Tiny signal lamps on outdoor transformers atop power-line poles, barely noticeable when street lights are turned on, were found glowing brightly in a blackout and had to be concealed from possible enemy planes. In answer to a rush call from the Pacific coast, engineers of the Westinghouse company designed a helmetlike cap which, when placed over the lamp, permits a narrow beam to shine downward but cannot be seen from above. In normal conditions the lamp is turned off, coming on only as a warning for the service man if the transformer is becoming overheated.