Testing Services:
Understanding the advantages and limitations of the available testing services requires a brief discussion of the nature of daylight and the significance of both quantitative and qualitative evaluation.
Visual Comfort and Measured Illumination:
Lighting criteria for building designs are often provided as numeric values reflecting a desired amount of illumination in a given space. Quality lighting design, involves more than putting the correct amount of light in a given location. It involves creating a productive and pleasant visual experience. It’s not just about “how much” but also about “how”. It is possible to put the correct amount of light into a space in a way that makes the space uncomfortable and entirely unusable. For this reason, effective daylight model testing not only considers the numerical results of measured daylight performance but also, using computer simulation, photography, videography and direct observation correlates this information with a qualitative consideration and evaluation of the resulting visual environment.
A Complex Sky:
Daylight is at the same time, a simple and complex phenomenon. The daylight that we take for granted as it reaches the earth and, in-turn, the inside of a building follows multiple paths on its journey from the sun to the interior of a space. For the purposes of daylight evaluation these multiple paths are characterized by type as different “sources” of daylight.
On a clear sunny day, some light travels directly from the sun into the interior of a building. This component is called “direct beam illumination” and is very intense and directional in nature. Direct beam daylight in a building is dramatically influenced by the angular position of the sun as it moves through the sky throughout the day month and year.
Under any weather conditions, some light also reflects off of the moisture in the atmosphere and causes the entire sky vault to “glow” with light. This component is called “sky vault illumination” and is very diffuse and variable. Sky vault illumination varies widely in amount, distribution and characteristic depending upon the weather and sky conditions at the time of consideration. Sky vault illumination is very different for pure sunny days compared to overcast days; partly cloudy and partly sunny days are different still and are particularly variable, dynamic and complex.
Still other light (both beam and sky vault) reflects off of adjacent objects and surfaces such as the ground, roof surfaces, nearby buildings and vegetation. This light source is called “ground reflectance illumination” and is highly dependent upon building geometry and the immediate site context. Various daylight model testing techniques are utilized to simulate the components of this complex mix of different daylight "sources".