LIGHT MEASUREMENTS AND PLANT GROWTH

An investigation has been carried out to assess the reliability of different sensors for measuring light reaching plants grown in one type of plant growth room fitted with fluorescent tubes. Particular emphasis has been placed upon: (1) the comparison between selenium and silicon detectors (2) the influence of detector size and (3) the type of cover placed over the light sensing material. Regressions of plant dry weight against the amount of light indicated that seedling tomatoes and lettuces were related more consistently to measurements made by silicon rather than selenium detectors. Correlation coefficients (r) between plant dry weight and light measurements were generally higher if a cover of semi opaque perspex was placed over the detector. The thickness of the cover, the detector size and the position of the detector in relation to the cover also affected the r values.