By Zvi Howard Wener / Chief Agronomist / zviw@zeraim.com

• Total Radiation = visible radiation + invisible radiation.
• Visible radiation is within the 400-700 nanometer wavelength range.

• Radiation necessary for photosynthesis is within the visible radiation spectrum.
• This radiation is called photoactive radiation (PAR) and is measured in microeinsteins/m²/sec.

The above graph of the visible light spectrum compares the human eye's response to visible radiation, as measured in footcandles (lumens/m²), to PAR light, measured by a quantum meter in microeinsteins (microeinsteins/m²/second). As the growers need to know the amount of PAR light available for photosynthesis, quantum meters are used to provide measurements in microeinsteins.

As can be seen in the two graphs below, the light used in photosynthesis is in the blue and orange-red light ranges. The top graph (A) displays the relative absorption spectra of the carotenoids, chlorophyll a and chlorophyll b pigments. The bottom graph (B) shows their relative effectiveness in photosynthesis.

At the Light Saturation Point (LSP) increased exposure to PAR light produces no further photosynthesis, which translates into no further positive impact on crop yield. However, each plant strain has been found to have its own specific LSP.

Zeraim Gedera cultivates varieties of peppers in the Negev and Arava regions in Israel, areas with abundant natural radiation. As a result, the pepper varieties developed by Zeraim Gedera have a higher LSP than other strains and are able to utilize high levels of PAR light, leading to a greater crop yield.