Some recent 'breakthroughs' look a lot like some old technology that works just fine to keep cars and solar cells cool. What would you do if you had a "perfect mirror" -- one that would reflect nearly 100 percent of the incident light at any angle of incidence? Would you build a better solar collector? Make a windshield coating that would reflect the heat from the sun, keeping your car cooler? Develop a coating to reflect the ultraviolet and infrared light away from a solar cell to improve its efficiency? A recent development at the Massachusetts Institute of Technology has generated considerable excitement about this type of potential application. Those who wish to use the technology should understand that "perfect mirrors" are not entirely new but have been around for many years. In fact, coating designers who are developing this type of application and think they need this kind of mirror can probably adapt traditional quarter-wave stack reflector technology to solve their problems.