WO2010125496A1

WO2010125496A1 - Method and apparatus of driving a light source depending of the daylight

Info

Publication number: WO2010125496A1
Application number: PCT/IB2010/051729
Authority: WO
Inventors: Eberhard Waffenschmidt; Dirk Hente
Original assignee: Koninklijke Philips Electronics N. V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2009-04-27
Filing date: 2010-04-20
Publication date: 2010-11-04
Also published as: TW201106791A

Abstract

An apparatus comprises a control unit and a daylight sensing OLED element for providing a daylight sensing signal to the control unit. The control unit performs at least one control step in dependency on the power of daylight sensed by the OLED.

Description

METHOD AND APPARATUS OF DRIVING A LIGHT SOURCE DEPENDING OF THE DAYLIGHT

FIELD OF THE INVENTION

The present invention relates to the field of OLED elements, and more particularly to organic light emitting diode (OLED) devices.

BACKGROUND OF THE INVENTION

OLED elements comprise electroluminescent material that is capable of emitting light when a current is passed through it. The material used for OLED elements can be light emitting polymers or small organic molecules. Organic devices may, for example be organic light emitting diodes (OLEDs), which are known in the art. For activating the OLED elements, current is applied to the electroluminescent material by means of the electrodes disposed at surfaces of the electroluminescent material.

OLED elements, such as OLEDs, comprise electroluminescent material disposed between electrodes. Upon application of a suitable voltage, current flows through the electroluminescent material from anode to cathode. Light is produced by radiative recombination of holes and electrons inside the electroluminescent material.

In US2006/0028156 Al a system and a method for generating light using light-emitting elements and detecting the intensity and spectral power distribution of light using the same light-emitting elements as spectrally sensitive photo detectors is disclosed.

SUMMARY OF THE INVENTION

The present invention provides an OLED element as claimed in claim 1. Embodiments of the invention are given in the dependent claims.

In accordance with embodiments of the invention an OLED element is provided that can be driven by a control unit in a first or a second mode. In the first mode a forward bias voltage is applied so that the OLED element emits light. In the second mode a reverse bias voltage is applied which has the same order of magnitude as the forward bias voltage. The current flowing through the OLED element is proportional to the incident daylight and is converted into a voltage by a transimpedance amplifier that virtually short circuits the OLED element.

In accordance with an embodiment of the invention, the OLED element is controlled by the control unit such that it is operated in the first mode except for short periods of time of less than 50 milliseconds not to be noticed by the eye of a user because of the persistence of vision. In these small periods of time the OLED element is operated in the second mode to detect the amount of incident light. By knowing the amount of incident daylight the power of the OLED element in the first mode can be adjusted to the incident light. In accordance with an embodiment of the invention, the OLED element is most sensitive to light with wavelengths between 3 IOnm and 410nm. In this spectral range, artificial light sources have only low emissions compared to the spectral range between 410nm and 700nm. Especially light emission levels of OLED elements themselves are low in this range. Contrary, natural daylight still has a large contribution in this spectrum range. Therefore, if the OLED element used as a photo sensor that measures a constant signal, it may be attributed only to the amount of natural daylight. The intensity of the daylight is directed proportional to the output voltage of the transimpedance amplifier. The output voltage can directly be used for further processing. This is based on the insight that the measured photo current is proportional to the light input. Thus, the power of the OLED element in the first mode can be adapted to the sensed amount of daylight. Advantageously, the complete surface of the OLED element can be used for emitting light in the first mode and detecting daylight in the second mode.

In accordance with an embodiment of the invention, the daylight-sensing OLED element is working in the second mode, measuring the amount of daylight. The control unit is supplied with the output voltage of the transimpedance amplifier, that is proportional to the amount of daylight. The control unit controls in dependency on the output voltage of the transimpedance amplifier another artificial light source. The precondition is that the spectrum of the artificial light source is negligible small at wavelength between 310nm and 410 nm. In one embodiment, the OLED element is most sensitive in this spectral range. When the spectrum of the artificial light source is negligible small at this range only the daylight is sensed. This is the case for a great variety of artificial light sources e.g. light bulbs, simple fluorescent lamps, high pressure sodium lamps, low pressure sodium lamps, light emitting diode (LED) lamps or further OLED lamps.

In accordance with an embodiment of the invention, the controlled artificial light source illuminates a room. The OLED element senses the power of daylight in the illuminated room. The control unit controls the power of the artificial light source in dependency on the sensed amount of daylight. By using this system the power of the artificial light source can be reduced in the presence of daylight and increased as the amount of daylight decreases. Thus, energy can be saved and a constant illumination of the room can be achieved.

In accordance with an embodiment of the invention, the control unit controls a luminous advertising. The control unit switches the luminous advertising on when the daylight power sensed by the OLED element decreases. Since artificial light sources don't have any effect on the sensing OLED element, the illumination of the advertising is not influenced by other artificial light sources as street lighting, cars or its own illumination.

In accordance with an embodiment of the invention, the control unit manages the thermal efficiency of a building comprising a heating system and an air conditioning system. By sensing the power of daylight with the OLED element the system can be adjusted to a day and night cycle and to sunny or cloudy days.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following embodiments of the invention are described in greater detail by way of example only making reference to the drawings in which:

Fig. 1 is a circuit showing an OLED connected such that it can be operated in a first or second mode,

Fig. 2 is a diagram illustrating the emission spectrum of a white OLED, Fig. 3 is a diagram illustrating the OLED photo current per light power in dependency on the wavelength of the sensed light in nanometers of several OLEDs. Fig. 4 is a diagram illustrating the OLED maximal photo current per light power in dependency on the dimming level of a second light source.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following the same reference numerals are used to designate like elements throughout the various embodiments described below.

Fig. 1 shows a schematic circuit according to the invention, the OLED 100 being operable in a first or second mode. A control unit controls the switch 102 which controls in which mode the OLED is operated. In the first mode the operation voltage 104 is supplied to the OLED, in the second mode reverse bias voltage 106 is supplied to the OLED. The reverse bias voltage has reverse polarity compared to the operation voltage 104. The capacitor 108 is connected in parallel to the OLED 100 and represents an internal parallel capacity of the OLED which is virtually short circuited by the transimpedance amplifier 110. The sensing voltage 112 is proportional to the current flowing through the OLED and can directly be processed by a control unit. The switch 102 is automatically switched by a control unit. During most of the operation time it is in the position that supplies the operation voltage, the forward bias voltage, to the OLED. In this mode the OLED 100 emits light. For a short moment in time, which is short enough not to be noticed by the eye of a user (e.g. less than 50 milliseconds), the switch 102 is set to the position that supplies the sensing voltage, the reverse bias voltage, to the OLED. Then, the OLED 100 is connected to a sensing circuit according to this invention. The transimpedance amplifier 110 has a low input impedance and thus creates a virtual short circuit. It converts the short circuit current of the device which is in this case the photo current of the OLED 100 into the sensing voltage 112 which is directly proportional to the amount of light which falls on the OLED 100.

Fig. 2 is a diagram illustrating the optical emission spectrum of a white OLED 100 in dependency on the wavelength in nanometers. It is used as a photo sensor in accordance to an embodiment of this invention. The highest emission peak has a wavelength of approximately 610nm. In the range of wavelengths from 450nm to 600nm and from 630nm to 680nm the OLED 100 emits less light. It has no emission in the wavelength range between 310nm and 410nm where the photo sensitivity is highest (cf. fig. 3). This spectral range is the deep blue visible and UV light. Other kinds of OLEDs 100 also don't emit in this spectral range. Contrary, natural daylight still has a large contribution in this range.

Fig. 3 is a diagram illustrating the photo current per light power of several OLEDs 100, scaled to maximum value in dependency on the wavelength in nanometers when the OLEDs 100 are sensing the incident light according to an embodiment of the present invention. The highest photo current is measured in a range of wavelengths between 340nm and 410nm which corresponds to the color in the far blue to the near UV. Many artificial light sources, e.g. light bulbs, simple fluorescent lamps, high pressure sodium lamps, low pressure sodium lamps, light emitting diode (LED) lamps and further OLED lamps emit only small amounts of light in this spectral range. Contrary, natural daylight still has a large contribution to this range. The photo current of the OLEDs 100 is negligible small for wavelengths above 450nm. Therefore, if the OLED 100 used as a photo sensor measures a constant signal, it may be attributed only to the amount of natural daylight. The intensity of the daylight is directly proportional to the output of the amplifier 110 that can directly be used for further processing.

The fact that an OLED 100 emits light of wavelength above 450 nm and detects light with wavelength in a range between 310 and 410 nm makes it possible to sense only the amount of daylight the OLED 100 is exposed to. Fig. 4 is a diagram illustrating the maximal photo current per light power of an OLED 100 in dependency of the dimming level of a second light source emitting UV light. Different reverse bias voltages are applied, from OV to 5V. It can be seen that the photo current increases with higher reverse bias voltages. The relation between the maximal photo current per light power and the dimming level of the second light source is proportional. The fact that the measured photo current is proportional to the light input makes it possible to use the output of the amplifier 100 in fig. 1 as data for the amount of incident daylight. LIST OF REFERENCE NUMERALS:

100 organic light emitting diode

102 switch

104 operation voltage

106 reverse bias voltage

108 capacitor

110 transimpedance amplifier

112 sensing voltage

Claims

CLAIMS:

1. An apparatus comprising a control unit and daylight sensing means comprising an OLED element (100) for providing a daylight sensing signal to the control unit, the control unit performing at least one control step in dependency on the power of daylight sensed by the OLED element.

2. The apparatus of claim 1, wherein the OLED element is controlled by the at least one control step.

3. The apparatus of claim 2, wherein the control unit is adapted for switching the OLED element between a first mode and a second mode, the OLED element emitting light in the first mode and sensing daylight in the second mode.

4. The apparatus of claim 1 , wherein the at least one control step controls at least one external apparatus.

5. The apparatus of claim 4, wherein the at least one external apparatus is controlled by the at least one control step for maintaining a constant illumination in a room.

6. The apparatus of claim 4, wherein the external apparatus manages the thermal cycling of a building.

7. The apparatus of claim 4, wherein the external apparatus is artificial illumination means not detectable by the OLED element.

8. The apparatus of any one of the preceding claims, wherein the OLED element is adapted for sensing light in the range from 3 IOnm to 410nm.

9. The apparatus of claim 4, wherein the external apparatus is a heating system, an air conditioning system, a luminous advertising, a shade or a blind.

10. A method for operating an apparatus of any one of the preceding claims, wherein the control unit performs a control step in dependency on the power of daylight sensed by the OLED element.

11. The method of claim 10, wherein the OLED element is switched by the control step between the first mode and the second mode, the OLED element emits light in the first mode and senses daylight in the second mode.

12. A computer program product comprising machine executable code for executing on a controller, wherein the computer program product performs the methods of claim 10 or 11.