CN120344835A - Spectral light sensor and corresponding sensing method - Google Patents

Abstract

The object of the invention is to provide a cost-effective and simple light sensor (2) with red, green and blue optical channels, the light sensor (2) having high sensing accuracy and stability under varying angles of incidence, in particular for illuminance and color temperature measurements. To this end, the invention proposes a light sensor (2) with a red channel comprising at least one main red photodiode (20) with a first filter stack comprising a UV-IR blocking interference filter (8) and a red absorption filter (24) and at least one supplementary photodiode (22) with a second filter stack comprising an interference bandpass filter (26) and an absorption filter, both the main red photodiode (20) and the supplementary photodiode (22) being fed into a common analog ALS engine (30) or an evaluation unit configured to add their respective responses to form a red channel output (34), such that the response of the supplementary photodiode (22) at least partially compensates for a loss of the response of the main red photodiode (20) with respect to a varying angle of incidence of incident light.

Description

Spectroscopic sensor and corresponding sensing method

Technical Field

The present invention relates to a spectral light sensor having a red optical channel, a green optical channel and a blue optical channel. The invention also relates to a corresponding sensing method.

Background

Existing light sensors having red, green, blue (RGB) and (if applicable) transparent optical channels are susceptible to sensing inaccuracies due to angular offset (i.e., when the angle of incident light with respect to the optical axis varies over time or with respect to a calibration or reference alignment).

Disclosure of Invention

It is an object of the present invention to provide a cost-effective and simple light sensor with RGB optical channels, which has high sensing accuracy and stability at varying angles of incidence, in particular for illuminance and color temperature measurements. A corresponding sensing method will also be presented.

With respect to the light sensor, the object is achieved by a light sensor according to claim 1. The corresponding method is specified in claim 8.

Thus, there is a light sensor having a red optical channel, a green optical channel, and a blue optical channel, the red channel comprising at least one primary red photodiode having a first filter stack comprising a UV-IR blocking interference filter and a red absorption filter, and at least one supplemental photodiode having a second filter stack comprising an interference bandpass filter and an absorption filter, both the primary red photodiode and the supplemental photodiode feeding into a common analog ALS engine or a common evaluation unit configured to add their respective responses to form a red channel output, such that the supplemental photodiode response at least partially compensates for a loss of the primary red photodiode response to a varying angle of incidence (A VARYING ANGLE of incodence) of incident light.

Briefly, a light sensor according to the present invention has at least two pixels with different combinations of filters (and thus different spectral responses) fed into the same red channel output. The supplemental photodiode increases the response to the red channel, which compensates for the loss of response versus angle due to the shift in the cut-off wavelength of the interference filter.

In other words, the filter stack (including the absorption filter and the interference filter) on the supplemental photodiode uses a unique interference filter that is preferably spectrally shifted at the same rate as the UV-IR blocking filter used on the main red channel photodiode. Thus, the filter stack on the supplemental photodiode is designed to increase the response with respect to angle, which matches the loss of response with respect to angle of the filter stack on the main red channel photodiode.

This enables accurate and stable illuminance and color temperature measurements at varying angles of incidence, which is an important improvement especially for applications of display management and camera enhancement that are widely used in mobile devices such as smartphones.

In addition to the problem of angular offset that has been addressed and the stable color channel ratio that is achieved when changing the angle of incidence, the combined absorption filter stack and interference filter stack provides several other advantages:

● Low cost component

● Low-cost production process

Zero device height increase

Low complexity

Easy system integration

No field of view restriction

No sensitivity loss

In particular, the present invention enables the use of lower cost packages because no package holes are required. Furthermore, the present invention enables a lower cost system design because no diffuser is required.

In a preferred embodiment, the absorption filter of the second filter stack is a green absorption filter. Preferably, the green absorbing filter has a transmittance maximum in the range of 500nm to 550nm, preferably with a falling edge in the visible light region.

In general, there are other available absorbing filters such as CMY (cyan, magenta, yellow), where cyan and magenta may be used. However, for RGB sensors, green is the most cost-effective.

Furthermore, it is preferable that the interference bandpass filter has a passband at a lower wavelength limit in the range of 525nm to 645nm, in particular a lower wavelength limit of 585nm, with respect to normal incidence light. Preferably, the passband has an upper wavelength limit in the range of 600nm to 720nm relative to normal incidence light, in a preferred example an upper wavelength limit of 685 nm.

Advantageously, the spectral shift of the interference bandpass filter response with respect to the angle of incidence matches the spectral shift of the UV-IR blocking interference filter response.

Advantageously, the green and blue channels each comprise a photodiode with a filter stack comprising a UV-IR blocking interference filter and a green or blue absorbing filter.

In a useful application, a device with a light sensor of the above-mentioned type, in particular a mobile phone, a tablet, a portable computer, a wearable device, a television set or the like, is configured for sensing ambient light and/or for determining a relevant color temperature and/or for camera image processing. The invention enables better display (color) quality, better picture (color) quality and/or better Correlated Color Temperature (CCT) sensing accuracy.

A corresponding method of spectral sensing of light, preferably ambient light, is based on a light sensor having a red optical channel, a green optical channel and a blue optical channel, the red channel comprising at least one primary red photodiode having a first filter stack comprising a UV-IR blocking interference filter and a red absorption filter and at least one complementary photodiode having a second filter stack comprising an interference bandpass filter and an absorption filter, wherein the primary red photodiode response and the complementary photodiode are combined, in particular added, to form a red channel output such that the complementary photodiode response at least partially compensates for a loss of the primary red photodiode response with respect to a varying angle of incidence of the incident light.

The content described in relation to the device can be similarly applied to the method and therefore need not be repeated here. Method embodiments and details have counterparts in the apparatus and vice versa.

Drawings

Advantageous embodiments of the present invention will now be discussed with reference to the accompanying drawings.

Fig. 1 shows a schematic cross-sectional view of a conventional light sensor with RGBC (red-green-blue-transparent) optical channels.

Fig. 2 shows a graph of transmittance at a fixed angle of incidence in relation to various filter responses (i.e., RGB and UV-IR filter transmission curves) of the different components of the light sensor of fig. 1.

Fig. 3 shows a response plot relating to various filter transmissivities (i.e., normalized RGB output) of the overall photosensor of fig. 1 at a fixed angle of incidence.

Fig. 4 shows the angular dependence or offset of the UV-IR filter response of the light sensor of fig. 1.

Fig. 5 shows the angular dependence or offset of the red and blue channel responses of the light sensor of fig. 1.

Fig. 6 shows a light sensor with an upstream diffuser.

Fig. 7 shows a light sensor with an upstream optical aperture.

Fig. 8 shows a photodiode with an exemplary filter stack, which is used as a complementary photodiode in combination with the light sensor according to fig. 1.

Fig. 9 schematically shows an improved red channel measurement device for a light sensor using a complementary photodiode according to fig. 8.

Fig. 10 shows various spectral responses for different angles of incidence in relation to the complementary photodiode according to fig. 8 and its respective filter components.

Fig. 11 shows the spectral red channel response of a modified light sensor with a main red photodiode and a complementary photodiode according to fig. 8 for different angles of incidence.

Fig. 12 shows the spectral blue channel response and the spectral red channel response for different angles of incidence of a modified light sensor with a main red photodiode and a complementary photodiode according to fig. 8.

Fig. 13 shows the ratio of blue channel response to red channel response (angular response under different types of light sources) versus angle of incidence for a conventional light sensor and a modified light sensor.

Detailed Description

Fig. 1 shows a schematic cross-section of a light sensor 2 with RGBC (red-green-blue-transparent) optical channels, also referred to as RGBC sensor. The light sensor 2 comprises a plurality of optical pixels arranged in an array or matrix configuration in a top view (along an optical path or optical axis 4). Each optical pixel comprises one of a Photodiode (PD) 6, a UV-IR blocking interference filter 8 (in particular a coating), and a color absorbing filter 10 (in particular a coating) or a transparent cover 12 (in particular a coating). More precisely, a first group of pixels is assigned a red absorbing coating, a second group of pixels is assigned a green absorbing coating, a third group of pixels is assigned a blue absorbing coating, and optionally a fourth group of pixels is assigned a (colorless) transparent cover. Alternatively, for transparent pixels, there may be no coating at all over the UV-IR blocking interference filter 8. In terms of layers, at the bottom is a photodiode layer, in the middle is a UV-IR blocking layer, and at the top is an RGBC mask 14. Typically, there is a base layer below the photodiode layer, but not shown here.

Typically, the UV-IR layer may be an intermediate layer or a top layer. Similarly, the RGBC layer may be an intermediate layer or a top layer.

The transparent channel is optional. That is, in a simple RGB photosensor, there are no transparent pixels. The invention is applicable to both RGB and RGBC photosensors.

The UV-IR blocking interference filter or coating may be referred to simply as a UV-IR filter and the RGB absorbing filter or coating may be referred to simply as an RGB filter.

The spectral transmittance, i.e. the transmittance in percent (%), with respect to the wavelength in nm of the incident light, for the various components of the light sensor 2 is shown in fig. 2.

In the graph, the respective transmittance for each of the RGB absorbing filters 10 or coatings is shown. The transmittance curve for the blue absorbing coating has a first prominent maximum at approximately 450nm, the corresponding first maximum for the green absorbing coating at approximately 530nm, and the curve representing the effect of the red absorbing coating has a first maximum at approximately 600 nm. Toward longer wavelengths, all three curves show rising behavior in the Infrared (IR) region, which means that the RGB color coating is substantially transmissive to IR light. To a lesser extent, this is also true for shorter wavelengths in the Ultraviolet (UV) region. The optional transparent coating (if present) is substantially transmissive for the entire range of wavelengths.

Furthermore, the graph in fig. 2 shows a typical transmittance curve for the UV-IR blocking interference filter 8. The filter or coating shows bandpass behavior in terms of transmittance, producing high transmittance in the visible range (approximately from 400nm to 700 nm) and low (almost zero) transmittance below and above the visible range. That is, light having wavelengths in the UV and IR ranges is blocked, while visible light is allowed to pass, thus obtaining the name UV-IR blocking filter. Typically, such filters are designed as interference filters.

The photodiode 6 of each optical channel has its own spectral response behavior (not shown here). The wavelength at which the photodiode 6 has the maximum response depends on the photodiode structure. The example shown here has a maximum at approximately 750nm, where the attenuation is relatively gentle towards lower and higher frequencies.

For each of the optical channels of the light sensor 2, a total spectral response is obtained by combining the response and transmittance of the individual components (i.e. the photodiode 6, the UV-IR blocking interference filter 8 and either the RGB color absorption filter 10 or the transparent cover 12). Mathematically, for each wavelength of interest, the corresponding response values are multiplied by each other, resulting in the result graph in FIG. 3. The resulting spectral response for each of the RGB channels is visualized by three corresponding curves (the combined response of the UV-IR blocking filter 8 and the photodiode 6 is also shown). Specifically, the normalized response in percent (%) is given in terms of wavelength in nm. Although the original position of the transmittance maximum according to the RGB curve of fig. 1 is approximately maintained, the overall effect of the UR-IV blocking filter 8 is clearly visible, since the transmittance in the UV and IR range is almost zero.

In summary, the color sensor typically uses red, green, and blue (RGB) absorbing filters 10. However, the RGB absorbing filter 10 passes light in the IR range and UV range, which is undesirable. Thus, the RGB absorber filter 10 needs to be coupled with the UV-IR blocking interference filter 8 to block the IR and UV portions of the incident light.

The problems associated with the conventional photosensor design of fig. 1 result from the fact that the UV-IR blocking interference filter 8 has a transmittance characteristic that depends on the angle of incidence (AoI) of the incident light. Strictly speaking, the transmittance map of the UV-IR filter and the resulting response map of the RGB channel of the light sensor 2 are valid only for a fixed reference value of AoI =0°, wherein AoI is given with respect to the optical axis 4. For other AoI values, the corresponding response curve is offset from the reference curve.

This angular offset from the UV-IR blocking interference filter 8 can be clearly seen in fig. 4, wherein the spectral response of the UV-IR blocking interference filter 8 (in combination with the photodiode response) is given as normalized response in percent (%) versus wavelength in nm (nm) for five different AoI values ranging from 0 ° to 75 °.

Fig. 5 is a similar graph showing the angular offset and the angle-dependent planarization of the transmittance curves for the red and blue channels of the conventional light sensor 2 of fig. 1. Specifically, the normalized response in percent (%) of the red and blue channels with respect to the wavelength in nm is given for two different AoI values (i.e., 0 ° and 60 °).

The red channel has a similar angular offset as the UV-IR blocking interference filter 8. Blue and green, especially green, are less affected. This can be explained by the fact that each RGB channel is formed in combination with a UV-IR blocking interference filter 8. In other words, the UV-IR blocking interference filter 8 is common to the RGB channels and the transparent channels (if present) and thus affects them in a similar way. In particular, for higher AoI values, the peak height of the response curve is reduced. This height reduction is mainly due to the photodiode 6 reduced effective sensing area at high angles. Furthermore, as the angle increases, there is a left shift (toward lower wavelengths) from the UV-IR blocking interference filter 8. However, since the transmittance peak in the red color range narrows at a high incidence angle, the UV-IR blocking interference filter 8 has the most prominent or significant effect on the red channel. For the green channel (not shown) the effect is less pronounced, and more so for the blue channel. Thus, the ratio of the red channel response to the blue channel response is particularly affected.

This behavior is particularly disadvantageous for sensing applications in which the outputs of the different channels of the light sensor 2 are compared or correlated with each other. In particular, this behavior produces inaccurate results for illuminance (typically measured in Lux) or Correlated Color Temperature (CCT) estimation.

In summary, the upper cut-off frequency of the UV-IR blocking interference filter 8 depends on the angle of incidence of the light. The UV-IR blocking interference filter 8 also sets the cut-off frequency of the response of the red channel, which is therefore also dependent on the angle of incidence. Thus, the larger the angle, the less proportional the decrease in response of the red channel is to the decrease in response of the blue channel. This is especially disadvantageous for CCT performance and similar applications, where ideally the red channel to blue channel response ratio should remain flat (i.e., constant) with respect to angle.

Fig. 6 shows a first possible remedy for the problem. The solution comprises a diffuser 16 placed in the path of the incident light. The light rays emerging from the diffuser 16 are statistically distributed with respect to their direction, irrespective of the angle of incidence of the incident light, so as to create a fixed illumination condition for the light sensor 2 (here exemplarily shown as being arranged on a substrate).

Problems associated with this approach include the high cost of the diffuser 16, the high complexity of the integration of the diffuser 16, and significant sensitivity degradation (high quality diffusers 16 typically have less than 50% transmittance).

Fig. 7 shows a second possible remedy for the problem. The solution comprises an optical aperture 18 placed in the path of the incident light, which aperture limits the field of view (FoV) with respect to the light sensor 2 arranged further down the optical path. In other words, the optical aperture 18 blocks light having a high incidence angle, and allows only light having an incidence angle (AoI ≡0) of almost zero to pass through and reach the photosensor 2. In an example, the optical aperture 18 is a small hole or opening in a light blocking opaque or non-transparent material or other light transmitting or transparent region.

Problems associated with this approach include an increase in device height or system height, a decrease in FoV, and a significant decrease in sensitivity due to the decrease in FoV.

To overcome these problems, a new sensor design is proposed, which is schematically shown in fig. 8 and 9 in connection with fig. 1. The key point is that in addition to the conventional red photodiode (referred to as the main red photodiode 20), the supplemental photodiode 22 increases the response to the red channel to compensate for and aim at matching the blue channel response depending on the change in angle of incidence.

The main red photodiode 20 is constructed as described above. That is, there is a UV-IR blocking interference filter 8 (particularly a coating) disposed on the photodiode 6. On top of this there is a red absorbing filter 24 (in particular a coating). Thus, the main red photodiode 20 has the spectral response described above, which need not be repeated here. The various layers or coatings are preferably stacked upon one another without any gaps therebetween, nor any optically active intermediate layers, although there may be optically irrelevant adhesive layers or the like.

In principle, the order of the UV-IR blocking interference filter 8 and the red absorption filter 24 can be interchanged without affecting the spectral response. In practice, however, it is advantageous to first apply the UV-IR blocking interference filter 8 as a coating on the photodiode 6 and then to apply the red absorption filter 24 on top.

On the other hand, the supplemental photodiode 22 is configured as schematically shown in fig. 8. A dedicated interference Bandpass (BP) filter 26, in particular a coating, is arranged on the photodiode 6. On top of this there is an absorption filter 28, in particular a coating, in particular a green absorption filter.

Here too, the order of the filters in the filter stack can in principle also be interchanged without affecting the spectral response. In practice, however, it is advantageous to first apply the interference bandpass filter 26 as a coating on the photodiode 6 and then to apply the (green) absorption filter 28 on top. Also, the various layers or coatings are preferably stacked upon one another without any gaps therebetween, nor any optically active intermediate layers, although there may be optically irrelevant adhesive layers or the like.

The effect of the filter stack can be understood from the three graphs in fig. 10.

In the uppermost graph, on the one hand, the spectral transmittance of the green absorption filter 28 is indicated for AoI =0° (i.e., normal incidence of light). It is expected that the spectral curve (labeled green only) which is a combination of the green filter spectral transmittance and the photodiode 6 spectral response has a first maximum around 530nm, corresponds to the green spectral region, and has a relatively steep decay or dip to both sides. In the IR region, the green transmittance curve rises again, going forward from approximately 700nm, and has a second slightly wider maximum centered around 850 nm.

On the other hand, the spectral transmittance of the interference bandpass filter 26 is also indicated for AoI =0°. As the name implies, bandpass is a filter that passes wavelengths within a range (referred to as passband) and rejects (or attenuates) wavelengths outside that range. In this particular case, the lower limit or cutoff wavelength of the passband is around 585nm (hence labeled 585 BP), and the upper limit or cutoff wavelength is around 660nm, centered around 630 nm. In other words, the passband for AoI =0° is located at the minimum of the green transmittance curve between the first maximum and the second maximum and is similar in shape and position to the red absorption peak for the main red photodiode according to fig. 3.

In the middle graph, the green transmittance curve and the interference filter passband for AoI =60° are shown. In general, the green transmittance curve is slightly flatter (with less prominent peaks) than the 0 ° corresponding curve, which is mainly caused by the smaller effective incident area on the photodiode due to the oblique incidence angle. The same height reduction occurs over the passband of the interference bandpass filter 26. More importantly, the passband of the interference bandpass filter 26 has been shifted to the left, toward the lower wavelengths, and now overlaps and nearly covers the green absorption peak of the green absorption filter 28.

The combined effect of the filter stack on the supplemental red photodiode 22 is obtained by multiplying the individual contributions (i.e., contributions from the interference bandpass filter 26 and the green absorption filter 28 (and photodiode 6)). The resulting spectral response of the supplemental red photodiode 22, including the effect of the filter stack, is shown in the bottom-most graph of fig. 10 for two different angles of incidence, aoI =0° and AoI =60°. It can be seen that for 0 deg., the response of the supplemental red photodiode 22 is almost zero and therefore negligible. However, for larger angles like 60 °, the response curve is shifted to the left, towards lower wavelengths, and has a non-negligible contribution with peaks in the green range around 550 nm.

As indicated above in connection with fig. 9, both the main red photodiode 20 and the supplemental photodiode 22 feed their respective outputs into a common analog ALS engine 30 (als=ambient light sensor) that produces a combined output from the two signal inputs. For example, the simulated ALS engine 30 may generate a sum value (sum value) or arithmetic average or otherwise weighted sum or combination value based on the added contributions from the respective signals described above. The analog sum signal (analog sum signal) may be fed into an analog-to-digital converter (ADC) 32 to provide a digital red channel output 34.

In a broad variation, the main red photodiode 20 and the supplemental photodiode 22 do not have to be connected to a common analog ALS engine 30. Rather, the supplemental diode 22 may be a separate channel with its own dedicated analog ALS engine and ADC. Thus, software implemented in the evaluation unit or control unit may access the device to obtain results from the main photodiode 20 and the supplemental photodiode 22, and make mathematical compensation in the software. For example, the mathematical compensation may be a simple linear addition by applying different gains to the supplemental channels or a weighted compensation based on, for example, the IR ratio detected in the ambient light, or any customized compensation based on specific characteristics in the actual product (e.g., curve compensation, look-up table, etc.). Additionally or alternatively, the supplemental photodiode 22 may be fed into the deep learning network as a separate input.

In summary, the filter stack on the supplemental photodiode 22 includes a (preferably green) absorbing filter 28 in combination with a dedicated interference bandpass filter 26, which dedicated interference bandpass filter 26 is spectrally shifted with respect to angle at the same or at least similar rate as the UV-IR blocking interference filter 8 used on the primary red photodiode 20. Thus, the filter stack on the supplemental photodiode 22 is designed to increase the response with increasing angle of incidence such that the increased response matches the simultaneous loss of response of the filter stack (red absorption filter 24 and UV-IR blocking interference filter 8) on the primary red photodiode 20 with respect to angle. Thus, the supplemental red photodiode 22 adds a response to the red channel that ideally matches the relative increase in blue channel response with respect to angle.

This is shown in fig. 11 and 12. In fig. 11, the resulting red channel spectral response from the combined main red photodiode 20 and supplemental red photodiode 22 is shown for five different AoI values ranging from 0 ° to 75 °. In fig. 12, the modified or enhanced red channel response is shown together with the conventional blue channel response for two different angles, namely 0 ° and 60 °. Although for 0 °, the two curves are almost the same shape as those of the conventional photosensor in fig. 5, for larger angles (such as 60 °), the peak height loss of the red channel response relative to the blue channel response is less severe than in fig. 5. In an example, even for higher angles, the red channel peak still dominates over the blue channel peak. In other words, the (new) improved red channel response with the supplemental red photodiode 22 shows a smaller variation with respect to angle than a conventional red channel without the supplemental red photodiode 22.

The results are further shown in fig. 13, where each of the four graphs shows the ratio of blue channel response to red channel response with respect to varying angles (from 0 ° to 75 °), first for the regular red channel and second for the new red channel. The upper left graph shows the angular response to sunlight, the upper right graph is obtained from fluorescent lighting, the lower left graph is related to warm white LEDs, and the lower right graph is related to incandescent lamps. In all four cases, the angular response ratio of the improved sensor is substantially flat or constant compared to the original sensor design. This provides various advantages for sensing applications requiring accuracy and angular stability, particularly for illuminance and color temperature measurement applications.

While the present invention provides the advantage that the upstream diffuser 16 or optical aperture 18 is not generally required, each of the upstream diffuser 16 or optical aperture 18 (alone or in combination) may still be present to achieve optimal color stability.

List of reference numerals

Optical sensor 2

Optical axis 4

Photodiode 6

UV-IR blocking interference filter 8

Color absorbing filter 10

Transparent cover 12

RGBC mask 14

Diffuser 16

Optical aperture 18

Main red photodiode 20

Complementary photodiode 22

Red absorbing filter 24

Interference bandpass filter 26

Absorption filter 28

Analog ALS engine 30

Analog-to-digital converter 32

Red channel output 34

Claims (10)

1. A light sensor (2) having a red optical channel, a green optical channel and a blue optical channel, the red channel comprising at least one main red photodiode (20) having a first filter stack comprising a UV-IR blocking interference filter (8) and a red absorption filter (24) and at least one supplementary photodiode (22) having a second filter stack comprising an interference bandpass filter (26) and an absorption filter (28), the main red photodiode (20) and the supplementary photodiode (22) both being fed into a common analog ALS engine (30) or an evaluation unit configured to add their respective responses to form a red channel output (34), such that the response of the supplementary photodiode (22) at least partially compensates for the loss of the response of the main red photodiode (20) with respect to a varying angle of incidence of incident light. 2. The light sensor (2) according to claim 1, wherein the absorption filter (28) of the second filter stack has a falling edge in the visible light region. 3. The light sensor (2) according to claim 1 or 2, wherein the absorption filter (28) of the second filter stack is a green absorption filter. 4. The light sensor (2) according to any one of the preceding claims, wherein the interference bandpass filter (26) has a passband with a lower wavelength limit in the range of 552 nm to 645 nm with respect to normally incident light. 5. The light sensor (2) according to claim 4, wherein the passband has an upper wavelength limit in the range of 600 nm to 720 nm with respect to normally incident light. 6. The light sensor (2) according to any of the preceding claims, wherein the spectral shift of the response of the interference bandpass filter (26) with respect to the angle of incidence matches the spectral shift of the response of the UV-IR blocking interference filter (8). 7. A light sensor (2) according to any of the preceding claims, wherein the green channel and the blue channel each comprise a photodiode (6) having a filter stack comprising a UV-IR blocking interference filter (8) and a green or blue color absorption filter (10). 8. A method for spectral sensing of light by means of a light sensor (2) having a red optical channel, a green optical channel and a blue optical channel, the red channel comprising at least one primary red photodiode (20) having a first filter stack comprising a UV-IR blocking interference filter (8) and a red absorption filter (24) and at least one supplementary photodiode (22) having a second filter stack comprising an interference bandpass filter (26) and an absorption filter (28), wherein the response of the primary red photodiode (20) and the response of the supplementary photodiode (22) are combined, in particular added, to form a red channel output (34) such that the response of the supplementary photodiode (22) at least partially compensates for the loss of the response of the primary red photodiode (20) with respect to a varying angle of incidence of incident light. 9. The method of claim 8, wherein the response of the primary red photodiode (20) and the response of the supplemental photodiode (22) are combined in a common analog ALS engine (30) prior to digitization. 10. The method of claim 8, wherein after digitization, the response of the main red photodiode (20) and the response of the supplementary photodiode (22) are combined by a software routine of an associated evaluation unit.