Solar Radiation (Sunshine)

MIL-STD-810G- METHOD 505.5

This method has two purposes:

  1. Determine the heating effects of direct solar radiation on equipment.

  2. Assist in identifying the actinic effects (photo-gradation) of direct solar radiation

Implementation

This method is used to evaluate equipment that may be exposed to solar radiation during its open life cycle in hot climates. This method is valuable in evaluating the effects of direct exposure to sunlight (solar spectrum and energy level at sea level). Procedure I is useful in determining the temperature rise (beyond the environment) of materials caused by solar charging. Although not designed for this, Procedure II can be used to simulate the ultraviolet effect of solar radiation at different locations and altitudes using different radiation sources that allow a reasonable comparison to measurements of these natural radiation conditions.

The heating effects of solar radiation differ from those of high air temperature alone, in that solar radiation produces directional heating and thermal color transitions. In the solar radiation test, the amount of heat absorbed or reflected depends mainly on the absorption or reflective properties of the surface close to the radiation  (e.g., roughness, color, etc.). If a glazing system (glass, clear plastic, or clear media) such as a windshield is part of the test item configuration, and the component is exposed to the solar energy that has passed through a glazing system, a full spectrum source is used.

 

In addition to the difference in expansion between different materials, changes in the intensity of solar radiation can cause components to expand or shrink at different rates that can cause severe stresses and loss of structural integrity. In addition to those identified in Method 501.5, consider the following typical problems to determine if this method is appropriate for the equipment being tested.

A partial list includes:

  • A blocking or releasing of moving parts

  • Weakening of the joints, soldering and glued parts

  • Changes in strength and flexibility

  • Loss of calibration or malfunction in attaching devices

  • Loss of sealing integrity

  • Changes in electrical or electronic components

  • Early actuation of electrical contacts

  • Changes in the properties of elastomers and polymers

  • Peeling, de-lamination of paints, composites, surface lamination with adhesives such as radar absorbent material

  • Softening of filler compounds

  • Pressure changes

  • Condensation from composites and explosives