A low cost sunlight analyser and data logger measuring radiation

Abstract

Growing conditions in the early stages of crop development can be critical to eventual yield. This is true for a wide variety of crops such as lettuce, maize and rice. These conditions include not only soil quality, moisture and temperature, but also the quality and duration of available sunlight. A simple measure of ‘brightness’ is however not a good indication of the true ‘quality’ of the sunlight available. Research has shown that the presence or absence of specific wavelengths of light (particularly infra-red (IR), red and blue) can significantly affect photosynthesis and hence crop growth. Further, over exposure of plant tissue to high levels of ultra violet radiation can prove damaging. IR radiation is known to be scattered by weak levels of cloud and haze, and is significantly absorbed by moderate cloud conditions, resulting in lower levels reaching the ground. Ultra violet radiation is capable of penetrating even moderate levels of cloud. The total amount of quality sunlight received by an immature plant can affect its later yield, determining whether a crop is worth harvesting, or influence the later use of fertilizers or the real time control of supplementary, wavelength specific illumination. This paper discusses results from a low cost, real time, stand-alone LED based sunlight analyser and data logger capable of making both quantitative and qualitative measures of specific wavelength bands, and distinguishing sunlight conditions ranging from direct sun, through light haze, moderate cloud and even moonlight. The unit costs less than 10 Euros and can give in excess of 4months unattended monitoring and logging using 3 alkaline AA batteries, storing to an internal 32Mbit Flash EEPROM and transmitting via a 2.4GHz RF link.