The Science of Shade
The shade that your patio screens and awnings creates does a lot to battle the sun. These are the areas where sunlight and UV rays have trouble penetrating the surfaces that the come in contact with.
What is shade?
Shade or a shadow is the absence of light in a space in which light is obstructed by an object. Few objects are solid enough to block out the light required for blackout conditions. Most shade is not a complete absence of light but a severe reduction in the amount of light able to reach the area.
A small point of light creates a simple shadow called an umbra. You can see an umbra when you shine a flashlight on an opaque object and it casts a shadow. The shadow begins and ends and, depending on the distance from the object, creates a sharp silhouette that closely resembles the form of the original object.
Larger light sources like the sun provide light from afar that is diffuse. Diffuse light is light that is not centralized into a single beam. Its energy is spread throughout a large area.
Light from large light sources creates several types of shadows:
The penumbra is the area around the darkest part of the shadow where diffuse light begins to penetrate the shadowed area. It has a medium level of light intensity and provides noticeable temperature changes.
The anumbra is the area where the length of the ends and begins to fade into the light area. It corresponds with the top of the opaque object. The anumbra extends past the top of the shadow and gradually lets in more light.
How does shade change throughout the day?
The angle of the sun affects the length and sharpness of shade. When the day begins, the sunlight is extremely diffuse. As it passes the horizon and moves toward the top of the sky, shadows become shorter and sharper.
At midday, shadows are cast directly downward. At this time, only suspended objects such as awnings will create shade.
How does shade affect temperature?
Standing in direct sunlight exposes you to solar radiation, which makes the air feel 10-15 degrees warmer than the actual temperature.
Temperatures are closer to actual air temperatures when you’re in the shade. Staying out of the solar radiation also prevents your skin from being damaged by too much sunlight, which can intensify the feeling of heat on the skin.