Patent Application
20100277056
1. Field of the Invention
The present invention is directed to a fluorescent lamp with a UV-blocking layer which protects a protective polymeric sleeve surrounding the lamp.
2. Description of Related Art
Fluorescent lamps are susceptible to breaking if dropped or bumped. Coatings and sleeves have been developed for fluorescent lamps which have two functions: 1) to absorb impacts and thus impart increased impact resistance to the lamp, to reduce breakage, and 2) to act as a containment envelope to contain shards or fragments of glass in case the lamp shatters. Often, these coatings and sleeves are subject to degradation from UV-light emitted from the fluorescent lamp. Such degradation causes the coatings and sleeves to develop yellowing or haze that partially blocks transmission of visible light. Moreover, such degradation causes the coatings and sleeves to become more brittle over time, so that they are less able to provide impact resistance and act as containment envelopes. As a result, over time, the fluorescent lamp becomes less protected from breakage and, if it does shatter, the glass fragments are less likely to be contained by an intact containment envelope. Accordingly, there is a need for a protective sleeve that is less susceptible to UV-degradation.
A sleeve-protected fluorescent lamp comprising a mercury vapor discharge fluorescent lamp surrounded by a sleeve. The fluorescent lamp comprises a light-transmissive glass envelope having an inner surface, a pair of electrode structures mounted inside said envelope, a first base sealing a first end of the lamp, a second base sealing a second end of the lamp, a discharge-sustaining fill comprising inert gas sealed inside said envelope, and a phosphor layer inside said envelope and adjacent the inner surface of the envelope. The sleeve comprises a layer of polymeric material. The sleeve-protected lamp further comprises a UV-blocking layer between the polymeric material layer and the glass envelope. The UV-blocking layer comprises a UV-blocking component of Al2O3 or ZnO or SiO2 or TiO2 or mixtures thereof. The inside diameter of the sleeve is at least 0.2 mm greater than the outside diameter of the lamp so that there is a gap between the lamp and the sleeve.
In the description that follows, when a preferred range such as 5 to 25 (or 5-25), is given, this means preferably at least 5 and, separately and independently, preferably not more than 25. UV light is generally considered to be 10-400 nm.
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The lamp 10 is hermetically sealed by bases 20 attached at both ends of the envelope 12. The electrode structures 16 are connected to pins 22 so that electric energy can be carried through the pins to the electrode structures 16. When the lamp 10 is energized, an electric arc is created between the electrode structures 16, the mercury is energized and emits UV light, and the phosphors in the phosphor layer absorb the UV light and re-emit light in the visible range. The barrier layer 24 permits visible light to pass through and functions to reflect UV light that has passed through the phosphor layer back into the phosphor layer where it can be utilized. Nonetheless, some UV light can escape out of the envelope 12 and potentially strike the protective sleeve 26.
Lamp 10 is preferably linear, such as 2, 3, 4, 6 or 8 feet long and preferably circular in cross section. Lamp 10 can be any diameter as known in the art, preferably ⅝, ¾, 1, 1¼ or 1½ inches in diameter, such as T5 to T12 lamps as known in the art. Lamp 10 is preferably a T8 or T12 lamp as known in the art.
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Layers 28 and 32 function to block transmission of UV light, which if transmitted, acts to degrade, cause yellowing, cause haze, and cause brittleness, of the outer layer 30. When the sleeve 26 is degraded, it is less able to protect the lamp from impact shattering and less able to contain glass fragments from flying off. The invention protects sleeve 26 from degradation, so the lamp is more shatter resistant and, if the lamp does shatter, there is better fragment retention.
Further details and benefits of the invention are illustrated in the following Example.
Two layers were tested for irradiance: 1. A conventional four foot linear fluorescent lamp (F32T8/SPX30) was coated on its outer surface with about 8 g of GUZ-140 from Nippan Kenkyujo (“Coated Lamp”). 2. A lamp the same as the Coated Lamp, but without the coating (“Bare Lamp”). Irradiance was measured with an Optronics Laboratories OL756 double monochromator calibrated with NIST traceable standards. The detector was placed 20 cm from the center of the lamp. The lamps were burned horizontally and run with reference photometry at line volts. The irradiance data for the Coated Lamp and Bare Lamp is given in Table 1. As can be seen, the coating was very effective in blocking UV radiation. The invented layers 28, 32 preferably permit not more than 5, 10 or 20 percent transmission at 300, 330, 350, 360, 380 and 390 nm after 50 hours of operation.
Although the hereinabove described embodiments of the invention constitute the preferred embodiments, it should be understood that modifications can be made thereto without departing from the scope of the invention as set forth in the appended claims.
