SMOKE DETECTION UNIT WITH LED DIODE AND PHOTORECEIVER, AND WITH AN LED CHIP AND PHOTOSENSOR ARRANGED IN THE LED DIODE FOR DETERMINING A DEGREE OF AGING AND / OR A LIGHT FLOW COMPENSATION VALUE, AS WELL AS AN LED DIODE

Description

[0001] The invention relates to an optical smoke detection unit for a hazard detector, in particular for a smoke detector. The smoke detection unit comprises at least one light-emitting diode (LED) for emitting light. The LED is a housing made of a transparent, preferably clear, material, containing an LED chip and connecting contacts extending from the housing to contact the LED chip. The smoke detection unit also includes a photodetector for smoke detection, such as a photodiode, which is at least spectrally sensitive to emitted light, and a control unit connected to the LED and the photodetector. The control unit is typically a microcontroller. It is designed at least for electrically controlling the LED (to illuminate) and for evaluating a sensor signal output by the photodetector with regard to fire characteristics.The optical smoke detection unit further comprises a photosensor that is spectrally sensitive to the emitted light. The control unit is also designed to simultaneously acquire an electrical parameter of the photosensor during the electrical control of the LED, in order to derive and output aging information for the LED and / or to determine a decrease in the luminous flux of the LED and correct this by modifying the electrical control of the LED.

[0002] The respective processing steps for the timing control of the two LED chips, as well as the synchronized acquisition and evaluation of the respective photosensor signal, can be implemented by suitable program steps executable on the microcontroller. The LED, the photoreceiver, and the microcontroller are preferably arranged on a circuit board and interconnected.

[0003] Such smoke detection units are generally known. As in the present invention, they can be part of a smoke detector with either a closed or open design. In a closed design, such a smoke detector with a scattered light has an optical measuring chamber that is permeable to smoke to be detected but shielded against direct ambient light. Such a measuring chamber is often also referred to as a labyrinth. Smoke detectors with a scattered light, on the other hand, have a detection chamber located outside the detector housing in the open air. Finally, such smoke detection units can be part of an extinction smoke detector, in which the attenuation of light by the presence of smoke is detected and evaluated by the photoreceiver.

[0004] Published patent application US 2010 / 0328085 A1 discloses a photoelectric smoke detector, in particular an aspirating smoke detector, comprising a source of radiant energy and a closed control loop that responds to a feedback signal of the radiant energy to adjust an output characteristic of the emitted radiant energy and that evaluates a quality characteristic of the emitted radiant energy. The feedback loop and the source can be activated intermittently. The emitted radiant energy is directed onto a lens. The feedback signal is proportional to the radiant energy reflected or scattered by the lens.

[0005] It is also known that LEDs age during operation and exhibit reduced luminous efficacy over time. In contrast, photosensors, such as photodiodes, show comparatively small, negligible signs of aging. Therefore, the luminous efficacy must be monitored to issue a warning message if it is too low for smoke detection. Alternatively, the drive power or pulse duration for the LED can be increased to correct the reduced luminous efficacy or emitted luminous flux. For this purpose, a separate photosensor is known, which preferably receives direct light from the LED and is positioned opposite it. Depending on the photoreceiver signal, the warning message is then issued and / or the luminous efficacy is compensated via the electrical drive of the LED.

[0006] Furthermore, it is known that all optoelectronic components in the smoke detection unit become contaminated over time. This means that the optical transmission power of the LED and the optical detection sensitivity of the photoreceiver for smoke detection, as well as the separate photoreceiver for monitoring light intensity or luminous flux, decrease with increasing contamination, regardless of the aging of these optoelectronic components.

[0007] Finally, light-emitting diodes, in particular single-, two- or multi-color light-emitting diodes, are known from the prior art and are single-piece units. Such light-emitting diodes have an LED housing, at least one LED chip arranged therein for the respective "color", and connecting contacts extending from the LED housing to contact the respective LED chip.

[0008] Based on this, it is an object of the invention to provide an optical smoke detection unit that operates more reliably over the service and operating time.

[0009] The problem is solved by the features of the main claim. Advantageous embodiments of the present invention are specified in the dependent claims. Claims 8 to 10 specify a closed, an open, and an extinction smoke detector, each comprising a smoke detection unit according to the invention.

[0010] According to the invention, the light-emitting diode (LED) has a photosensor that is spectrally sensitive to the emitted light. The photosensor and the LED chip are arranged side by side on a chip carrier of the LED and within the LED housing.

[0011] The control unit is thus configured to preferably detect the photocurrent flowing through the photosensor as a measure of the emitted luminous flux of the controlled LED. It is also configured to derive and output aging information for the controlled LED, dependent on the degree of photocurrent degradation, and / or to adjust the electrical control of the controlled LED accordingly to correct for a corresponding decrease in the emitted luminous flux.

[0012] The photosensor is integrated within the LED housing. Specifically, it is optically coupled to the LED chip(s). As a result, some of the light emitted by the LED chip(s) reaches the photosensor directly or indirectly, for example through scattering or reflection, and can then be detected by it.

[0013] Instead of the photocurrent, a photovoltage generated by the LED can also be measured as an electrical parameter. For this purpose, an ohmic transimpedance resistor is connected in parallel with the LED, which converts the photocurrent flowing through the LED into a photovoltage proportional to it. In this case, the LED, operating as a photodiode, is controlled by the part of the circuit designed for this purpose (see FIG 9 ) activated, which is intended for the electrical control of the light-emitting diode to make it light up.

[0014] The degree of photocurrent degradation can be determined by calculating the difference between a nominal current value for the photocurrent and the current actual value. The nominal current value can be determined, for example, during type or series testing of the optical smoke detection unit. It can also be an average of measured current values ​​taken at the beginning of the smoke detector's operating period. This determined nominal current value can be stored, for example, in the control unit's memory, i.e., in the microcontroller's non-volatile memory. The control unit can be configured to repeatedly, and especially cyclically, acquire a current actual value of the photocurrent and calculate the difference between the stored nominal current value and the currently acquired value. This difference between the two current values ​​then corresponds to the degree of photocurrent degradation.

[0015] The aging information can be, for example, a multi-stage aging grade or a binary aging indicator such as "not aged" or "aged." The aging grade can be represented, for example, by a numerical value or a percentage, such as from 0% to 100%. For instance, a percentage of 0 could represent the new condition, and a percentage of 100 could represent a condition where reliable smoke detection is no longer possible due to insufficient scattered light. The percentage values ​​for the new condition as well as for the state where reliable smoke detection is no longer possible can be determined metrologically, for example, during type testing of the smoke detection unit or smoke detector. Intermediate percentage values ​​can be linearly interpolated. At a predefined value, such as 50% or 80%, a corresponding warning message can then be issued, for example, via a connected detector bus of the smoke detector, wirelessly, and / or audibly or visually on the smoke detector itself.The assignment between the detected photocurrent of the photosensor to the exemplary percentage range of 0% to 100% can be done using a table of numbers or a characteristic curve, which are stored in an electronic memory of the microcontroller for later aging assessment by the microcontroller.

[0016] The control unit can be configured to adjust the emitted luminous flux of the LED (the LED being driven to illuminate) to a required nominal luminous flux for smoke detection using an open or closed control loop. The luminous flux can be changed, for example, by lengthening the pulse duration of the LED's electrical drive, thus increasing the light energy per pulse. Alternatively or additionally, the drive current, and therefore the luminous flux or power of the LED, can be increased. In a closed control loop, the current luminous flux can be continuously measured and adjusted by modifying the LED's electrical drive.

[0017] The key advantage lies in the fact that the LED chip and the photosensor, integrated into a single LED housing, are protected from contamination. This direct optical coupling between the LED chip and the photosensor prevents any particles from entering the optical path. Consequently, the photoreceiver continuously measures the current luminous flux or light output of the LED chip throughout the smoke detection unit's operating time. A certain amount of stray light from the LED chip, whether directly or via reflections from the LED housing, is sufficient for measurement and evaluation.

[0018] By integrating the photosensor into the single-piece LED, an external photosensor is no longer required. The sensor signal output by the photosensor can be measured, for example, via an additional connection point brought out from the LED housing. The photosensor can also have an integrated measuring circuit and be configured to modulate the LED chip's supply current with a current signal corresponding to the currently measured luminous flux value. This signal can then be acquired and evaluated by a measuring circuit outside the LED. In this case, an additional connection point is not necessary.

[0019] In one embodiment, the photosensor is a photodiode, in particular a PIN photodiode, that is spectrally sensitive to the light emitted by the LED chip. The photodiode can also include an integrated electronic measuring amplifier circuit.

[0020] According to one embodiment, the light-emitting diode has two preferably identical LED chips, such as blue or infrared LED chips. Only one of the two LED chips is designed to emit monochromatic light, while only the other, the second LED chip, is designed to function as a photosensor. The control unit is configured to electrically drive only the first LED chip (to illuminate) and simultaneously detect the photocurrent flowing through the second LED chip or a photovoltage generated by the second LED chip in order to derive and output the aging information of the first LED chip. Alternatively or additionally, the control unit can be configured to determine the decrease in the luminous flux of the first LED chip and correct it by adjusting the electrical drive of the first LED chip.

[0021] The invention is based on the understanding that every light-emitting diode can also be used or operated as a photodiode, albeit with a significantly lower efficiency compared to photodiodes specifically designed for detection purposes. Nevertheless, the reflected light received by the other LED chip is usually sufficient to determine, at least qualitatively, the luminous flux of the electrically controlled LED chip.

[0022] The advantage of this embodiment lies in the simple realization of a monitored single-color LED, by applying two identical LED chips side by side on a common LED chip carrier during manufacturing and then contacting them with the connection contacts.

[0023] The LED chips are preferably designed as surface emitters. "Surface emitter" here means that the light is emitted from a flat surface with a Lambertian light distribution. These surface emitters can therefore also be called Lambertian emitters.

[0024] In this case, the control unit is configured to electrically drive one of the LED chips (to illuminate) and switch the other LED chip to operating mode as a photodiode. This can also be done alternately for both LED chips. The control unit is also configured to detect the photocurrent flowing through the other LED chip or the photovoltage generated by the other LED chip as an electrical parameter in order to derive and output the aging information of the respective driven LED chip. Alternatively or additionally, the control unit can be configured to determine the decrease in the luminous flux of the respective driven LED chip and correct it by adjusting the electrical drive of that chip.

[0025] The LED chips typically originate from a wafer containing numerous LED chips manufactured using an optoelectronic semiconductor process. Such a wafer is separated into these numerous LED chips through mechanical processes, particularly sawing or breaking. This "naked" and fully functional component is also referred to as an "ie" (indicating LED). It therefore typically has a square or rectangular shape. A small, but barely usable, portion of the light emitted is also emitted from the lateral edges of such an LED chip. This very portion can be advantageously used for aging monitoring.

[0026] In an advantageous embodiment, the light-emitting diode (LED) is a bicolor LED. As described above, it again comprises a first and a second LED chip for emitting light in a first wavelength range and a second wavelength range different from the first. The photosensor is a photodiode, in particular a PIN photodiode, that is spectrally sensitive to the emitted light. The control unit is configured to selectively electrically drive one of the LED chips (to illuminate) and simultaneously to detect the photocurrent flowing through the photodiode or a photovoltage generated by the photodiode as an electrical parameter in order to derive and output the aging information of the respective driven LED chip.Alternatively or additionally, the control unit is designed to determine the decrease in the luminous flux of the respective controlled LED chip and to correct this by changing the electrical control of the respective controlled LED chip.

[0027] By using a photodiode that is spectrally sensitive to the emitted light of the two LED chips, it is advantageously possible to determine the degree of aging of the two LED chips very accurately and to correct or compensate for it.

[0028] Another advantage lies in the compact integration of the photodiode on the chip carrier together with the two adjacent LED chips. The absence of any possibility of contamination allows for precise determination of the aging of both LED chips.

[0029] The object of the invention is further achieved by a scattered light smoke detector comprising a detector housing and an optical measuring chamber contained therein, with at least one opening for the possible passage of smoke to be detected. A smoke detection unit according to the invention, shielded from ambient light, is housed in the measuring chamber. The photoreceiver is arranged with at least one light-emitting diode in a forward and / or backward scattered light arrangement. The control unit is configured to issue a fire alarm if the sensor signal output by the photoreceiver exceeds a minimum scattered light level. In a forward scattered light arrangement, the angle between the light-emitting diode and the photoreceiver is in the range of 20° to 90°, particularly in the range of 30° to 70°. In a backward scattered light arrangement, this angle is in the range of more than 90° to 160°, particularly in the range of 110° to 150°.

[0030] Furthermore, the problem is solved by an open scattered light smoke detector with a smoke detection unit according to the invention. The latter is arranged in or on a detector housing of the open scattered light smoke detector, with a detection chamber provided for the detection of scattered light then being located outside the detector housing. In other words, no further parts of the detector housing are located between the LED and the detection chamber located outside, on the one hand, and between the photoreceiver and the detection chamber located outside, on the other. Apart from this, a transparent cover may be provided on the detector housing to protect the LED and the photoreceiver from contamination. The control unit is configured to issue a fire alarm if the sensor signal output by the photoreceiver exceeds a minimum scattered light level.

[0031] The object of the invention is further achieved by an extinction smoke detector comprising a detector housing with at least one opening for the possible passage of smoke to be detected, and a smoke detection unit according to the invention arranged in the detector housing and shielded from ambient light. The photoreceiver is arranged opposite the light-emitting diode for the detection of direct light. The control unit is configured to issue a fire alarm if the sensor signal output by the photoreceiver falls below a reference value for a maximum permissible light attenuation.

[0032] The invention and advantageous embodiments of the present invention are explained with reference to the following figures. These show: FIG 1 an exemplary light-emitting diode for a smoke detection unit according to the invention, comprising a first LED chip and a second LED chip or a photodiode for detecting a portion of the light emitted by the second LED chip; FIG 2 a first embodiment with a single LED chip and a photodiode; FIG 3 a second embodiment with two LED chips; FIG 4 the inventive alternating control of two LED chips and metrological evaluation in symbolic representation; FIG 5 a further embodiment with two adjacent LED chips for the emission and detection of edge light emitted by each; FIG 6 a further embodiment with two LED chips and a photodiode for detecting a portion of the light emitted by each LED chip according to the invention; FIG 7FIG. 8 shows an example of light propagation and reflection in an LED housing of exemplary blue and red light and its detection by the respective other LED chip; FIG. 9 shows an exemplary circuit arrangement for the alternating control and evaluation of two LED chips, each by means of a transimpedance converter according to the invention; and FIG. 10 shows an example of a smoke detection unit according to the invention for a scattered light smoke detector with a bicolor LED and with a photoreceiver in a forward scattered light arrangement.

[0033] FIG 1 Figure 1 shows an exemplary light-emitting diode L for a smoke detection unit according to the invention, comprising a first LED chip R, B and a second LED chip B, R, or alternatively, a photodiode PD for detecting a portion of the light emitted by the second LED chip B, R. The reference numeral R indicates that the LED chip preferably emits red or infrared light, while the reference numeral B indicates that it preferably emits blue light. The term OK denotes optical coupling. This symbolically represents the fact that a portion of the light emitted by each LED chip R, B reaches the other LED chip B, R or the photodiode PD in order to be detected there. The reference numeral denotes the terminal contacts of the light-emitting diode L.The light-emitting diode L shown has a transparent LED housing which forms an optical lens LI on the light-emitting side for focusing the emitted light. A denotes the optical axis or principal axis of the light-emitting diode L, along which the emitted light primarily propagates.

[0034] FIG 2 A first embodiment is shown with a single LED chip R, B and with a photodiode PD along the in FIG 1 View direction II shown. Reference numeral 7 denotes an LED housing made of transparent plastic, 8 a chip carrier, and 9 bond wires that contact the LED chip R, B with the connection contacts 1 leading from the LED housing 7 via corresponding contact surfaces 10, 11, 12. 10 designates a common connection contact surface for a common voltage potential and forms a common connection contact 1 externally.

[0035] FIG 3 A second embodiment with two LED chips R, B along the in FIG 1 View direction shown III. According to the invention, the two LED chips R, B are identical optoelectronic components, typically originating from the same batch. By design, the first of the two LED chips R, B is intended for emitting monochromatic light, while the second LED chip R, B is intended for operation as a photodiode. For this purpose, a control unit connected to the two LED chips R, B is configured to electrically control (only) the first LED chip R, B and simultaneously detect the photocurrent flowing through the second LED chip R, B or a photovoltage generated by the second LED chip R, B in order to derive and output the aging information of the first LED chip R, B.Alternatively or additionally, the control unit is configured to determine the decrease in the luminous flux of the first LED chip R, B and to correct this by modifying the electrical control of the first LED chip R, B. A suitable circuit arrangement for this purpose is shown in the example of the... FIG 9 shown.

[0036] FIG 4 The figure shows the inventive alternating control of two LED chips R and B of the light-emitting diode, as well as the measurement-related evaluation, in a symbolic representation. In the left part of the figure, the "blue" LED chip B, symbolized by a closed switch SB, is electrically controlled to emit blue light, while the "red" LED chip R, symbolized by an open switch SR and by a measuring device for recording an electrical parameter of the "red" LED chip R, is switched to photodiode operation and detects a portion of the blue light through optical coupling OK. In the right part of the figure, the "red" LED chip R is now electrically controlled to emit red light, while the "blue" LED chip B is switched to photodiode operation and detects a portion of the red light through optical coupling OK.The detection of blue light by the "red" LED chip R is more efficient than the detection of red light by the blue LED chip B. This is shown in the . FIG 4 symbolized by the smaller pointer deflection at the blue LED chip B compared to the pointer deflection at the red LED chip R.

[0037] FIG 5 Figure 1 shows another embodiment with two adjacent LED chips R, B for the emission and detection of the emitted edge light KL. As shown in Figure 2, FIG 5 As shown, the edges of the two LED chips R and B are positioned opposite each other, allowing the emitted edge light KL to couple directly laterally to the opposite LED chip R and B. In the illustrated embodiment, the "blue" LED chip B has a larger optically active surface area than the "red" LED chip R, by a factor of more than 2.5. "Optically active" refers to the parts of the LED chip's surface that emit light when current is applied. Areas on the surface used for contacting the LED chips, such as those used for bonding a wire, are therefore not included. The larger optically active surface area of ​​the "blue" LED chip B at least partially compensates for the lower electro-optical efficiency in light generation.

[0038] FIG 6 Figure 1 shows a further embodiment with two LED chips R and B and a photodiode PD for detecting a portion of the light emitted by each LED chip R and B according to the invention. The LED is thus a bicolor LED L. The photodiode PD is spectrally sensitive to the emitted bicolor light. The photodiode PD is a PIN photodiode, such as a silicon PIN photodiode, and preferably a silicon PIN photodiode with improved blue sensitivity. Both LED chips R and B and the photodiode PD, which is designed as a chip or is a die, are arranged side by side on the chip carrier 8.

[0039] The Figuren 7 und 8 Figure 7 shows an example of light propagation and reflection in an LED housing 7 of exemplary red and blue light RO, BL, and its detection by the respective other LED chip R, B according to the invention. FIG 7 The "red" LED chip R is controlled to emit red light. The emitted red light rays RO are focused by the optical lens LI formed in the LED housing 7. However, some of the light rays RO are reflected at the interface GF with the surrounding air and, as scattered light, also reach the "blue" LED chip B. Through this optical coupling, light from the "red" LED chip R can be detected by the "blue" LED chip B. FIG 8 Analogously shows the case of emitting blue light and detecting a portion of the reflected blue light rays BL by the "red" LED chip R.

[0040] FIG 9 Figure 1 shows an exemplary circuit arrangement for the alternating control and evaluation of two LED chips R and B, each using a transimpedance converter RTI according to the invention. In the lower part of the FIG 9 The diagram shows a control unit MC implemented as a microcontroller, programmed to alternately open and close the two switches SR and SB. These switches are typically switching transistors. In this example, they are already integrated into the microcontroller MC. The two switches SR and SB alternately connect the two LED chips R and B to a supply voltage VCC for light emission. A resistor RTI, connected in parallel to each LED chip R and B, converts the generated photocurrent IB and IR, respectively, into a corresponding photovoltage UB and UR in "photodiode" mode. The resistance of the two resistors RTI is many times greater than the forward resistance of the LED chips R and B. The resulting photovoltages UB and UR can then be easily acquired by an analog-to-digital converter and evaluated by the microcontroller MC.The A / D converters can also be integrated into the microcontroller (MC).

[0041] FIG 10Finally, an example of a smoke detection unit according to the invention for a scattered light smoke detector is shown. The detector has a two-color light-emitting diode DL and a photoreceiver 2 with a lens 4 in a forward-scattering arrangement. LY denotes an optical measuring chamber that is transparent to the smoke to be detected and shielded from direct ambient light. This is achieved by a suitable arrangement of louvers 6 in the measuring chamber LY. A denotes the optical axis of the light-emitting diode DL and EA the optical receiving axis of the photoreceiver 2. Both axes A and EA form, by way of example, a forward scattering angle of approximately 60°. Z denotes a scattering center. A portion of the scattered light from particles to be detected, which are illuminated by the light-emitting diode DL in this scattering area or scattering volume Z, ultimately reaches the photoreceiver 2.To prevent direct light from the LED DL from reaching the photoreceiver 2, additional apertures 3 and 5 are provided. RO' and BL' denote emitted light beams that pass through aperture 3 of the LED DL. According to the invention, a backscattering object OB or a reflective layer F can be placed between the LED DL and aperture 3, so that part of the emitted light beam RO, BL is reflected back towards the LED DL. A portion of this scattered light S then reaches the respective, uncontrolled LED chip R, B. A photovoltage generated at this LED chip R, B can then be detected and evaluated via the connection contacts 1 of the LED DL. Reference symbol list

[0042] 1, 10-13 Connection contacts 2 Photosensor, photodiode, silicon pin photodiode 3 Aperture, aperture 4 Photoreceiver lens 5 Photoreceiver aperture 6 Blade, light-shielding element 7 Housing, LED housing, LED housing 8 LED chip carrier, carrier, carrier plate 9 Bonding wires Aoptical axis, optical transmitting axis B Blue LED chip BL Blue light beam BL' Passing blue light beam DL Dual-color LED, dual-LED E Optical axis, optical receiving axis Reflective layer, color layer GF Optical interface IR, TB Photocurrent KLK Edge light L Light-emitting diode, LED LI Optical lens LY Optical measuring chamber, labyrinth MC Control unit, microcontroller OB Backscattering object OK Optical coupling PD Photosensor chip, photodiode R Red LED chip RO Red light beam RO' Passing red light beam R TI Resistor, transimpedance converter S Backscattered light SR, SB Controllable switch, transistor UR, UB Photovoltage VCC Supply voltage Z Scattered light center, measuring volume

Claims

1. Optical smoke detection unit for a danger detector, in particular for a smoke detector, which comprises at least - one light-emitting diode (L) for emitting light, wherein the light-emitting diode (L) comprises an LED housing (7) produced from a transparent material, preferably from a clear material, with an LED chip (R, B) arranged therein and terminal contacts (1) in contact with the LED chip (R, B) and leading out of the LED housing (7), - a photoreceiver (2) which is at least spectrally sensitive to emitted light for the smoke detection, - a control unit (MC) which is connected to the light-emitting diode (L) and to the photoreceiver (2) for the electrical activation of the light-emitting diode and for evaluating a sensor signal emitted by the photoreceiver (2) relative to fire parameters, - a photosensor (PD) which is spectrally sensitive to the emitted light, - wherein, during the electrical activation of the light-emitting diode (L), the control unit (MC) is designed at the same time to detect an electrical parameter of the photosensor (PD), in order to derive therefrom and to emit ageing information of the light-emitting diode (L) and / or in order to determine therefrom a reduction of the light flux of the light-emitting diode (L) and to correct this by changing the electrical activation of the light-emitting diode (L), characterised in that - the light-emitting diode (L) is an integral structural unit and comprises the photosensor (PD) which is spectrally sensitive to the emitted light, and - the photosensor (PD) and the LED chip (R, B) are arranged adjacent to one another on a chip support (8) of the light-emitting diode (L) and in the LED housing (7).

2. Smoke detection unit according to claim 1, wherein the photosensor (PD) is a photodiode which is spectrally sensitive to the emitted light, in particular a PIN photodiode.

3. Smoke detection unit according to claim 1, wherein the light-emitting diode (L) has two LED chips (R, B), preferably of the same type, wherein a first of the two LED chips (R, B) is provided for emitting a single-color light, while the other second LED chip (R, B) is provided for operating as a photodiode (PD), wherein the control unit (MC) is designed to activate the first LED chip (R, B) electrically and at the same time to detect the photocurrent (IR, IB) flowing through the second LED chip (R, B) or a photovoltage (UR, UB) produced by the second LED chip (R, B), in order to derive therefrom and to emit ageing information of the first LED chip (R, B) and / or to determine therefrom the reduction of the light flux of the first LED chip (R, B) and to correct this by changing the electrical activation of the first LED chip (R, B).

4. Smoke detection unit according to claim 3, wherein the two LED chips (R, B) are arranged adjacent to one another on a chip support (8) of the light-emitting diode (D, DL), wherein one edge of an LED chip (R, B) opposes an edge of the other LED chip (B, R) so that edge light (KL) of one LED chip (R, B) emitted at the side is optically coupled into the other LED chip (B, R) at the side.

5. Smoke detection unit according to claim 1, wherein the light-emitting diode (L) is a two-colour light-emitting diode (DL), wherein the two-colour light-emitting diode (DL) has a first and a second LED chip (R, B) for emitting light in a first and in a second wavelength range which is different therefrom, wherein the photosensor (PD) is a photodiode which is spectrally sensitive to the emitted light, in particular a PIN photodiode, and wherein the control unit (MC) is designed to activate optionally one of the LED chips (R, B) electrically and at the same time to detect the photocurrent (IR, IB) flowing through the photodiode (PD) or a photovoltage (UR, UB) produced on the photodiode (PD) as an electrical parameter, in order to derive therefrom and to emit the ageing information of the respectively activated LED chip (R, B) and / or in order to determine therefrom the reduction of the light flux of the respectively activated LED chip (R, B) and to correct this by changing the electrical activation of the respectively activated LED chip (R, B).

6. Smoke detection unit according to one of the preceding claims, wherein at least one of the LED chips (R, B) is configured for emitting light in a wavelength range of 665 nm to 1000 nm and / or for emitting light in a wavelength range of 350 nm to 500 nm.

7. Smoke detection unit according to one of the preceding claims, wherein the light-emitting diode (D, DL) has a standard plastics housing with a 3 mm or 5 mm diameter or wherein the light-emitting diode (D, DL) is an SMD component for surface-mounting on a circuit support.

8. Scattered light smoke detector which comprises a detector housing and an optical measuring chamber (LY) received therein with at least one opening for the possible passage of smoke to be detected, wherein a smoke detection unit, according to one of the preceding claims 1 to 7, which is shielded against ambient light is received in the measuring chamber (LY), wherein the photoreceiver (2) is arranged with at least one light-emitting diode (L, DL) in a forward-scattered and / or back-scattered light arrangement and wherein the control unit (MC) is designed to emit a fire alarm if the sensor signal emitted by the photoreceiver (2) exceeds a minimum scattered light level.

9. Open scattered light smoke detector, comprising a smoke detection unit according to one of the preceding claims 1 to 7, wherein the smoke detection unit is arranged in a detector housing of the open scattered light smoke detector, wherein a detection chamber provided for the detection of scattered light is located outside the detector housing and wherein the control unit (MC) is designed to emit a fire alarm if the sensor signal emitted by the photoreceiver (2) exceeds a minimum scattered light level.

10. Light extinction smoke detector comprising a detector housing with at least one opening for the possible passage of smoke to be detected and a smoke detection unit, which is arranged in the detector housing and shielded relative to ambient light, according to one of the preceding claims 1 to 7, wherein the photoreceiver (2) is arranged opposite the light-emitting diode (L, DL) for detecting direct light and wherein the control unit (MC) is designed to emit a fire alarm if the sensor signal emitted by the photoreceiver (2) falls below a comparison value for a maximum permitted light attenuation.