the warmer air on the ceiling is pushed down along the walls and into the room, heating the cooler air. This avoids blowing a stream of air directly at the occupants of the room, which would tend to cool them. This action works to equalize, or even out the temperature in the room, making it cooler at ceiling level, but warmer near the floor. Thus the heating thermostat in the area can be set a few degrees lower to save energy while maintaining the same level of comfort. Though reversible models of industrial-grade ceiling fans do exist, most are not reversible. High ceiling heights in most industrial applications render reversibility unnecessary. Instead, industrial ceiling fans typically de-stratify heat by blowing hot air at ceiling level directly down toward the floor. Blade shape Residential ceiling fans, which are almost always reversible, typically use flat, paddle-like blades, which are equally effective in downdraft and updraft. Industrial ceiling fans typically are not reversible and operate only in downdraft, and therefore are able to make effective use of blades that are contoured to have a downdraft bias. More recently, however, residential ceiling fan designers have been making increasing use of contoured blades in an effort to boost ceiling fan efficiency. This contour, while serving to effectively boost the fan's performance while operating in downdraft, can hinder performance when operating in updraft. Air conditioning The most commonplace use of ceiling fans today is in conjunction with an air conditioning unit. Without an operating ceiling fan, air conditioning units typically have both the tasks of cooling the air inside the room and circulating it. Provided the ceiling fan is properly sized for the room in which it is operating, its efficiency of moving air far exceeds that of an air conditioning unit, therefore, for peak efficiency, the air conditioner should be set to a low fan setting and the ceiling fan should be used to circulate the air. Flicker and strobing Ceiling fans are usually installed in a space with other lighting fixtures, but if the fan is positioned too close to a light panel or fixture, a strobe or flicker effect may occur. A strobe or flicker effect is a phenomenon which occurs when light brightens and dims consistently as it penetrates and passes through a moving ceiling fan. This is due to the fan blades intermittently blocking the light, causing shadows to appear across