Soft white incandescent lamps utilize a clear glass lamp envelope which has been coated with a fine transparent powder, usually silica, on its inside wall. The powder diffuses the light from the filament so that the eye cannot form a focused image of the filament. The silica powder does not alter the spectrum of the light emitted from the filament. Some light is lost due to reverse scattering by the silica powder.
Lamps known as "bugfoiler" lamps emit radiation in a range of wavelengths which is poorly seen by many insects. Prior art bugfoiler lamps have utilized a cadmium sulfide coating on the lamp envelope. The cadmium sulfide acts as a filter and attenuates wavelengths less than 500 nanometers more than wavelengths above 500 nanometers. Consequently, the radiation emitted by the lamp is primarily in a wavelength range above 500 nanometers. Such bugfoiler lamps are relatively inefficient, since the shorter wavelengths are unused. In addition, the cadmium sulfide coating is toxic.
The human eye is much more sensitive to wavelengths in the yellow portion of the spectrum than to wavelengths in the violet and blue portions of the spectrum. Thus, radiation emitted by an incandescent lamp in ultraviolet, violet and blue portions of the spectrum produces very little stimulation of the human eye.
Luminescent phosphors are widely used in fluorescent lamps to convert ultraviolet radiation to visible radiation. The phosphor is a coating on the lamp envelope. The phosphor absorbs radiation in one wavelength range and emits radiation in another wavelength range. To our knowledge, luminescent phosphors have not been used on incandescent lamps.
It is a general object of the present invention to provide improved incandescent lamps.
It is another object of the present invention to provide an incandescent lamp having a luminescent phosphor coating to alter the spectral distribution of radiation emitted by the lamp.
It is a further object of the present invention to provide incandescent lamps having high luminous efficacy.
It is yet another object of the present invention to provide improved lamps that are poorly seen by insects.