal characteristics of the greenhouse by limiting the loss of thermal radiation from the soil (especially important in winter) and, conversely, to reduce the diurnal temperature during the summer period by limiting influence of solar IR radiation.

Absorption bands for photosynthesis
Shift of solar spectrum for photosynthesis

Field tests

The first field tests were done at the Plant Physiology Laboratory of the CNRS (Laboratoire de Physiologie Végétale) on tomato plants. The results, compared to control plants grown in a nontreated greenhouse, are given below:

1. Leaf mass : 73% increase with respect to nontreated greenhouse cover;
2. Leaf surface : 36% increase with respect to nontreated greenhouse cover.

Tests carried out at the Institute ENTIH at Angers on green-bean varieties also showed an increase in the harvested mass. The result for the CRISTAL variety is shown at right. After
less than two weeks, an increase in yield of almost 100% is achieved. Other plants tested are listed in the table below. Overall, field tests show an increase in yield mass per unit area of 20% to 80%.

Table showing plants tested
Strawberry greenhouse covers treated by Cascade Light Technologies
Strawberry greenhouses covers treated by Cascade Light Technologies.

Light cascade to optimize growth of microalgae

Microalgae (chlorella) were grown in transparent tubes optimized by the LPRL light cascade technology (see tubes at right). The result after 4 days of growth is a 50% increase in the mass of dry matter with respect microalgae grown in clear tubes, as shown in the graph below.

LPRL, 18-20 rue des Presles, 75015 Paris, FRANCE