A study of the transmission of light through a greenhouse roof covered with flowing water is presented. The transmission was estimated for a horizontal pane of double strength glass with and without a layer of water, using basic optical physics. The light transmission through still water on a horizontal pane of glass and flowing water over an inclined pane of glass was measured in both the photosynthetically active radiation (PAR) range (0. 4 to 0. 7 mu m) and the full solar shortwave (0. 3 to 3. 0 mu m) range. Results indicate that the presence of a smooth film of water increases the PAR transmission but greatly decreases the transmission of wavelengths longer than about 0. 8 mu m. The individual ripples produced from the flowing water greatly affect the magnitude of the light transmission, but they are short enough in duration and widely spaced enough that the overall transmission is similar to that of a smooth film of water when the sun angle is within 60 deg of perpendicular to the surface. For incidence angles greater than 75 deg, the flowing water decreased PAR transmission. The difference in total yearly and winter-time transmission between a greenhouse with and without water is compared. Estimates are made using different latitudes and greenhouse azimuth angles. Water increases the PAR transmission by no more than 2% for any latitude, azimuth, or time of year.
|Number of pages
|Transactions of the American Society of Agricultural Engineers
|Published - Jan 1 1987
All Science Journal Classification (ASJC) codes
- Agricultural and Biological Sciences (miscellaneous)