WO2020069724A1

WO2020069724A1 - Linear led light source

Info

Publication number: WO2020069724A1
Application number: PCT/EP2018/076688
Authority: WO
Inventors: James Hooker; Frank Broeders; Walter Schaaf
Original assignee: Flowil International Lighting (Holding) B.V.
Priority date: 2018-10-01
Filing date: 2018-10-01
Publication date: 2020-04-09

Abstract

The present invention provides a linear LED light source, comprising: a sealed lamp envelope (11); at least one LED unit (12) arranged inside the sealed lamp envelope (11); wherein the lamp envelope (11) is filled with a gas filling consisting of a thermally conductive gas of low atomic mass, preferably hydrogen or helium, containing fewer than 50,000 ppm (parts per million) of impurities, preferably fewer than 10,000 ppm, more preferably fewer than 1,000 ppm, further more preferably fewer than 100 ppm.

Description

Linear LED Light Source

Description

The present invention relates to a linear LED light source.

The present invention specifically relates to a linear LED light source in which LED units are linearly arranged in an elongated, substantially cylindrical translucent lamp envelope, such as a glass tube. The present invention is applicable to conventional linear LED light sources in which multiple LEDs are used in the LED units, as well as to linear LED filament light sources.

LED filament light sources such as LED filament lamps or LED filament light bulbs produce light by LED filaments - multi-diode structures that resemble the filament of an incandescent light bulb. The LED filaments consist of multiple LEDs connected in series on a transparent substrate, allowing the light emitted by the LEDs to disperse evenly and uniformly. A coating of yellow phosphor in a resin binder material converts the blue light generated by the LEDs into white light. An example for a LED filament light source is disclosed in US 8,400,051 B2.

LED filaments are also used for linear LED light sources that have a translucent lamp envelope of essentially cylindrical shape and a plurality of LED filaments arranged along the longitudinal axis of the lamp envelope. When conventional linear LED filament light sources are produced in linear configuration and operated in a vertical burning position, it has been identified that these lamps tend to suffer premature failures.

In light of this, it is an object of the present invention to provide a linear LED light source with good radiation characteristics and improved lifetime that is particularly suitable to be operated in vertical burning positions for a long period of time.

The above object is solved by a linear LED light source according to the subject- matter of claim 1. Preferred embodiments of the invention are indicated by the subject-matter of the dependent claims. Specifically, the present invention provides a linear LED light source comprising :

- a sealed lamp envelope;

- at least one LED unit arranged inside the sealed lamp envelope; wherein the lamp envelope is filled with a gas filling consisting of a thermally conductive gas of low atomic mass containing fewer than 50,000 ppm (parts per million) of impurities, preferably fewer than 10,000 ppm, more preferably fewer than 1,000 ppm, further more preferably fewer than 100 ppm.

A core aspect of the present invention is the usage of a single component gas filling with a very high chemical purity. Surprisingly, it has been found that the premature failure of conventional linear LED light sources, particularly linear LED filament light sources, can be attributed to properties of the gas filling of the lamps. The gas filling preferably consists of hydrogen or helium with the specified high chemical purity.

Prior art LED filament light sources are typically filled with a heat conductive gas filling comprised of a helium or hydrogen mixture that contains more than

5,000 ppm of other gaseous impurities, especially after operating for some hours.

The reason for these failures has been attributed to the vertical segregation of the different gases along the length of the linear light source. The gases having superior thermal conductivity tend to accumulate at one end of the glass tube, while the gases having inferior thermal conductivity accumulate at the other end of the glass tube and result in the LED filaments in the vicinity of those filaments operating at elevated temperature which compromises both their photometric performance and lifetime.

Using a single component gas filling with a high chemical purity according to the invention overcomes these problems, so that a linear LED light source with improved lifetime is provided that can be operated in a vertical burning position for long periods of time. Particularly, the linear LED light source according to the present invention can be operated in any burning position and be driven at a power density greater than 5 Watts per linear foot of lighted length (or approximately 800 lumens per foot or higher). The high chemical purity of the gas filling should be maintained throughout the lifetime of the linear LED light source. For this reason, the sealed lamp envelope is provided. The sealed lamp envelope is preferably hermetically sealed and made of a material that is impermeable to gases of low atomic mass. It is particularly preferred that the sealed lamp envelope is manufactured from a glass,

particularly a soft glass and hermetically sealed, e.g. by glass fusion, in order to ensure a gas-tight enclosure for the gas filling.

As material of the sealed glass envelope, a high purity version of ordinary soda- lime silicate is preferred. Particularly preferred is a high purity version of ordinary soda-lime silicate with low iron oxide content. A particularly preferable choice for the material of the sealed glass envelope is a soda lime silicate soft glass with high alkaline content, consisting of 69-75 wt% of Si0₂, 14-19 wt% of Li₂0, Na₂0 and/or K₂0, 6-10.5 wt% of MgO, CaO, SrO and/or BaO, 1.5-3 wt% of Al₂0₃ and/or B₂0₃, the remainder being unavoidable impurities. Such glass is favorable due to a low working temperature of around 1300 K and a high coefficient of linear expansion in the range of 85-90 · 10 ⁶ K ¹.

It is preferred that the sum of the contents of oxygen, nitrogen, argon and hydrocarbon vapours in the gas filling is 50,000 ppm or lower, preferably

10,000 ppm or lower, more preferably 1,000 ppm or lower, further more preferably 100 ppm or lower. These gases are particularly deleterious for the lifetime expectancy of the LED units, so that a reduction of their content below the specified value improves the lifetime of the linear LED source.

In a preferred embodiment, the at least one LED unit is constituted by a LED filament. The present invention has been motivated in the context of LED filament light sources. It should be emphasised that the present invention is also applicable to conventional linear LED light sources in which the LED units are constituted by LEDs of all types of packages mounted on a printed circuit board or an equivalent carrier and arranged inside the sealed lamp envelope. However, LED filaments are preferable due to their favorable omnidirectional light emission pattern and the present invention is particularly useful for linear LED light sources with LED filaments.

It is further preferred that the sealed lamp envelope is constituted by a tube of essentially cylindrical form, and that the LED units are sequentially arranged along the longitudinal axis of the sealed lamp envelope. With this configuration, the light emission characteristics of the linear LED light source can be improved, since substantially the entire length of the cylindrical tube can be used for emitting light.

It is further preferred that the linear LED light source has a length to diameter aspect ratio of at least 20: 1. Furthermore, it is preferable that the internal diameter of the sealed glass envelope is 15 mm or less. Linear LED light sources with this geometry are preferred for their emission characteristics and

compatibility to existing sockets for conventional light tubes. The operation of linear LED light sources with such a geometrical configuration in a vertical burning position is enabled by using the high purity filling according to the present invention. It is further preferred that the linear LED light source has a length to diameter aspect ratio of at least 10: 1, still more preferably of at least 5: 1.

It is further preferred that the LED units are disposed along substantially the entire length of the sealed lamp envelope. This further improves the radiation characteristics of the linear LED light source. Specifically, it is preferred that the distance between the ends of the sealed lamp envelope and the respective LED unit nearest to said end of the sealed lamp envelope is smaller than twice the diameter of the sealed lamp envelope.

In a further preferred embodiment, the LED units are mounted to support frames that are configured to conduct electric power for driving the LED units. Thus, the support frames serve two functions: on the one hand, a mechanical stabilisation of the arrangement of the LED units that serves to increase the mechanical robustness of the linear LED light source, on the other hand, providing a conductive pathway for the electric power required to drive the LED units. Since the mount frame serves two functions, the number of parts required for the linear LED light source can be reduced, which aids in improving the radiation

characteristics of the linear LED light source, because less components that may block part of the radiation emitted by the LED units has to be arranged in the sealed lamp envelope.

The support frames are preferably made from a metallic material with good conductivity and are preferably manufactured from wires, preferably with a diameter of 1.5 mm or less, to reduce blockage of emitted light. The cross- sectional shape of the support frames is not particularly limited and may be circular. Alternatively, the support frames may be manufactured from metal strips or sheets having a non-circular cross section to further limit optical shadowing and increase mechanical strength.

It is preferred that the metallic support frames are manufactured from an alloy and with a diameter such that they have an electrical resistance R/l between 50 itiW/m and 200 itiW/m. Conventionally, steel wires are used for the support frames of LED light sources. However, steel wires are characterised by a high electrical resistance, which causes an unfavorable voltage drop, leading to current imbalances between the different LED units. Using an alloy with the above-mentioned properties for the metallic support frames greatly reduces electrical resistance, which allows the diameter of the wires to be minimised and the luminous flux and efficacy of the linear light source to be maximised.

The electrical resistance R/l as defined in the context of this invention denotes electrical resistance per length unit with the unit itiW/m (milliohms per metre). It is calculated from the specific electrical resistance or electrical resistivity of the used alloy, p, which is a material specific constant and usually given in units of W-m (ohm-metres) at a temperature of the alloy of 20°C, and the cross-sectional area A of the metallic support frame, which is usually expressed in mm², according to the formula

R ₌ p

l A

With support frames having the characteristics according to the present invention, the voltage drop in the LED units can be dropped to acceptable levels of less than approximately 100 millivolts per metre. Thus, a linear LED light source with considerably greater length than in the prior art can be

manufactured.

Preferably, the metallic support frames are manufactured from an alloy and with a diameter such that they have an electrical resistance between 50 itiW/m and 150 itiW/m, more preferably 90 itiW/m to 120 itiW/m. It is preferred that the metallic support frames are manufactured from nickel or a nickel alloy, preferably a nickel-manganese alloy. These alloys have a very low specific electrical resistance and favorable mechanical properties.

Materials such as copper and its alloys are known to be used as materials for the wiring in electric lamps, and specifically for the tracks of printed circuit boards to which traditional LEDs are normally attached. However, copper is a very soft metal which is not mechanically robust, and which is also very difficult to attach to the LED filaments by conventional techniques such as resistance welding.

Nickel and its alloys overcome these problems, providing a metal alloy with low specific electrical resistance, high mechanical stability and good weldability. The high mechanical stability enhances the reliability of the linear LED light source, since the support frame is less prone to breaking.

Preferably, the metallic support frames are manufactured from a metal alloy that consists of 1 to 3 wt% manganese (Mn), preferably 2 wt% manganese (Mn), the remainder being nickel (Ni) and inevitable impurities. This alloy has been found to be specifically suitable due to its good mechanical and welding properties along with favorably low values for the electrical resistance R/l that can be achieved with such alloys.

Preferably, two support frames are provided, each being conductively connected to an electrical contact of the linear LED light source. Preferably, the LED units are connected between the support frames in parallel. This allows operating the LED units in parallel. With this, the voltage for operating the linear LED light source can be greatly reduced. However, the scope of this invention should not be limited to lamps having parallel-connected filaments.

It is further preferred that the light source mount assembly comprises buffer springs that are configured to support the support frames against the inner wall of the sealed lamp envelope. With this, the mechanical stability of the linear LED light source and thus its lifetime can be improved.

In a further preferable embodiment, the light source mount assembly comprises isolating bridges that are provided between the support frames and are configured to maintain a fixed relative position between the metallic support frames. This serves to further improve the mechanical stability of the light source mount assembly. Preferably, the isolating bridges are arranged adjacent to the proximal and distal ends of the sealed lamp envelope, respectively. Thus, the isolating bridges can support the mechanical stability of the light source mount assembly whilst minimising the blockage of emitted light.

The above and further features and advantages of the invention will become more readily apparent from the following detailed description of preferred embodiments of the invention with reference to the accompanying drawings, in which like reference signs designate like features, and in which:

Fig. 1 shows a schematic view of a linear LED filament light source

according to an embodiment of the present invention;

Fig. 2 is a schematic view of the linear LED filament light source of Fig. 1 in which relevant dimensional parameters are specified.

Fig. 1 is a schematic view of a linear LED light source according to an

embodiment of the present invention. The linear LED light source comprises a sealed lamp envelope 11 of essentially cylindrical shape that is translucent and made of glass. A light source mount assembly is arranged inside the sealed lamp envelope 11. In the present embodiment, the light source assembly comprises multiple LED units 12 mounted to metallic support frames 13a, 13b optionally via metallic spacer components 14, isolating bridges 15 and buffer springs 16.

The LED units 12 of the present embodiment are constituted by LED filaments.

The LED units 12 are sequentially aligned along the longitudinal axis of the sealed lamp envelope 11 and disposed essentially along the entire length of the sealed lamp envelope 11.

The light source assembly 10 is connected to an electrical feedthrough

component 17. Specifically, the metallic support frames 13a, 13b are conductively connected, e.g. welded or soldered to the electrical feedthrough component 17.

The metallic support frames 13a, 13b which carry the LED units 12 are supported against the inner wall of the sealed lamp envelope 11 by buffer springs 16 which serve to maintain the LED units 12 and the support structure of the support frames 13a, 13b and the optional metallic spacer components 14 along the axis of the sealed lamp envelope 11. They also serve to prevent physical damage by absorbing mechanical shocks that may be experienced during handling and transportation of the linear LED light source.

The optional metallic spacer components 14 may serve to orientate the LED units 12 in a particular mechanical configuration - in the present embodiment, in a linear configuration extending over the most part of the length of the sealed glass envelope 11. However it will be appreciated that many different mechanical configurations of the LED units 12 are possible, which may or may not require the utilisation of metallic spacer components 14. In order to further stabilise the assembly of the LED units 12 and metallic spacer components 14 two electrically isolating bridges 15 are provided near the respective ends of the sealed lamp envelope 11 to maintain a fixed relative position between the metallic support frames 13a, 13b, and may also optionally be provided at intermediate locations.

The isolating bridges 15 may be formed, for instance, from a dielectric material such as glass or ceramic bearing electrically isolated metallic wires for convenient welding to the support frames 13a 13b. The buffer springs 16 may be combined into the same physical assembly as the isolating bridges 15, as can be seen at the right end of the sealed lamp envelope 11.

The sealed lamp envelope 11 may optionally be capped by bases 19 at one or both ends. The left base 19 is equipped with electrical contacts 17a that are connected to the electrical feedthrough components 17. The bases 19 are attached to the sealed lamp envelope 11 by an adhesive 19a. Although Fig. 1 depicts a linear LED light source with a pair of electrical contacts 17a at the same end of the linear LED light source, it should be noted that the electrical contacts 17a may also be arranged with one electrical contact 17a at each end of lamp, or with a plurality of electrical contacts 17a at both ends of the lamp..

The electrical feedthrough components 17 electrically connect the light source mount assembly 10 to the exterior of the sealed lamp envelope 11. The electrical feedthrough components 17 are hermetically sealed into the sealed lamp envelope 11 in a gas-tight fashion of sufficient quality to avoid leakage of the low atomic mass gas filling 18. Electric power is fed to the linear LED light source via the electrical contacts 17a, through the electrical feedthrough components 17 to the metallic support frames 13a, 13b. If present, the metallic spacer components 14 are connected to the metallic support frames 13a, 13b and provide a conductive connection between the metallic support frames 13a, 13b and the LED units 12. Alternatively the LED units 12 may be connected directly to the metallic support frames 13a, 13b without the use of intermediate metallic spacer components 14. The metallic spacer components 14 and LED units 12 are arranged such that the LED units 12 are connected in parallel between the metallic support frames 13a, 13b.

Thus, the metallic support frames 13a, 13b and the metallic spacer components 14 not only serve not only serve as mechanical support frame for the LED units 12, but also as supply conductors via which electrical power supplied from the electrical contacts 17a is fed to the LED units 12.

The lamp envelope 11 is filled with a thermally conductive gas filling 18 consisting of a gas with of low atomic mass, such as hydrogen or helium. The gas filling 18 is a single component gas, preferably either hydrogen or helium. The single component gas filling 18 contains fewer than 50,000 ppm of impurities, preferably fewer than 10,000 ppm, more preferably fewer than 1,000 ppm, further more preferably fewer than 100 ppm.

Fig. 2 serves to illustrate relevant dimensional parameters of the linear LED light source of Fig. 1. The outer diameter of the sealed glass envelope 11 and, thus, of the linear LED light source, is denoted by d. The inner diameter of the sealed glass envelope is denoted by d,. L designates the length of the linear LED light source, excluding the protruding electrical contact pins as is standard practice.

As can be seen in Fig. 2, the light-emitting source constituted by the sequentially arranged LED units 12 extends substantially over the entire length L of the linear LED light source. More precisely, the distance between the inner ends of the sealed glass envelope 11 and the nearest LED unit 12 is smaller than twice the outer diameter of the sealed lamp envelope 11. Thus, the length of the non- radiating zones at each end of the linear LED light source does not exceed two times the outer diameter d of the linear LED source. According to the present embodiment, the sealed glass envelope 11 has a length L to diameter d aspect ratio of at least 20: 1. The inner diameter d, is chosen to be 15 mm or less. With the single component high purity gas filling 18, the linear LED light sources according to the present invention can be operated in any burning position and be driven at a power density greater than 5 Watts per linear foot of lighted length (or approximately 800 lumens per foot or higher), without suffering problems of premature failures.

The present invention has been motivated in the context of LED filament light sources. It is, however, emphasised that the present invention is also applicable to conventional linear LED light sources in which the one or more LED units 12 are constituted by LEDs mounted on a printed circuit board or an equivalent carrier and arranged inside the sealed lamp envelope 11. The one or more LED units 12 may also be constituted by LED packages as defined in the International Electrotechnical Vocabulary (IEC 60050). According to this definition, a LED package is an electric component comprising at least one LED die, and can include optical elements, light converters such as phosphors, thermal, mechanical and electric interfaces, as well as components to address ESD concerns.

List of Reference Signs

11 sealed lamp envelope

12 LED light source

13a, 13b metallic support frame

14 metallic spacer component

15 isolating bridge

16 buffer spring

17 electrical feedthrough component

17a electrical contact

18 gas filling

19 base

19a adhesive L length d outer diameter di inner diameter

Claims

1. Linear LED light source, comprising :

- a sealed lamp envelope (11);

- at least one LED unit (12) arranged inside the sealed lamp envelope

(11); wherein the lamp envelope (11) is filled with a gas filling (18) consisting of a thermally conductive gas of low atomic mass, preferably hydrogen or helium, containing fewer than 50,000 ppm of impurities, preferably fewer than 10,000 ppm, more preferably fewer than 1,000 ppm, further more preferably fewer than 100 ppm.

2. Linear LED light source according to claim 1, wherein the sum of the

contents of oxygen, nitrogen, argon and hydrocarbon vapours in the gas filling (18) is 50,000 ppm or lower, preferably 10,000 ppm or lower, more preferably 1,000 ppm or lower, further more preferably 100 ppm or lower.

3. Linear LED light source according to claim 1 or 2, wherein the at least one LED unit (12) is constituted by a LED filament.

4. Linear LED light source according to any of the preceding claims, wherein the sealed lamp envelope (11) is constituted by a tube of essentially cylindrical form, and wherein the LED units (12) are sequentially arranged along the longitudinal axis of the sealed lamp envelope (11).

5. Linear LED light source according to claim 4, wherein the linear LED light source has a length (L) to diameter (d) aspect ratio of at least 20 : 1.

6. Linear LED light source according to claim 4 or 5, wherein the internal diameter (d,) of the sealed glass envelope (11) is 15 mm or less.

7. Linear LED light source according to any of the preceding claims,

particularly to one of claims 3 to 5, wherein the LED units (12) are disposed along substantially the entire length of the sealed lamp envelope (11).

8. Linear LED light source according to any of the preceding claims, wherein the LED units (12) are mounted to support frames (13a, 13b) that are configured to conduct electric power for driving the LED units (12).

9. Linear LED light source according to any of the preceding claims, wherein the LED units (12) are connected in parallel between the metallic support frames (13a, 13b).

10. Linear LED light source according to any of the preceding claims,

comprising buffer springs (16) that are configured to support the support frames (13a, 13b) against the inner wall of the sealed lamp envelope (11).

11. Linear LED light source according to any of the preceding claims,

comprising isolating bridges (15) that are provided between the support frames (13a, 13b) and are configured to maintain a fixed relative position between the metallic support frames (13a, 13b).