WO2006006097A2

WO2006006097A2 - Compact fluorescent lamp

Info

Publication number: WO2006006097A2
Application number: PCT/IB2005/052155
Authority: WO
Inventors: Rene J. Hendriks; Ludo V. M. Schreel; Ingrid J. M. Snijkers-Hendrickx
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-07-05
Filing date: 2005-06-29
Publication date: 2006-01-19
Also published as: WO2006006097A3

Abstract

A compact fluorescent lamp has a low-pressure mercury-vapor discharge lamp (1) surrounded by a light-transmitting envelope (60) which is attached to a lamp housing (70). The low-pressure mercury vapor discharge lamp has a light-transmitting discharge vessel (10) enclosing, in a gastight manner, a discharge space (11) provided with a filling of mercury and a rare gas. The discharge vessel comprises discharge means for maintaining a discharge in the discharge space. The discharge vessel is provided with a luminescent layer (17) comprising a luminescent material. A surface of the light-transmitting envelope (60) is provided with a light-refraction layer (61) comprising a UV-absorbing refractive material with a high refractive index. Preferably, the UV-absorbing refractive material is Ti02, Nb2O5, Ta2O5, ZrO, Si3N4, ATO, ITO, or FTO. Preferably, the light-transmitting envelope (60) is provided with a diffusion layer (65).

Description

Compact fluorescent lamp

The invention relates to a compact fluorescent lamp comprising a low-pressure mercury- vapor discharge lamp surrounded by a light-transmitting envelope which is attached to a lamp housing.

In mercury vapor discharge lamps, mercury constitutes the primary component for the (efficient) generation of ultraviolet (UV) light. A luminescent layer comprising a luminescent material may be present on an inner wall of the discharge vessel to convert UV to other wavelengths, for example, to UV-B and UV-A for tanning purposes (sun panel lamps) or to visible radiation for general illumination purposes. Such discharge lamps are therefore also referred to as fluorescent lamps. Alternatively, the ultraviolet light generated may be used for manufacturing germicidal lamps (UV-C). The discharge vessel of a low- pressure mercury vapor discharge lamp is usually circular and comprises both elongate and compact embodiments. Generally, the tubular discharge vessel of compact fluorescent lamps comprises a collection of relatively short straight parts having a relatively small diameter, which straight parts are connected together by means of bridge parts or via bent parts. Compact fluorescent lamps are usually provided with an (integrated) lamp cap. Normally, the means for maintaining a discharge in the discharge space are electrodes arranged in the discharge space. In an alternative embodiment the low-pressure mercury vapor discharge lamp comprises a so-called electrodeless low-pressure mercury vapor discharge lamp.

A compact fluorescent lamp of the type described in the opening paragraph is known from European Patent application EP-A 0 918 352. The known compact fluorescent lamp comprises a cover, a lighting circuit, an arc tube, a base, and a globe and is formed into a shape whose outline dimensions are nearly identical to the standard dimensions of a typical (incandescent) light bulb. The arc tube is comprised of a plurality of U-shaped bent bulbs. The globe may be transparent or milky white (diffusing layer). The globe is formed of glass, synthetic resin or the like into a smoothly curved shape nearly identical to the glass bulb of a typical (incandescent) light bulb. A drawback of the known low-pressure mercury vapor discharge lamp is that its UV output is still relatively high. The invention has for its object to eliminate the above disadvantage wholly or partly. According to the invention, a compact fluorescent lamp of the kind mentioned in the opening paragraph for this purpose comprises: a low-pressure mercury- vapor discharge lamp surrounded by a light- transmitting envelope which is attached to a lamp housing, the low-pressure mercury vapor discharge lamp comprising: a light-transmitting discharge vessel enclosing, in a gastight manner, a discharge space provided with a filling of mercury and a rare gas, the discharge vessel comprising discharge means for maintaining a discharge in the discharge space, the discharge vessel being provided with a luminescent layer comprising a luminescent material, a surface of the light-transmitting envelope being provided with a light- refraction layer comprising a UV-absorbing refractive material with a high refractive index. The light-transmitting envelope with a light-refraction layer comprising a UV- absorbing refractive material with a high refractive index reduces the UV output of the compact fluorescent lamp. With "high refractive index" is meant a refractive index which is high compared with the refractive index of the light-transmitting envelope. Normally, the light-transmitting envelope is made of a glass, a synthetic resin or the like with a refractive index typically lower than or equal to approximately 1.5.

Preferably, the UV-absorbing refractive material of the light-refraction layer is selected from the group formed by titanium oxide, niobium oxide, tantalum oxide, silicon nitride, cerium oxide, praseodymium oxide, tin-doped indium oxide, antimony-doped tin oxide, and fluorine-doped tin oxide. These materials have a relatively high refractive index compared with the material of the light- transmitting envelope. In addition, these materials exhibit good UV absorbing properties.

A preferred embodiment of the compact fluorescent lamp according to the invention is characterized in that the light-transmitting envelope is provided with a diffusion layer. The light-transmitting envelope with a diffusion layer renders the light emitted by the compact fluorescent lamp more uniform and homogeneous. In addition, the UV output of the compact fluorescent lamp is further reduced in that the light-transmitting envelope is provided with the high refractive index layer.

The compact fluorescent lamp according to the invention may be provided with a separate light-refraction layer and a separate diffusion layer. According to a preferred embodiment of the compact fluorescent lamp, however, the light-refraction layer and the diffusion layer are intermingled. Intermixing the light-refraction layer and the diffusion layer improves the adhesion of the layer.

In a favorable embodiment of the compact fluorescent lamp according to the invention, the light-refraction layer and the diffusion layer are provided at an inner surface of the light-transmitting envelope. In this manner both the light-refraction layer and the diffusion layer or the intermixed light-refraction and diffusion layer are or is well protected against touching by the customer during life of the compact fluorescent lamp.

A preferred embodiment of the compact fluorescent lamp according to the invention is characterized in that the light-refraction layer and the diffusion layer are provided on opposite sides of the light-transmitting envelope. In this configuration, the diffusion layer is preferably applied on an inner surface of the light-transmitting envelope and the light-refraction layer is applied on an outer surface of the light-transmitting envelope. Preferably, the light-refraction layer is a continuous layer applied on a surface of the light-transmitting envelope by a standard deposition method such as, for example, by dipping or spray coating. In an alternative embodiment, the UV-absorbing refractive material in the light-refraction layer is provided on small plates with a dimension in the range from approximately 1 to approximately 20 μm. Such small plates can be coated with a layer of the UV-absorbing refractive material. Preferably, the plates comprise phyllosilicate particles, preferably mica particles. Preferably, the phy Ho silicates are embedded in a matrix that forms the light- refraction layer.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawings:

Figure IA is a cross-sectional view of an embodiment of a compact fluorescent lamp according to the invention comprising a low-pressure mercury- vapor discharge lamp surrounded by a light-transmitting envelope which is attached to a lamp housing, and

Figure IB is a cross-sectional view of a detail of the wall of the light- transmitting envelope according to an embodiment of the invention. The Figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are strongly exaggerated. Similar components in the Figures are denoted by the same reference numerals as much as possible.

Figure IA schematically shows a compact fluorescent lamp comprising a low- pressure mercury vapor discharge lamp 1 surrounded by a light-transmitting envelope 60 which is attached to a lamp housing 70. The low-pressure mercury- vapor discharge lamp is provided with a radiation-transmitting discharge vessel 10 enclosing, in a gastight manner, a discharge space 11 having a volume of approximately 10 cm³. The discharge vessel 10 is a glass tube which is at least substantially circular in cross-section and whose (effective) internal diameter is approximately 10 mm. The tube is bent in the form of a so-called hook and, in this embodiment, it has a number of straight parts, two of which, referenced 31, 33, are shown in Figure IA. The discharge vessel 10 further comprises a number of arc-shaped parts, two of which, referenced 32, 34, are shown in Figure IA. An inner wall 12 of the discharge vessel 10 is provided with a luminescent layer 17 comprising a luminescent material. A protective layer (not shown in Figure IA) may be present between the inner wall 12 of the discharge vessel 10 and the luminescent layer 17.

The discharge vessel 10 is supported by a lamp housing 70 which, in the example of Figure IA, also supports a lamp cap 71 provided with electrical and mechanical contacts 73a, 73b, which are known per se. The discharge vessel 10 of the low-pressure mercury- vapor discharge lamp is surrounded by a light-transmitting envelope 60 which is attached to the lamp housing 70. The light-transmitting envelope 60 generally has a matt appearance. The discharge space 11 in the discharge vessel 10 does not only comprise mercury but also a rare gas, argon in this example. Means for maintaining a discharge are constituted by an electrode pair (not shown in Figure IA) arranged in the discharge space 11. Such an electrode pair, generally, is a winding of tungsten coated with an electron-emissive material, here a mixture of barium oxide, calcium oxide, and strontium oxide. Current supply conductors (not shown in Figure IA) issue from the electrode pair to the exterior of the discharge vessel 10. The current supply conductors are connected to an (electronic) power supply which is accommodated in the housing 70 and are electrically connected to the electrical contacts 73 a and 73b at the lamp cap 71. In Figure IA, a surface of the light-transmitting envelope 60 is provided with a light-refraction layer 61 comprising a UV-absorbing refractive material with a high refractive index. The light-transmitting 60 envelope with a light-refraction layer 61 comprising material with a high refractive index reduces the UV output of the compact fluorescent lamp. The light-refraction layer may alternatively comprise a stack of alternating layers with a high and a low refractive index. In the example of Figure IA, the light-refraction layer is provided on an outer surface of the light-transmitting envelope 60. Preferably, the UV-absorbing refractive material of the light-refraction layer 61 is selected from the group formed by titanium oxide, niobium oxide, tantalum oxide, zirconium oxide, silicon nitride, tin-doped indium oxide, antimony-doped tin oxide, and fluorine-doped tin oxide. Titanium oxide

(TiO₂) has an average refractive index of approximately 2.35-2.8 (at 550 nm); niobium oxide (Nb₂O₅) has an average refractive index of approximately 2.35 (at 550 nm); tantalum oxide (Ta₂O₅) has an average refractive index of approximately 2.18 (at 550 nm); zirconium oxide (ZrO₂) has an average refractive index of approximately 2.06 (at 550 nm); silicon nitride (Si₃N₄) has an average refractive index of approximately 1.9 (at 550 nm); praseodymium oxide (Pr₂O₃) has an average refractive index of approximately 1.75 (at 550 nm); tin-doped indium oxide (ITO) has an average refractive index of approximately 1.95 (at 550 nm). The use of the materials with high refractive indices as mentioned above results in a considerable reduction of the UV output of the compact fluorescent lamp. In the example of Figure IA, a surface of the light-transmitting envelope 60 is provided with a diffusion layer 65 for diffusing the light emitted by the low-pressure mercury vapor discharge lamp 1. Preferably, the diffusion layer 65 is a diffusely scattering layer comprising, by way of example, particles of titanium oxide, particles of silicon dioxide, and/or halophosphate particles. Another suitable material for the diffusion layer is a layer of aluminum oxide.

In the embodiment of the compact fluorescent lamp as shown in Figure IA, the light-refraction layer 61 and the diffusion layer 65 are provided on opposite sides of the light-transmitting envelope 60. In an alternative embodiment the light-refraction layer 61 and the diffusion layer 65 are intermingled. Intermixing of the light-refraction layer and the diffusion layer improves the adhesion of the layer.

In the embodiment of the compact fluorescent lamp as shown in Figure IA, an outer surface of the lamp housing 70 is also provided with the light-refraction layer 61.

Figure IB is a schematic cross-sectional view of a detail of the wall of the light-transmitting envelope 60 according to an embodiment of the invention. In this embodiment, the light-refraction layer 61 and the diffusion layer 65 are provided at an inner surface of the light-transmitting envelope 60.

Preferably, the light-refraction layer 61 is a continuous layer applied on a surface of the light-transmitting envelope 60 by a standard deposition method such as, for example, by dipping or spray coating. In an alternative embodiment, the UV-absorbing refractive material in the light-refraction layer 61 is provided on small plates with a dimension in the range from approximately 1 to approximately 20 μm. Such small plates can be coated with a layer of the UV-absorbing refractive material. The plates may also be coated with a stack of alternating layers with a high and a low refractive index. For coating the small plates with the UV-absorbing refractive material standard coating techniques are used such as, for example, spray deposition, chemical vapor deposition, or (reactive) sputtering.

Preferably, the plates comprise phy Ho silicate particles. Phyllosilicates form a subclass of the silicates and comprise rings of tetrahedrons linked by shared oxygen atoms to other rings in a two-dimensional plane, producing sheet-like structures. The typical crystal habit of the phyllosilicates is flat, platy, book-like and almost all members display a good basal cleavage. Very suitable members of the phyllosilicates are mica particles. The phyllosilicates are embedded in a matrix that forms the light-refraction layer. The matrix may be formed in various manners, for example comprising SiO₂ or a polymer material. Suitable matrix- forming materials are polyurethane, acrylic lacquers, and sol-gel type materials. Generally, the matrix-forming materials form scratch-free layers adhering well to the surface of the light-transmitting envelope.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. A compact fluorescent lamp comprising a low-pressure mercury- vapor discharge lamp (1) surrounded by a light-transmitting envelope (60) which is attached to a lamp housing (70), the low-pressure mercury vapor discharge lamp (1) comprising: - a light-transmitting discharge vessel (10) enclosing, in a gastight manner, a discharge space (11) provided with a filling of mercury and a rare gas, the discharge vessel (10) comprising discharge means for maintaining a discharge in the discharge space (13), the discharge vessel (10) being provided with a luminescent layer (17) comprising a luminescent material, a surface of the light-transmitting envelope (60) being provided with a light- refraction layer (61) comprising a UV-absorbing refractive material with a high refractive index.

2. A compact fluorescent lamp as claimed in claim 1, wherein the UV-absorbing refractive material of the light-refraction layer (61) is selected from the group formed by titanium oxide, niobium oxide, tantalum oxide, zirconium oxide, silicon nitride, cerium oxide, praseodymium oxide, tin-doped indium oxide, antimony-doped tin oxide, and fluorine- doped tin oxide.

3. A compact fluorescent lamp as claimed in claim 1 or 2, wherein the light- transmitting envelope (60) is provided with a diffusion layer (65).

4. A compact fluorescent lamp as claimed in claim 3, wherein the light-refraction layer (61) and the diffusion layer (65) are intermingled.

5. A compact fluorescent lamp as claimed in claim 3, wherein the light-refraction layer (61) and the diffusion layer (65) are provided at an inner surface of the light- transmitting envelope (60).

6. A compact fluorescent lamp as claimed in claim 3, wherein the light-refraction layer (61) and the diffusion layer (65) are provided on opposite sides of the light-transmitting envelope (60).

7. A compact fluorescent lamp as claimed in claim 1 or 2, wherein the UV- absorbing refractive material in the light-refraction layer (61) is provided on small plates with a dimension in the range from approximately 1 to approximately 20 μm.

8. A compact fluorescent lamp as claimed in claim 1 or 2, wherein the plates comprise phyllosilicate particles, preferably mica particles.

9. A compact fluorescent lamp as claimed in claim 1 or 2, wherein an outer surface of the lamp housing (70) is provided with the light-refraction layer (61).

10. A compact fluorescent lamp as claimed in claim 1 or 2, wherein the lamp housing (70) is provided with an integrated lamp cap (71).