the external device for this purpose the terminal pins 34 pass through the housing 12 to be received by a connector not shown leading to the external device incorporating the optical interrupter 10 the housing 12 may include mounting holes 35 or the like for attaching the housing 12 to the device with which the optical interrupter 10 will be used referring now to fig2 led 26 may be configured as a light transmitter emitting light 36 along axis 30 while led 27 may be configured as a light receiver receiving and detecting light 36 along axis 30 a vane 40 may periodically pass into slot 18 across axis 30 to block light 36 and out of slot 18 away from axis 30 to permit passage of the light 36 thereby changing the amount of light received and detected by the led 27 generally leds differ from other photo detectors such as photo diodes and phototransistors by their construction and often by the materials used in the leds leds may use direct band gap semiconductor materials as opposed to indirect band gap semiconductor materials in forming a pn junction typically the n doped material of the pn junction is attached to an opaque support being either or both of a heatsink or electrical conductor and light is emitted from the p doped material the pn junction is normally encased within a light transparent material such as a plastic that is either clear or tinted to match the color of the.