Most glazing materials are manufactured to meet specific industry standards for strength and light transmission according to ASTM (Association of Standards and Test Methods) guidelines . The NGMA Glazing Standards lists various ASTM test procedures that apply to typical greenhouse glazing materials. There are tests recognized by the NGMA, including those for measuring light transmission, tensile strength, flexural strength, impact strength, and more. Most glazing materials are manufactured to meet industry standards for light transmission according to the Association of Standards and Test Methods (ASTM) guidelines. Some of the properties to consider in the selection of the glazing material include Photosynthetically Active Radiation (PAR), heat loss, thermal transmission, and life expectancy. There too are other factors are to be considered in the selection of the glazing material, such as maintenance and installation costs, budget, tax laws, and zoning regulations. Permits may be required, depending on local zoning and building codes as well as the type of glazing material. Plastic greenhouses may be considered temporary structures with lower taxes and fewer permit requirements than permanent buildings.

Photosynthetically Active Radiation (PAR) Transmission

Light transmission is the amount of light (solar energy) which is able to pass through a given substance of glazing material. Light transmission or solar energy can be objectively tested according to ASTM tests. The unit of measurement for light is nanometers (nm). The entire solar spectrum contains various ranges of light (i.e., UV, PAR, visible, infrared, etc.).

Direct and Diffused Radiation

Based on physical properties, surface orientation (angle of incidence), and the types of the glazing material, portions of the incoming light are either transmitted, reflected and/or absorbed. On a cloudless day, most sunlight travels in a straight path through the Earth’s atmosphere. Under these conditions, the incoming light is termed direct radiation. On a cloudy day, the sunlight is diffused by the many water vapor particles in the moisture-laden air. This light is called diffuse radiation. It is important to understand that diffuse radiation reaches the greenhouse surface from many different directions other than the direction of its source (the sun).

Heat Loss

The U-value is the measure of the amount of heat that the material will transmit through a material, such as greenhouse glazing and is measured in British thermal units per square foot per degree Fahrenheit per hour (Btu/ft2-°F-hr). (Here, a lower number is more desirable.) 0.35BTU/hr-ft2-F or lower is preferable.

Thermal Transmission

Thermal transmission is the ability of infrared (IR) radiation (heat) to travel through material and is particularly an issue in greenhouses on cloudless winter nights. Shortwave radiation from the sun passes through the glazing and heats the greenhouse plants, soil, and structures. As the plants, soil, and greenhouse structures become warmer than the surrounding temperature, they emit heat in the form of IR radiation.

Life Expectancy

The life expectancy of the glazing material is another important consideration. According to the NGMA, the usable life of glazing materials is defined as the number of months or years that a material will function effectively in a commercial growing application. To function effectively, the glazing material must retain some portion of its essential properties of strength and inherent light transmission. Specific ASTM test procedures exist for measuring longevity.

The diffuse glass and AR-coated diffuse glass produced by Yuhua have cooperated with many large commercial greenhouses in agriculture, horticulture, nurseries and experiments. We have cooperated with large greenhouse project companies such as Havecon, Van Der Hoeven, Kubo, etc. for many years. Yuhua greenhouse glass has a light transmittance of up to 99%, and haze 5/10/20/30/50/70/75 greenhouse diffuse glass is available!

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