This note lists and answers common technical questions about the operation of Light in Motion’s IR hermetic components.

What is the greatest distance at which an infrared solution will still work?
There is no absolute answer to this question. It depends much on the application. In most cases, by pulsing the emitter with a high drive current and using a sensitive photosensor, such as a photodarlington, one can expand the range.
  • The range for detecting an object by reflection can be from 0 mm to 400 mm. The factors involved are the configuration and reflectivity of the reflective surface, the drive current of the emitter, and the photosensor output. Dust, however, can impair this range.
  • Object sensing by transmissivity (ie. breaking a beam of light between two points with an object) has a range of 0 to 12 m. The factors involved are the size of the object used to break the beam, the drive current of the emitter, the output type of the photosensor, and the electrical timing techniques used such as synchronous detection.
  • For pure data transmission, the range is from 0 to 15 m. The factors are the data rate, the coding and modulation technique, and the expected signal to noise ratio or bit error rate. A high emitter drive current can improve the range of the system.
Can IR photosensors detect visible light ?
Yes. All of the Light in Motion photosensors are constructed using silicon chips. Silicon has a relatively flat sensitivity range and can detect the entire visible spectrum. The sensitivity, however, decreases from red wavelengths (660nm) to blue wavelengths (450nm).
What is the most efficient Light in Motion emitter ?
The brightest emitter we offer, in terms of on-axis intensity, is the F5D1. This emitter has a narrow emission angle. If a wider emission angle is preferred, the F5E1 is recommended.
What is the response time of Light in Motion emitters and photosensors ?
Each component type has a different response time which we specify as rise time or fall time. The typical rise times for each product family are given below.
  • 940 nm emitters: 1 gs
  • 880 nm emitters: 0.8 gs
  • Phototransistors: 10 gs
  • Photodarlingtons: 100 gs
  • Logic Output Photosensors: 0.1 gs
What is the maximum driving current of Light in Motion’s emitters ?
The answer to this question depends on the type of emitter and the forward current conditions. Driving conditions can be either continuous or pulsed. The continuous maximum current is specified in the data sheet of the product. The maximum pulsed current depends on the pulse width and the duty cycle. The duty cycle is determined by dividing the pulse width by the period of the pulse. The pulsed current can range as high as two amps if the pulses are very short and the duty cycle is very low.
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