Allowing natural daylight into a building is a growing trend in today’s architecture. We all know the positive impact of natural light on our health and wellbeing, when compared to artificial lighting. Daylighting is almost becoming a requirement when designing residential units, schools, shopping centers, factories, offices, and practically any other building where people spend time.
Designers should be familiar not only with the light that we see with our eyes, commonly called visible light, but also with the rest of the solar spectrum which can be seen in the diagram below.
The Solar Spectrum
LT & SHGC Graph
One common consideration for designers is to allow natural light into the building, while controlling the amount of heat that comes in. This can be described as a ratio between light transmission (LT)* and solar heat gain coefficient (SHGC)** or shading coefficient. Very often, the requirement is to allow high visible light transmission, while maintaining low heat penetration or low SHGC. The below graph would show this requirement when advancing towards the upper left-hand side of the graph: lots of visible light (high LT) and less heat (low SHGC).
Palram has developed the Solar Smart™ range of colors in order to allow the phenomenon of “cool light” – a building environment that sees ample sun light without the heating of the so-called greenhouse effect.
*Light Transmission: Percentage of incident visible light that passes through an object.
**Solar Heat Gain (SHGC): The percent of incident solar radiation transmitted by an object which includes the direct solar transmission plus the part of the solar absorption reradiated inward.
Does SHGC impact U-Value and thermal insulation?
The solar properties such as light transmission, solar heat gain coefficient (SHGC) or shading coefficient are not directly related to U-value but all the parameters play an important role when considering the energy efficiency of a building or part of it.
U-value or R-value measure thermal transmittance, which is basically how fast heat would be transferred through a material such as concrete, wood, glass and so on. When a material provides good thermal insulation, heat will move slowly through that material, and the U-value would be low. U-value measurements are applicable to transparent or opaque building materials and in fact to any material.
SHGC and other solar measurements are relevant to transparent materials such as glass, polycarbonate and acrylic. SHGC represents the fraction of the solar radiation that enters the building through a transparent opening in the roof or wall. A lower SHGC would mean that less solar radiation enters the building and there is more of a shading effect. Lower SHGC’s can be achieved using colors and other additives that absorb the heat or reflect it away. In hot climates, one might look for a lower SHGC to avoid the heat buildup from the shining sun. In cold climates, solar radiation can actually be beneficial in saving heating costs, so a higher SHGC might be desired.
To summarize, when considering the energetic efficiency of a building, there is always a need to consider thermal performance of the building’s fabric, typically using the U-Value. Whenever light transmitting openings such as windows, skylights or sidelights are involved, SHGC becomes the other crucial element to consider since solar radiation, for good or bad, impacts the building’s energy usage for heating, air conditioning and illumination. Different products have different thermal properties and it is important to choose the most appropriate product for your building. Contact Palram with your requirements and we will advise you on the best solution.