Abstract Ti02 is included as a constituent in the soda-lime silicate glass envelope of a fluorescent lamp in an amount sufficient to chemically stabilize the glass an thus permit the use of a thinner phosphor coating without decreasing the light output of the lamp or impairing its lumen maintenance. Up to 10 percent by weight Ti02 is employed and less than 2 percent by weight is preferred to minimize lamp cost. The Ti02 also inhibits solarization and the resultant darkening of the envelope under the influence of the impinging ultraviolet radiations generated within the lamp during operation. With 1.25 percent by weight Ti02 in the glass, the amount of phosphor required per lamp is reduced by 30 percent without decreasing the light output or lumen maintenance. In the case of calcium halophosphate type phosphor, the phosphor weight per lamp is reduced by 40 percent without impairing the lumen maintenance and with only a slight drop in light output compared to a conventional lamp utilizing the same type of phosphor.
The fluorescent lamp of claim 1 wherein; said envelope is of tubular configuration, approximately 4 feet long and has an outer diameter of approximately 1 1/2 inches, and the total amount of phosphor on the inner surface of said envelope varies according to the average particle size of the phosphor particles and, for phosphor having a given average phosphor particle size within said range of from about 5 to 17 microns, lies within the hatched area Z of the graph shown in FIG. 8.
Claim 2
Dependent Claim
225 words
A fluorescent lamp comprising, in combination; a light-transmitting envelope comprising soda-lime silicate glass that contains a predetermined amount of Ti02 up to about 10 percent by weight, mercury and an ionizable fill gas sealed within said envelope adapted to sustain a gaseous discharge that generates ultraviolet radiation when the lamp is energized, and a light-transmitting coating of phosphor on the inner surface of said envelope comprising a substantially uniform layer of finely-divided phosphor particles that have a predetermined average particle size within a range of from about 5 to 17 microns and emit visible radiation in response to impinging ultraviolet radiation generated by said discharge, the amount of phosphor per square centimeter of envelope surface being generally proportional to the average size of said phosphor particles and being within a range that has a lower limit of from about 1.1 to 1.8 milligrams per square centimeter for a phosphor having an average particle size of 5 microns and an upper limit of from about 5.3 to 8.3 milligrams per square centimeter for a phosphor having an average particle size of 17 microns, and the amount of Ti02 in said glass being sufficient to inhibit solarization of the glass and the formation of blackening deposits at the phosphor-glass interface due to chemical reaction between the mercury within the envelope and the alkali constituents of the glass.
Claim 3
Dependent Claim
68 words
The fluorescent lamp of claim 3 wherein; said envelope is of tubular configuration, is approximately 4 feet long and has an outer diameter of approximately 1 1/2 inches, and the total amount of phosphor on said coated envelope for a given average phosphor particle size within said range of from about 5 to 17 microns lies within the hatched area Z of the graph shown in FIG. 8.
Claim 4
Dependent Claim
27 words
The fluorescent lamp of claim 4 wherein; said soda-lime silicate glass contains less than about 2 percent by weight Ti02, and said phosphor is a halophosphate phosphor.
Claim 5
Dependent Claim
25 words
The fluorescent lamp of claim 5 wherein; said soda-lime silicate glass contains about 1.25 percent by weight Ti02, and said halophosphate phosphor comprises calcium halophosphate.