Abstract
The spectral transmission properties of various clear plastic films which were produced for crop protection were examined over the wavelengths from ultraviolet to infrared.
In the plastic films used, the transmission varied drastically in the ultraviolet and infrared regions but not much in the visible one (Figs. 1 and 2.) . Some films were almost opaque in the wavelengths shorter than 350 nm. The transparency in the near ultraviolet region had no direct relation to the film materials such as polyvinyl chloride (PVC), polyethylene (PE) and ethylenevinyl acetate copolymer (EVA) (Fig. 1) .
The infrared transmission, especially in the range of 7-15μ, varied widely with the material of films, i. e. PE films were highly transparent but PVC films were almost opaque, while EVA films were in the middle of PE and PVC films (Figs. 2-6) . There was no substantial difference in the infrared transmission properties among the films of the same material, regardless of the kind of brands (Figs. 2 and 3) .
The transmission in the ultraviolet and visible regions of PVC and PE films was decreased remarkably by the practical use, but it was recovered partially by cleansing them. The infrared transmission was, however, almost no change even if the film was soiled or cleaned (Figs. 5 and 6) .
