The Owner Built Home & Homestead
(Page 4 of 7)
July/August 1972
By Ken Kern
The obvious solution here is to use a type of translucent material which admits the maximum amount of light, and maximum quantity of ultraviolet radiation and the minimum degree of infrared intensification. Fiberglass plastics meet these specifications: as much as 95% of the ultraviolet rays are admitted (as against 5% for window glass). Glass fibers and crinkled surfaces diffuse infrared heat rays, making this material almost a perfect solution for greenhouse coverings.
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Light, as we have seen above, is the energizer for the primary growing process known as photosynthesis. The "white" light visible in the ultraviolet range of wavelength is actually made up of tones of violet, blue, green, yellow, orange and red; light projected through a prism will demonstrate this range of color. Scientists have for a long time been interested in the ultraviolet waves, known also as actinic rays. In fact, early Egyptians treated various diseases by exposing patients to the sun rays filtered through a blue quartz lens. Actinic rays are known as decomposing, or chemical rays, of the sun. They penetrate through solid matter and are thought to have the power of setting up a vibration, which, in matter that is susceptible to it, sets up a counter vibration.
Some of the actinic rays that shine through chlorophyll are absorbed. From plant-growing research that extends to 1880, we know that in photosynthesis, plants use more light from the blue and red parts of the spectrum. Little use is made of green, yellow, or other actinic nays . . . in fact, violet rays actually inhibit plant growth.
The accompanying graph was compiled from research data supplied in part by the Philips Research Laboratory, Eindhoven, Netherlands. Three processes are illustrated: carbon dioxide absorption, chlorophyll formation, and chlorophyll synthesis (photosynthesis). Carbon dioxide is absorbed into the plant through the stomata, located in the epidermis of leaves (oxygen is also transpired through the stomata). Stomata open under the influence of light, and are more widely open in the presence of blue light than either red or green. Evaporation and photosynthesis are intensified and chlorophyll production is accelerated when exposed to blue light.
Those of us living in mountainous apple country can testify to the effect that light plays in producing red pigment (anthocyanin) in apples. Ample amounts of late summer sunshine produce redder apples. A simple experiment can be performed to demonstrate the effect blue light has in producing anthocyanin: using a simple prism, project a solar spectrum on a green apple. The only part of the apple that will turn red is that in the blue and nearly ultraviolet end of the spectrum.
One greenhouse manufacturer (Lifelite Corporation, Concord, Calif.) promotes a bluish-red film colorant to absorb ultraviolet and green wavelengths. Red wavelengths are shifted and intensified. These self-adhering sheets can be used as reflectors from indoor fluorescent units, or on outdoor greenhouse panels. The degree of chlorophyll absorption under the influence of red light is significant, as illustrated in accompanying graph.
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