Abstract: A fast acting electromagnetically operated shutter for protecting an imag system from damaging light, such as intense laser light, comprised of a plurality of vane type shutters driven by magnetically moveable linear racks transferring linear to rotary motion to the midportion of each vane to aid in overcoming inertia. The linear racks are comprised of an upper rack at one end of the shutters and a lower rack at the opposite end of the shutters wherein both upper and lower racks simultaneously move reciprocally together. The racks have gear teeth thereon that are meshed with alternate vanes from first the upper and then the lower racks to transfer opposing directional rotation to adjacent vanes. An electronic shutter control means responds to input damaging light intensity signals impinging light detecting sensor means.

Abstract: Optical sensor has divergent light from a source, preferably from a single optical fiber, and a lens which collimates the light into a broad beam. The broad beam is acted upon and passes to another lens which focuses the beam onto a single optical fiber for detection. The beam is acted upon by reflecting off of a surface when the surface is dry or dissipating when the surface is wet, or is acted on in other ways to interrupt the beam to provide a water presence signal or the like.

Abstract: A switching matrix enables switching of optical signals from any of a plurality of optical input paths to selected optical output paths, without requiring physical re-connecting of the inputs or outputs. Plural broad-band optical waveguides are defined preferably in otherwise non-transmissive quartz crystalline wafers, to provide relatively high signal isolation. The wafers are fused to electronic shutter windows situated in an array and discretely operable under processor x-y address control. Optical signals passed through actuated electronic shutter windows are summed in output wafers, having waveguide structure generally reverse to that of the input quartz wafers. Through selected segment actuation, optical signals from selected optical input paths may be transmitted or blocked at the electronically controlled shutter array, for being output on selected optical output paths. Alternatively, fiber optic bundles may replace input or output quartz wafers.

Abstract: An optical encoder produces a reference signal and compensates for any instability in intensity of a light source which reads the encoder. The optical encoder comprises a movable encoding element having an analog track of variable transmissivity, and a chopping element for alternately transmitting light from the source through the analog track and around the analog track. Light transmitted through the analog track comprises an information signal and light transmitted around the analog track comprises the reference signal. The chopping element comprises an optical switch or a rotatable or stationary element havnig an alternating series of opaque and transparent sections.

Abstract: A displacement detector in accordance with the present invention is for detecting the amount of displacement of an object to be measured, and comprises sensing means arranged side by side with predetermined spacing whose states change in response to the changes in electromagnetic energy such as light energy, magnetic energy, and electrical energy, an electromagnetic energy generating means for generating electromagnetic energy, an electromagnetic energy transmitting means that is linked to the motion of the object to be measured, for transmitting the electromagnetic energy from the electromagnetic energy generating means to the sensing means that is situated at the position that corresponds to the displacement of the object to be measured, a conversion unit for outputting the detection signal obtained from the sensing means at the position where the electromagnetic energy is changed by the electromagnetic energy generating means, as a displacement detection signal, by converting the detection signal to a code

Abstract: An improved vehicle height sensor and automotive leveling system are described using, in a preferred embodiment, two optical emitter-receiver pairs mounted in the sidewall or dust cover of a standard automotive air shock. The emitter-receiver pairs are arranged to operate by reflecting light from the central shaft of the shock absorber. Each emitter-receiver pair provides a light path that lies in a plane substantially perpendicular to the extension direction of the shock. The two emitter receiver pairs are spaced apart along the extension direction of the shock. Movement of the internal piston of the shock successively interrupts (by absorption) the light paths of the emitter-receiver pairs so as to provide a positive indication of the location of the movable piston and hence the height of the shock and the height of vehicle body above the road. The emitter-receiver pairs are mounted in a common assembly and seal to the shock dust cover through a single hole.

Abstract: A snap acting fiber optic switch in which a carrier operates between two stop surfaces separated by a wedge shaped gap. A planar shutter perpendicular to the stop surfaces extends from an end of the carrier at the wide end of the wedge shaped gap into a gap between opposing end faces of a pair of optical fibers aligned with an axis perpendicular to the plane of the shutter. A plunger actuated over center snap acting mechanism biases the carrier toward one or the other of the stop surfaces, depending on the position of the plunger.

Abstract: An optical rotary encoder eliminates the necessity of relatively positioning a code plate and a click mechanism therefor so that it can be assembled with ease. The code plate is mounted for rotation relative to a stationary plate member, and the click mechanism including a ball and a spring plate is interposed between the code plate and the plate member so that all the members can be incorporated as a single device.

Abstract: An optical sensor comprises a sensor circuit having parts which are optically interconnected with each other through an optical interconnection board interposed therebetween. The interconnection between the sensor circuit parts is thereby simplified remarkably, so that the mass-producibility of the sensor can be increased to lower its manufacturing costs.

Abstract: This invention relates to an optical switch device including a light spot composed of a fluorescent substance in combination with a radioactive element. A switching signal is obtained from an output from a light detector.

Abstract: A dust and water tight electric pressure switch that is highly visible, even in a smoke filled area, includes a lightguide disc disposed between a ring-like cover and a cylindrical housing disposed behind a slightly depressible flexible zone at the center of the disc. The flexible zone covers the open front end of the housing. The disc is constructed of a light-collecting polycarbonate and is formed with relatively small light radiating surface to produce high contrast at the latter. Disposed within the housing is a contactless switch arrangement including a plurality of so-called light barrier units arranged about a light source, and an actuator extending from the rear of the flexible zone. A light shield carried by the actuator controls the amount of light which impinges on the light barrier units as a function of the position of the actuator as determined by how much the flexible zone is depressed.

Abstract: A combination electro-optic sensor and switch including a printed wiring board supporting an electro-optic sensor enclosed in a sealed housing, a sleeve mounted on a shaft for rotation within the housing in the light path the electro-optic sensor with a portion of the shaft extending through the sealed housing and connected to a wire actuator, the engagement of the wire actuator by a copy sheet providing an approximately 20 millisecond response time of the sensor.

Abstract: A magnetically responsive reed switch assembly having one or two cantilevered reed members arranged to close and open a gap responsive to respective levels of magnetic exposure, supports two optical fiber members in end-to-end closely spaced confrontation with the common axis alignment or misalignment of the fibers being a function of the relative closed or opened gap condition. A convenient method of fabrication involves mounting opposing cantilevered reed members on a substrate which is bent to bring the reed members closer together longitudinally. While so bent, a gap closing magnetic field is generated and a continuous length of optical fiber is bonded to the flat aligned surfaces of the reed assembly. The fiber is scored, broken at scoring, and stress and magnetic field is relieved, whereupon fiber ends shift laterally to produce open circuit condition.

Abstract: A satellite defends itself by having a plurality of corner cube retroreflectors with shutters, each having a laser light sensor. It is assumed that the attacker first must obtain positional and range information with a pulsed laser. When one of the sensors detects these low power laser pulses, it causes the shutter of the corner cube array to open and return the pulses with sufficient strength to saturate or damage the attack sensors.

Abstract: A photo-coupler with delay function includes a fluorescent substance, a light-emitting diode disposed at one end of the fluorescent substance and a phototransistor disposed at the other end of the fluorescent substance. While a light emitted from the light-emitting diode is impinging on the fluorescent substance, it emits a fluorescence. The fluorescent substance emits a phosphorescence after an emission from the light-emitting diode is interrupted. In this arrangement, when the fluorescent substance is displaced with an operating plate, the light intermittently emitted from the light-emitting diode impinges on the fluorescent substance. The phototransistor selectively detects the light intermittently emitted from the light-emitting diode, the fluorescence and the phosphorescence both continuously emitted from the fluorescent substance.

Abstract: A manually operable touch pad for generating steering signals and enable signals for manipulating an image on a CRT display or for controlling the operation of plural motors whereby the image or object being driven can be positioned using appropriate hand/eye coordination. The touch pad comprises a box-like mounting base supporting a rectangular printed circuit board on which are mounted four opto-switches centered on the respective edges thereof. The printed circuit board also supports other circuit components and the necessary interconnecting conductors. Overlaying the base in covering relation with respect to the printed circuit board is a molded plastic top having a center post which depends downwardly from the underside thereof, passing through an apertrue in the printed circuit card and adaptive to be secured to the center of the base by a flexible coupling.

Abstract: A rotary type photoelectric switch comprises a rotary shaft rotated by an external force, a light interrupting plate coupled to the rotary shaft, a light-emitting element for emitting light, and a light-receiving element for receiving the light of the light-emitting element, wherein the light interrupting plate swings to enter into and exit from the lightpath formed between the light-emitting element and the light-receiving element. A stopper remote from the rotary shaft regulates the stroke of the light-interrupting plate, and a wavy spring or magnet reduce bounce of the plate.

Abstract: A displacement detector in accordance with the present invention detects the amount of displacement of an object to be measured. Sensing means are arranged side by side with predetermined spacing whose states change in response to the changes in electromagnetic energy such as light energy, magnetic energy, and electrical energy. An electromagnetic energy generating means and an electromagnetic energy transmitting means that is linked to the motion of the object to be measured, transmits the electromagnetic energy from the electromagnetic energy generating means to the sensing means that is situated at the position that corresponds to the displacement of the object to be measured. A conversion unit ouputs the detection signal obtained from the sensing means as a displacement detection signal, by converting the detection signal to a coded signal that is characteristic of the position of the sensing means for the position where there was a change in the electromagnetic energy.

Abstract: A relative movement sensor that may be used to measure the force applied to a beam, for example to provide an onboard weighing system for a truck. The sensor measures relative movement between first and second portions of the beam, and includes a housing connected to the first portion and a mounting block connected to the second portion. An optical source and a pair of optical detectors are secured to the housing. A line between the first and second portions define a first axis, and a line between the source and a point midway between the detectors defines a second axis. The mounting means mounts a beam modulator between the source and detectors, such that relative movement as between the first and second portions results in movement of the beam modulator with respect to the housing. A measurement circuit provides an output signal corresponding to the relative illumination falling on the detectors.

Abstract: An optical information processing device includes a light receiving and driving circuit including photo voltaic elements adapted to receive an incident light and to produce a drive voltage, and an optical shutter driven by the drive voltage produced by the light receiving and driving circuit. With this structure, various basic logical operations are performed by the device according to the present invention. As a feature of the invention, the device receives a pair of incident lights having a complementary relation in strength with each other and produces a pair of output lights from the optical shutters which also are complementary in strength with each other. Thus, the possibility of errors in logical operations is greatly reduced.

Abstract: A push-button switch including a housing, at least one pair of push-buttons movably mounted in the housing, a plurality of light-emitting elements, a plurality of photo-sensors arranged to receive light from the light-emitting elements and light blocking members on the push buttons for selectively blocking light received by the photo-sensors. The buttons are spaced apart in a longitudinal direction and each includes a light blocking member which is movable with the push-button from a non-operating position to a plurality of signal sending positions in a vertical direction perpendicular to the longitudinal direction. The light-blocking members are spaced apart in a lateral direction perpendicular to the longitudinal and vertical directions and overlap in the longitudinal direction.

Abstract: An optical switch for use as a modular keyboard switch designed to provide tactile and audible feedback to the keyboard operator. The switch includes an opaque housing in which a light emitting device and a light activated detector are mounted. A "U" shaped spring shutter rests within the housing between the emitter and detector and has an aperture through which light from the emitter may illuminate the detector. A spring loaded key stem moves longitudinally within the housing and is designed to penetrate the open end of the shutter. The key stem and shutter are shaped such that as the key stem is depressed the upwardly extending arms of the shutter are at first forced outward by projecting shoulders on the key stem and then snap back along upwardly sloping surfaces of the shoulder, thereby causing the shutter to spring upwards and block the optical path between the emitter and detector. The snap action of the shutter causes an audible "click" and also provides tactile feedback to the operator.

Abstract: An optical controller device employing a single rotatable light blocking plate on opposite sides of which are mounted light emitting and light receiving elements. A pattern of openings or transparent areas arcuately arranged on different circumferences of the light blocking plate determine the passage or interruption of light and thus provide output signals according to the position of rotation of an operator's handle connected to the light blocking plate. The light emitting and receiving elements are mounted on support plates configured so that a first group of the light emitting and receiving elements and a second group of the light emitting and receiving elements are symmetrically disposed on opposite sides of a centerline of the light blocking plate.

Abstract: This invention relates to an optical switch device including a light spot composed of a fluorescent substance in combination with radioactive elements or a pattern of a plurality of light spots and light detectors each manually moved relative to the light spots to detect a fluorescence from each fluorescent substance. An on-off pattern switching signal or a codified switching signal is obtained from an output from each light detector.

Abstract: An optoelectronic array or system permitting the simultaneous input of six isplacement components is housed in a plastic sphere wherein a fixed slit diaphragm is connected in series to each of six light-emitting devices, which are arrayed in a plane at equal angular displacements from each other. The light-emitting devices are arrayed opposite corresponding linear one-dimensional position-sensitive sensors, whose axes are aligned vertically to the direction of the slits of the corresponding slit diaphragms, so that the light-emitting devices with their corresponding slit diaphragms are adapted to move relative to the position-sensitive sensors. The individual light-emitting device allocated to each sensor is driven by an electronic controller which maintains the sum of both currents flowing in the corresponding position-sensitive sensor constant and equal for all six sub-systems and additionally regulates the radiant intensity of the light-emitting devices.

Abstract: A matrix keypad is rendered intrinsically safe by use of a circuit employing a plurality of opto-couplers powered by a single intrinsically safe (IS) barrier.

Abstract: A switching device includes a contact movable between two positions, to selectively open and close an electrical path, and a multicolor light emitting diode for indicating different positions of the contact by respectively different colors. The multicolor light emitting diode directs a light beam which is reflected from the contact in accordance with its position on one of two light sensors. The color of the light beam is controlled in accordance with the outputs of the light sensors.

Abstract: A fiber optic switching system for industrial control sensing applications includes a link monitoring capability for detecting faults in the fiber optic cable. Two transmitters of different wavelengths are coupled into a single fiber. The switch utilizes an optical filter which when inserted in the optical path blocks one wavelength of light but allows the other to pass through. The absence of all light in the switch output indicates a fault and the presence or absence of the filtered-out light is used to determine the switch state.

Abstract: A joystick device disclosed has a plurality of light emitter-detector devices disposed around a control shaft in a casing supporting the shaft. A first blocking member on the control shaft selectively blocks out the light to one or two detectors which produces a change in electrical state at an output terminal of a signal processing circuit connected to each detector without the use of any physical contact or the use of mechanically operated electric switches. A second blocking member on an axially movable inner shaft actuated by a button interrupts the light from another light emitter-light detector device having a similar signal processing circuit. The output circuit connects to a plug-type connecting member that connects to a load device such as a joystick-operable computer or video game.

Abstract: An electromechanical control for use with a joystick lever which swivels along x and y axes simultaneously. The control has a light source and two light sensitive phototransistors. The light source emits a beam which is split into two parts. A light control sector is pivoted on the base, and mechanically linked to the lever. The sector is disposed in the paths of the two parts of the split beam, and has two arcuate translucent portions, each translucent portion being on its own radius and the portions having a common center. One part of the beam passes through one translucent portion and the other part of the beam passes through the second. The phototransistors are disposed on that side of the translucent portions opposite the location of the light source. The one translucent portion has a graduated opacity along its length, such that the light arriving at one phototransistor varies as the sector pivots by movement of the lever.

Abstract: A sensor for determining image brightness in the viewing-ray path of a microscope is so utilized as (1) to control the intensity of light for object illumination and (2) to black out or darken the viewing-ray path while switching optical elements such as from one to a selected other of a plurality of turret-mounted objective lenses. The arrangement assures that an observer will not be dazzled by sudden brightness in the course of lens switching or in the course of switching from use of one to use of another of a plurality of contrasting methods.

Abstract: A switching device includes a contact movable between two positions, to selectively open and close an electrical path, and a multicolor light emitting diode for indicating different positions of the contact by respectively different colors. The multicolor light emitting diode directs a light beam which is reflected from the contact in accordance with its position on one of two light sensors. The color of the light beam is controlled in accordance with the outputs of the light sensors.

Abstract: The invention relates to a joystick control unit featuring a joystick shaft member with a reflective surface on its bottom portion which is parallel to the X-Y plane when the shaft is placed in a centered upright position. The reflective surface tilts as the shaft member is moved through the X-Y plane and reflects the radiant energy emitted from a source mounted beneath the shaft member and directs it towards a plurality of radiant energy detectors selectively arranged beneath the reflective surface. The shaft member includes a movable inner member with at least one aperture in an upstanding sidewall which selectively permits or prevents the transmission of radiant energy through the aperture for purposes of controlling a switch function.

Abstract: A force controller wherein lateral, axial and rotational force on a handle (10) are opposed by bending, extension, compression and torsional forces in a tubular flexure element (12) that includes lateral rings (92a . . . 92n) and longitudinal beams (96a . . . 96n-1). A translating plate (23) is controlled in accordance with the torsion and deflection of flexure element (12) to provide optical control signals from code element (56) and read head (64) for three axes of motion. Axial forces on handle (10) cause extension or compression of flexure element (12) which is linked to fin (42). Pivotal movement of fin (42) in response to such extension and compression provides optical control signals from code element (72) and read head (74) for a fourth axis of motion.

Abstract: An image signal generating apparatus includes an optical system for focusing the image of a photographic film onto a predetermined plane and a scanning device for scanning the image with a photoreceptor positioned at the predetermined plane and generating output signals representing the light intensity distribution of the film. The scanning device performs a first scan of the image and a second scan of the image upon completion of the first scan. During the first scan the levels of the output signals indicative of the maximum density and the minimum density of the film are detected, and during the second scan the exposure of the photoreceptor is controlled in accordance with the detected levels. Also, during the second scan, the output signals are clamped to a clamp level calculated in accordance with the detected maximum density level and the minimum level of the output signals during the first scan.

Abstract: A lock with mixed mechanical and electrical control which utilizes a key device which includes mechanical notching for cooperatively engaging pistons carried within the lock stator and rotor and which also includes a signal emitter which is selectively alignable with a signal receiver which activates an electro-mechanical drive which is operatively connected to control the locking and unlocking of the lock bolt when the key device is at a position of the rotor which is different from the position at which the key device is introduced into the rotor.

Abstract: An optical mouse for inputting a cursor position including first and second line patterns formed on opposite surfaces of a transparent substrate, with the lines of the first and second line patterns being perpendicular. The line patterns are illuminated by a light source in the movable mouse body, which also includes an optical system and detecting elements for separately detecting light reflected from the first and second patterns. Because the first and second line patterns are located at different distances from the optical system, light reflected from the two patterns can be separately focused to prevent interference between the two patterns.

Abstract: An optically activated keyboard provides inputs to a digital computer or the like. The keyboard includes a key housing having formed therein a wave guide matrix of intersecting columns and rows with light emitting diodes (LED's) installed in one end of each column and photo transistors installed in one end of each row. A plurality of keys are mounted at the top surface of the housing, each key having a plunger which projects through a corresponding aperture in the housing, when the key is depressed. The intersections of the columns and rows are located directly beneath the apertures so that when a key is depressed, its plunger intrudes into the volume at the intersection. Each plunger, in concert with the wave guide intersection, forms a light polarizing system. In the preferred embodiment, each plunger has a reflecting face that is angled to reflect light from the LED in the corresponding column into the corresponding row, finally impinging against the appropriate photo transistor.

Abstract: A multi-position rotary switch comprises an actuator drum divided into a plurality of different n-bit codes where each bit is represented by a reflective area or a non-reflective area on the drum. The drum is radiated by a suitable emitter and radiation reflected off of the drum by reflective bits is detected by a plurality of radiation detectors. The drum is rotatable to bring the different n-bit codes into view of the radiation detectors. Each different n-bit code detected by the radiation detectors is indicative of a particular switch position.

Abstract: A switch including a rotor within a housing with the housing including a circular array of phototransistors. The rotor includes light transmission means such as a fiber optic which transmits light from a centrally located diode to a selected phototransistor. Each phototransistor is in circuit with a power source and with an output lead. A detent retains the rotor against undesired movement.

Abstract: A touch-sensitive key has a radiation-propagating prism or plate between a radiation source and a radiation detector. Radiation is scattered from a top surface of the prism or plate so as to reach and activate the detector through a side surface when the top surface is touched. External radiation is free to enter the prism or plate and to leave through the side surface but this radiation is not capable of actuating the detector. In one embodiment the detector is spaced from the side surface so that it cannot be reached by external radiation. In an alternative embodiment, external radiation is subject to multiple reflections within the prism or plate and at each reflection part of the radiation is transmitted through the pertaining surface to be absorbed in a substrate layer.

Abstract: A noiseless rotary detent switch, wherein a ferromagnetic projection passes in close proximity to a magnetic pole, in combination with a first photoelectric detector for detecting the leading and trailing edges of said projection and a second photoelectric detector for detecting the presence or absence of said projection, the magnetic attraction between said projection and said pole providing the noiseless detent action and said first and said second photoelectric detectors providing electric signals for actuating switches in a sequence corresponding to that of the direction of rotation of said rotary switch.

Abstract: Fluorescent optical switch and keyboard apparatus wherein a plurality of fluorescent optical key switches are arranged in a matrix array of rows and columns with a key disposed at each column-row intersection and wherein each key carries a fluorescent optically reflective element thereon. A single optical photo-diode disposed at each key location is caused to operate in three discrete modes with respect to the fluorescent element. In one mode the diode emits light which is caused to be reflected upon key when the key is depressed. In another mode the reflected light striking the diode causes the diode to act as a photo-receptor effectively indicating key actuation.

Abstract: A non-contact switching device comprising a housing, a light path switching member housed within the housing, an actuator member disposed in the housing for transferring an external mechanical force to the light path switching member, a light entrance member disposed on the housing connectable to a first optical fiber for guiding light transferred from an external light source through the first optical fiber to the light path switching member, and a light exit member disposed on the housing connectable to a second optical fiber for guiding light from the light path switching member to the second optical fiber, the light path switching member being associated with the actuator member so as to switch a light path from the light entrance member to the light exit member through the light path switching member.

Abstract: A fiberoptic limit switch system comprising a light source, an optical beamsplitting arrangement, a switch, an optical fiber, a detector, and output circuitry. The light source is a light-emitting diode. The switch is responsive to external stimulus. The switch comprises a housing, a receptacle for receiving the optical fiber, and a reflective surface movable between two positions within the housing. The optical fiber extends from the light source to the switch. The detector is arranged so as to receive light from the optical fiber and transmit a signal relative to the light emission. The output circuitry is electrically connected to the detector.

Abstract: A joystick controller for use with a home electronic video game produces electrical control signals in response to manipulation of a control stick. Within the controller housing a pair of light sources produce orthogonal light beams which are detected by respective light detectors to produce the control signals. A shutter, actuated by movement of the control stick, regulates the light falling onto the light detectors to produce control signals indicative of control stick positions.

Abstract: A photoelectric key switch device for preventing error of the output timing of electrical signals from a group of light-receiving elements, while operating an electric processing unit by signals that are simultaneously produced. The device is provided with a rotor having a notch that forms optical paths between the elements of a group of light-emitting and light-receiving elements, other than one set of elements, when a key is inserted into the rotor and the rotor is rotated through a pre-determined angle. Another notch forms an optical path between the set of elements and the aforementioned one set of elements when the rotor is additionally rotated through an angle .alpha..

Abstract: A light valve has a pair of rotating vanes for controlling the cross section of a light beam passing between the vanes. The vanes rotate on corresponding shafts, each controlled by its own integral motor. Separate feedback control systems produce electrical control signals to each motor for rotating each shaft independently of the other to control the desired phase angles of the vanes. In one embodiment, both motors are permanent magnet direct current servo motors in which the wound armature is an integral part of each shaft. A stationary magnetic field generated by permanent magnets is common to both motors. Power is supplied to each armature by a pair of thin, parallel, flexible, electrically conductive strips extending from an end of each shaft. The conductive strips reduce the torque on the shaft when twisted during operation. In one embodiment, the control system produces a calibrated digital control signal from a PROM representing the desired phase angles of the rotating blades.

Abstract: An electronic circuit module and a compatible module holder are provided which are particularly suitable for magnetic bubble memory applications. The holder has power-down warning and write-protect circuits utilizing light emitting diodes (LEDs) and photo-transistors to detect motion prior to removal of the module, and to detect the presence of a reflective sticker to write enable, respectively. Moreover, the module has separate ground buses for each power supply voltage to prevent circuit damage due to relative polarity reversal in case of ground non-connection upon insertion or removal of the module from the holder.

Abstract: A sensing apparatus wherein a photoelectronic transducer and a light-emitting diode are adjacent to one end face of a bundle of fiber optics. The other end face of the bundle is located in the housing of an actuator wherein a reciprocable plunger can move a light absorbing or light reflecting element into and from the path of light issuing from the bundle. The position of such element influences the amount of light which is reflected back into the conductor to ensure that the signal which is generated by the transducer is indicative of the amount of reflected light. The transducer can transmit signals to a signal receiving device which, in turn, can influence the intensity of light issuing from the diode in dependency upon whether or not the device receives a signal from the transducer. The actuator can be installed in an area which is not explosion-proof or in an area which is exposed to pronounced electrical noise.