When it comes to windows that face the south in the northern hemisphere, however, there is an even bigger challenge to consider. During winter, the sun remains low in the sky, with its light shining more directly on south-facing windows for longer periods of time than in summer. This allows for a unique situation where applied graphics, most notably dark colored graphics, can absorb the heat of the sun more dramatically than at other times of the year. This is especially problematic in the morning when air and glass temperatures are at the coldest of the day. Dramatic temperature differentials across the face of the glass can be generated on bright cold mornings depending on the color of the graphics. Furthermore, since graphics are typically installed in the evening after stores close, the temperature differential from morning to afternoon is much greater (roughly -10°F to 50°F sunup to sundown in winter vs. 60°F to 90°F in summer). That’s a difference of 60°F vs. 30°F — twice the change.
If there are large areas of dark colors in the graphic, this effect is magnified because they absorb more light and heat than lighter colors, causing them to rise to significantly higher temperatures. Think of the seats you wouldn’t want to sit on wearing shorts on a hot summer day. The heat causes the glass in the areas with dark graphics to expand — referred to as “thermal absorption” — which can cause piping and peeling of the graphic in those areas. If the graphic gets hot enough, it can even cause the glass to crack. A complaint arising from such issues is quite often assumed to be a printing or installation issue; however, it’s much more likely that large areas of dark colors are to blame. This is especially true if those areas are located at the bottom of the window where it gets virtually no shade. This is seen most often with dark red, purple, blue and black.