T 0759/04 11-01-2006

1. The appeal is admissible.

2. Amendments (Article 123(2) EPC)

2.1 At the start of the oral proceedings, the appellant proprietor requested permission to amend the main, 1st and 2nd auxiliary requests by introducing the term "aircraft" so that claim 1 would be directed to "A lamp for an aircraft external warning light".

2.2 The patent application discloses either a lamp for an external warning light (cf page 1, lines 3 and 18 to 19 of the published application) or a lamp for an aircraft navigation light (cf ibid, page 1, lines 4 and 7; page 5, lines 1 and 5; page 9, line 6). However, a lamp for an aircraft external warning light is not explicitly disclosed therein.

2.3 The board considers that at the time of drafting the application the inventor considered the use of the lamp for an external warning light without any restrictions as to where the lamp was mounted. This includes a multitude of possible uses and is not restricted to avionics. On the other hand, the disclosed use in the field of avionics was solely as navigation lights.

2.4 Navigation lights allow determining not only the position of the aircraft, but also, if coloured visible lights are used, to determine whether the aircraft is approaching or receding from the observer. Although navigation lights may be considered warning lights, the converse is not true, ie not all warning lights serve navigation purposes.

2.5 Although the patent application discloses lamps combining visible (VL) and infrared (IR) LEDs, switching between the VL and IR LEDs does not transform the navigation lights into warning lights, contrary to the appellant proprietor's representative arguments during the oral proceedings, since they still serve to determine the position of the aircraft, ie a navigation purpose. This understanding corresponds to the disclosure in the application which states that the "aircrafts navigation lights can be switched from normal to covert simply by reversing the polarity of the voltage supplied to them. Where visible navigation lights only are required,…, the IR LEDs can be omitted from the lamp." (cf ibid, page5, lines 1 to 6). It is therefore clearly stated in the application that the lamps remain navigation lights even if switched to the covert (IR) mode.

2.6 Warning lights merely serve to warn. External warning lights in an aircraft call attention to something to be taken care off (eg during servicing the aircraft while landed). Such lamps are however neither explicitly disclosed in nor are they directly and unambiguously derivable from the application.

2.7 The amendment proposed to be made to claim 1 of the main, 1st and 2nd auxiliary requests is, for these reasons, an undisclosed intermediate generalization which does not comply with Article 123(2) EPC and is therefore not a permissible amendment.

3. The appellant proprietor therefore reverted back to his previous main, 1st and 2nd auxiliary requests. Claim 1 according to these requests is reproduced at point II above.

4. Main request - Inventive step - (Article 56 EPC)

4.1 Document D3 discloses a signalling lamp using LEDs as light source which is applicable, in particular, to traffic lights (cf page 1, 1st paragraph). The LEDs are arranged in a series/parallel array and current limiting resistors 16, 17 are connected in series with them (cf Figure 3 and page 5, lines 31 to 37).

4.2 The appellant proprietor argued that document D3 was not a reasonable starting point for assessing the inventive step of the opposed patent, since the lamp disclosed therein was for a traffic signalling light while the patent discloses an incandescent bulb replacement lamp for an aircraft, ie a completely different use in a very different environment.

However, claim 1 is directed to an external warning light and, as already mentioned, is not restricted to an aircraft's navigation light. Document D3 discloses a traffic signalling light, ie something that, in the board's view, can be regarded as an external warning light falling under the wording of claim 1.

4.3 The appellant proprietor has further disputed that this document discloses that the LEDS are mounted on a carrier which is mounted on the body of the lamp and that the current limiting device is mounted within this body. In document D3 the body of the lamp is formed by the cylindrical housing 22 and the screw cap 26 and the current limiting device and the LEDs are both mounted within this body (cf Fig. 4 and page 6, lines 11 to 24).

4.4 The lamp according to claim 1 differs therefore from the lamp disclosed in document D3 in that the array of LEDs is mounted on the lamp's body and in that an integrated circuit is used as current limiting device.

4.5 The opposed patent however does not disclose any technical effect associated with mounting the LEDs on the body of the lamp and the appellant proprietor has also not argued in this sense. The board considers therefore this difference merely as a design option to which no technical significance is attached.

4.6 The problem of thermal runaway of LEDs was well known in the art before the priority date of the opposed patent. The resistance of LEDs decreases when they warm up and, if not prevented, more current is drawn from a constant voltage source as the resistance falls. This causes further heating up of the LEDs, reducing further their resistance. In the end this thermal runaway destroys the LEDs.

Document D19 discloses the use of an integrated circuit as current limiting device in a lamp of LEDs, preventing this self-destructing thermal runaway. The "series resistor" is replaced by an IC which supplies constant current and voltage. Incidentally, the specific IC disclosed in D19 is also the IC mentioned in the opposed patent (cf D19, column 3, lines 46 to 54 and the opposed patent, column 5, lines 1 to 2).

4.7 The board considers therefore that the lamp of claim 1 does not involve an inventive step within the meaning of Article 56 EPC, since the skilled person would have replaced the series resistor employed in document D3 by the IC disclosed in document D19.

5. 1st and 2nd auxiliary request - "Connected in direct series"

5.1 Claim 1 according to these requests states that the integrated circuit (IC) is connected with the LED array in "direct series" between both terminals of the lamp.

5.2 The expression "connected … in direct series" could be interpreted as meaning directly connected in series, ie, as pointed out by the appellant opponent, that nothing else is connected between them. However, such a connection is not disclosed in the patent application. While the circuit shown in Figure 2 discloses a current limiting element 12 directly connected between the terminals and the LEDs array 70, this element is a resistor and not an IC (cf the patent application, page 4, lines 13 to 17). The circuit shown in Figure 5, on the other hand, discloses an IC 123 as current limiting device. However, this embodiment also comprises two forward voltage regulation resistors 121 and 122 connected between the IC and the LEDs (cf ibid, page 6, lines 11 to 15).

Consequently, with this interpretation of "direct series", claim 1 contravenes Article 123(2) EPC.

5.3 The appellant proprietor advanced another interpretation of this expression during the oral proceedings. In his view, this expression should be interpreted as delimiting the claimed lamp with respect to the lamp disclosed in document D3, in which an LED signalling lamp used with alternating current (AC) is disclosed. To drive the LEDs by direct current (DC) a rectifying diode bridge is connected between the terminals of the lamp. Accordingly, the "direct series" connection should limit the connection of the lamp only to DC.

5.4 The board is however of the view that such a limitation cannot be discerned in the expression "connected in … direct series" nor is this interpretation suggested by the patent specification. It follows therefore that claim 1 is neither clear nor supported by the description as required by Article 84 EPC.

5.5 Already this deficiency in the claims would be sufficient for the 1st and 2nd auxiliary request to be refused, nevertheless, the board will in the following also address the issue of inventive step.

6. 1st and 2nd auxiliary request - Inventive step

6.1 Claim 1 of the 2nd auxiliary request specifies further to the features of claim 1 of the 1st auxiliary request that the LEDs are covered by a common transparent potting material. In the following claim 1 of the 2nd auxiliary request will be addressed. However, this discussion applies with equal force to claim 1 of the 1st auxiliary request.

6.2 The lamp according to claim 1 of the 2nd auxiliary request differs from the lamp disclosed in document D3 essentially by the following features:

(a) the lamp is adapted to be driven by application of DC,

(b) the current limiting device is an IC device,

(c) the IC is connected in direct series to the LEDs,

(d) the LEDs are covered by a common layer of a transparent potting material which contacts the carrier between some of the LEDs,

(e) the LED's carrier comprises a ceramic substrate,

(f) the carrier is mounted on a metal heat sink, and

(g) the body of the lamp is a tubular metal body.

6.3 The board shares the view of the appellant opponent that the lamp disclosed in document D3 is adapted to be driven by DC, ie feature (a). Although this conventional lamp has a rectifying diode bridge 11 at the terminal ends of the circuit, this bridge does not prevent the lamp being driven by DC (cf Fig. 2). In any event it is obvious to the skilled person that a rectifying bridge is not needed when the lamp is driven by DC instead of AC. No inventive step can be involved in removing an obviously unnecessary feature.

6.4 As mentioned already at point 4.6 when discussing claim 1 of the main request, feature (b), ie the use of an IC as current limiting device in a lamp of LEDs, is disclosed in document D19.

6.5 As mentioned in point 5, no specific meaning can be attributed to the expression "connected in direct series". Consequently, feature (c) does not contribute to the assessment of inventive step.

6.6 Document D11 discloses that by using individual LED chips instead of finished, discrete LEDs the light output of a lamp can be increased, as the chips may be packed more closely together. However, the larger amount of heat produced has to be safely removed. To this effect it discloses an LED array lamp comprising a ceramic layer 16 on a metal heat sink 12 on which arrays of individual LED chips 14 are mounted. The metal heat sink 36 is connected to the body of the lamp 28 (cf Abstract; column 1, lines 44 to 51; column 1, line 65 to column 2, line 10; column 2, lines 34 to 56; Figures 1 and 5). The array of LEDs is covered with a coating of a transparent epoxy material, ie a transparent potting material, to protect it during handling (cf column 2, lines 26 to 29).

6.7 There is obviously the need specially to protect the LED chips used in D11, as they are much more sensitive to environmental damage than the encapsulated, discrete LED devices used eg in D3. It is moreover implicitly disclosed in this document that the epoxy material contacts the ceramic material between these LED chips. It follows that features (d), (e) and (f) are disclosed in document D11.

6.8 Although document D11 relates to a LED lamp for providing light to enhance and test plant growth and not to an external warning light as the opposed patent does, the skilled person would not, in the view of the board, have ignored its disclosure. Once the skilled person chooses to use LEDs as a high intensity light source he consults the prior art documents relating to this kind of light source that are concerned with increasing the light output. Document D11 addresses in particular how to achieve sufficient light output from a small radiant area. This issue has obvious relevance to the design of a warning light.

6.9 Feature (g), ie that the body of the lamp is a tubular metal body, is a must in a retrofitting lamp which has to have the same overall shape of the incandescent lamp which it is intended to replace. This is for example the case with the lamp disclosed in document D3 in which the lower caps 7 or 8 have different shapes depending on the sockets they have to fit in (cf Fig. 2).

6.10 The lamp of claim 1 addresses therefore the problem of providing in a retrofitting lamp a higher light output while preventing its thermal destruction. This is achieved by improving the current limiting device, ie replacing the passive resistor of document D3 by the integrated circuit disclosed in document D19, and by a higher packing density of the LEDs and removal of the generated heat by the means disclosed in document D11.

6.11 The appellant proprietor has argued that the lamp of claim 1 allows the removal of the heat produced by the LEDs through the metal heat sink to the body of the lamp and from there to the aircraft. The board is not persuaded by this argument, since claim 1 specifies that the ceramic carrier is connected to the body of the lamp without giving any details of the intended type of connection. A mechanical connection between the LED carrier and the body which merely holds the carrier in place, but does not provide any thermal path for removing the heat is also covered by the claim and disclosed eg in document D3.

6.12 For the reasons set out above, the lamp according to claim 1 does not involve an inventive step within the meaning of Article 56 EPC.

7. 3rd auxiliary request

7.1 Towards the end of the oral proceedings before the board, the appellant proprietor submitted a 3rd auxiliary request which was identical to the 2nd auxiliary request except that claim 1 and the claims depending on it had been deleted from it.

7.2 It is the established jurisprudence of the Boards of Appeal that belated amendments to the claims should be admitted during appeal oral proceedings only if the amended claims are clearly allowable (cf eg T 270/90, OJ 1993, 725).

7.3 Independent claim 8 of this request is directed to a lamp for an external warning light comprising inter alia visible and infrared LEDs. A current limiting device is "connected in direct series" between the terminals of the lamp and the array of LEDs. As mentioned in point 5 above the use of this expression in the claims is not permissible either under Article 123(2) EPC or Article 84 EPC. Consequently, the board decided not to admit this request as the claims would not be allowable as they stand.