Electric Appliances & Apparatus
Diagram [on left] shows clear bulb in Convergent Beam Reflector. "X" is "spilled heat" spread outside the control of the reflector, and thereby lost. Whether reflector is shaped for parallel, divergent or convergent heat rays, same[sic] condition of "heat spill" holds true when the clear type of heat lamp is used.
Silver ring [on right] on the "bullseye" type of heat lamp eliminates "heat spill" by bringing within the control of the reflector all heat rays except those that come directly down to the heating area. The result is that what were formerly spilled and wasted heat rays are now collected, reflected down to the heat area, and put to practical use for heating.
see heat lamp 012.018
Original Caption by Science Service