In prior U.S. Pat. No. 3,670,193, owned by the same assignee, a full spectrum lamp is disclosed which produces visible light at a given color temperature, 5500.degree. K. in the preferred embodiment, and has a high C.I.E. color rendering index (CRI) typically greater than 80 and balanced amounts of near and mid ultraviolet energy (UVA and UVB) with the total spectral output correlated to that which is found in natural daylight of the same color temperature.
The present invention is directed toward an improved phosphor blend for a lamp of this general type for producing the broad spectrum visible light and ultraviolet energy output correlated to that of natural daylight at the same color temperature and which is capable of producing higher initial lumen output and has better maintenance in that more light is delivered over the life of the lamp. Accordingly, the lamp of the present invention is directed to more efficient light production in a full spectrum fluorescent lamp with essentially equal quality as compared to prior art lamps, i.e., more lumens per watt, with the quality of the light output being maintained over the life of the lamp due to a reduction in color shift of the light output.