Microwaves may be great at warming up food, but what about warming people? Using microwaves to directly heat owners of a room would save much of the energy wasted by heating walls and furniture. And despite popular ideas about microwaves, this technique would be safe, according to Charles R. Burlier of the Microwave Research Center in Marlborough, New Hampshire. Low-power microwaves only penetrate   the skin (low-power microwave penetration in a ham is about 0.2 inches, for example) and with no negative effects. To test this idea, Buffler subjected himself to microwaves in a special room using a standard 500-watt, 2459 MHz magnetron  . He found that a person will start to feel warmth at about 20 milliwatts per square centimeter (mw. / sq. cm. ) ; a satisfactory feeling of warmth occurs between 35 and 50mw. / sq. cm. By comparison, a person standing in noonday summer sun feels the amount of 85 mw. / sq. cm. And a frozen meat pie in your microwave oven receives about 1000 mw. / sq. cm. In houses of the future, each room could be provided with its own magnetron, says Buffler. When you stepped into the living room, for example, a motion detector  would turn on the magnetron, filling the room with low-power microwaves. In the same way that a microwave oven heats up a hamburger, but not the plate it's on, you would feel warmth from the microwaves without changing the temperature of your coffee table. (You could, however, make your favorite easy chair even more comfortable by treating it with a radiation-absorbing chemical.) While it might be some time before homeowners are comfortable enough with the idea to set up whole-body microwave heaters in houses, Buffler says microwaves may attract livestock  farmers. Lambs that are born outdoors in winter, for example, are frequently lost to cold. Microwaves could warm the lambs safely and quickly. The test conducted by Buffler shows that when a person feels comfortable warmth, he receives about   _  .
20 mw. / sq. cm. 40 mw. / sq. cm. 60 mw. / sq. cm. 85 mw. / sq. cm.