This invention relates to colored fluorescent lamps, and more particularly to colored fluorescent lamps that comprise an envelope and at least a phosphor coating and a barrier coating deposited on an inner surface portion of the envelope.
In certain applications of fluorescent lamps, for example in applications for entertainment purposes, a colored light other than a white one is desired. In case of conventional fluorescent lamps such as for example low-pressure fluorescent lamps, an outer covering layer on the envelope provides a color of the emitted light. A patent abstract published under No. JP 59217939 discloses a double envelope structure, in which the outer envelope is provided with a coloring layer on its inner surface. Though the environmental pollution in case of using such lamps is reduced, the manufacturing costs of an additional outer envelope are too high.
The glass material of the envelope, the tube or the bulb, which is basically transparent, can also be colored. This is too expensive, and only a few colors are accessible since only a few additive agents are capable of mixing with the glass material.
Another way of coloring the output light is to use a color filter or paint layer applied to the outer surface of the envelope. This requires a further step in the manufacturing technology and the resulted lamp is sensitive to mechanical impacts, such as scratches.
A further possible way of coloring fluorescent lamps is doping the phosphor by pigments. A possible solution is known, for example from patent abstract published under No. JP 58004243. A phosphor suspension is colored with an organic dye and the suspension is then applied to the inner wall of a glass tube of the envelope. The tube becomes colored after being dried. This and similar methods have a drawback that the colored phosphor suspension cannot be recycled in any customary manner.
When fluorescent lamps belonging to the state of art are manufactured, a barrier coating is usually applied to an inner glass surface of the envelopes, which is used for different purposes. These purposes are, for example, improving lumen maintenance, reducing mercury consumption, reducing light deterioration at the ends of the envelope, and for providing conductive additional starting aids. The barrier coating forms a barrier between the phosphor coating and the glass envelope. Fluorescent lamp barrier coatings typically comprise alumina or silica particles. These barrier coatings are quite thin, generally less than 1-0.5 micrometer of thickness. The barrier coating is highly transparent to visible light, while an amount of ultraviolet light is beneficially reflected back into the phosphor layer. The most important purpose of the barrier coating is to provide a chemically inert boundary between the phosphor layer and the glass material of the envelope. U.S. Pat. No. 5,602,444 shows an example for a barrier coating, which effectively reflects ultraviolet light back into the phosphor layer. Efficient reflection is highly desirable for improved phosphor utilization, which becomes particularly important when expensive rare earth phosphors are used.
U.S. Pat. No. 5,258,689 discloses a fluorescent lamp having two light-transparent coatings or layers of different refractive index disposed adjacent to each other and on the inner surface of the lamp glass envelope. This double layer barrier coating comprises particles of two different size ranges, which results in a reduced ability of the two layers structure to act as an optical interference filter. These two referred US patents however, do not provide hints for changing the color of the emitted light.
There is a particular need for a colored fluorescent lamp with a barrier coating that can be manufactured easily and cost effectively without any additional step in the usual manufacturing technology.
There is also a need for fluorescent lamps that can be manufactured with different colors of broad variety.
In an exemplary embodiment of the invention, a colored fluorescent lamp is provided. This colored fluorescent lamp comprises an envelope having an inner surface, means far providing discharge within the envelope, a discharge gas fill inside the envelope, a phosphor coating adjacent to the inner surface of the envelope, and at least a barrier coating between the inner surface of the envelope and the phosphor coating. The barrier coating comprises a blend of alumina and at least one coloring pigment.
The fluorescent lamps having such barrier coating do not need any new procedural steps in the course of manufacture. The necessary quantity of doping pigments is low, and consequently the manufacturing costs are only slightly higher than those of the conventional fluorescent lamps. At the same time, the available light colors cover a broad range.
The invention will now be described with reference to the enclosed drawings, where
The envelope 2 has an inner surface 8, onto which first a barrier coating 9 and then a commonly used phosphor coating 10 is deposited. It is known for a person skilled in the art that the barrier coating 9 as well as the phosphor coating 10 may be deposited by using a suspension of the material of these coatings. The barrier coating 9 is located between the inner surface 8 of the envelope 2 and the phosphor coating 10. This barrier coating 9 comprises a blend of alumina and at least one coloring pigment. In one embodiment, the coloring pigments are metal oxides. The total amount of the pigment or pigments is less than 5 weight percent with respect to a total weight of a barrier coating suspension in a preferable embodiment. Due to this amount of pigments, the coloring is inexpensive.
Referring now to
The lamp 11 has a layer structure similar to the layer structure of the lamp 1 in
In an exemplary embodiment, the at least one pigment in the blend is selected from the group of red, green, blue and yellow pigments. These pigments can for example be the following compounds: iron oxide, chromium-cobalt oxide, sodium-aluminum silicate, and nickel titanate. For stability reasons, the total amount of the pigments is preferably less than 5 weight percent with respect to a total weight of a barrier coating suspension.
In an embodiment, in which at least three different color pigments are present in the blend, the pigments provides the possibility of mixing color components and thus obtaining a wide variety of complex colors. The commonly used means for handling color components is the CIE chromaticity diagram. Referring now to
Example 1 relates to an exemplary embodiment of the invention with respect to electrodeless lamps.
The following four pigments were used in different electrodeless lamps:
These are pigments usually used for colored incandescent lamps. It is to be noted that several other pigment types can be used in order to create other colors.
The pigments were put into usual barrier coating suspension of Degussa Aeroxide C, and the suspension was applied to electrodeless lamps. Each pigment was used in an amount of 1 weight % with respect to the total weight of suspension. First the suspension was homogenized in ultrasonic bath, and then poured into the electrodeless bulbs with and without fluorine doped tin-oxide coating. A few seconds after pouring the suspension into the bulbs, they were put in drying position of a barrier coater apparatus. Subsequently, the bulb envelopes were processed as usual coated bulbs of electrodeless lamps.
Table 1 shows several colors created by a barrier coating and identified by their x, y color coordinates in a chromaticity diagram (CIE). The color measurement of the barrier coating was carried out after 4 hour burning.
Table 2 shows the same values after 500 hour burning.
Table 3 shows the photometry results of colored electrodeless lamps after different burning hours. Values in the columns refer to the colors of the pigments used, the obtained luminous output in lumens (Lm), the maintenance of this lumen value, the corrected color temperature (CCT) in K, the CIE x, y coordinates and the resulted wattage for the differently colored lamps, after different burning times.
The last two rows indicate relevant values of a white reference light source.
This invention may be used in any fluorescent lamps, such as for example linear fluorescent lamps, compact fluorescent lamps electrodeless compact fluorescent lamps that contain barrier coating.
This invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to one skilled in the art upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.