Image Credit: Autonics USA, Inc.

Light emitting diodes (LED) are PN junction devices that give off light radiation when biased in the forward direction. Most light emitting diodes function in the near infrared and visible ranges, though there are now UV LEDs.

Configuration

Digital LED displays can have a common anode or common cathode configuration.  In a common anode configuration all the segments in the LED share one anode pin. In a common cathode configuration all the segments in the LED share one cathode pin.  Common cathode is the "standard" circuit where the cathode is connected to the "common" point on the circuit, usually ground, and usually through a resistor, which is often bypassed with a capacitor, placing it at "AC" ground potential.

Digital LED displays are highly versatile and well suited to a variety of measurement applications. Digital LED displays can be numeric or alpha numeric.  Numeric displays display numbers only, alphanumeric displays can display numbers and letters.  Types of displays include:

• Segmented
  • A seven-segment display can display numbers only.
  • A sixteen-segment display can display numbers and letters.
• Dot matrix
  • A 4x7 dot matrix display can display numbers only.

  • A 5x7 dot matrix display can display numbers and letters.

Performance Comparison

Light emitting diodes are a reliable means of indication compared to light sources such as incandescent and neon lamps.

Specifications

Important display package specifications to consider when searching for digital LED displays include:

• Number of rows
• Number of characters per row
• Character height
• Color - Standard color choices for LEDs include:
  • Red
  • Yellow
  • High efficiency red
  • Orange
  • Green
  • Blue
• Wavelength - determined by the color of the LED
• Viewing distance - determined primarily by the minimum size requirements for objects that the user must see
• Viewing angles on the x and y-axis - the angle, in degrees, between a line normal to the display surface and the user's visual axis
• Minimum and typical luminous intensity - describes the luminous flux per unit solid angle, and its unit of measurement is the candela (cd).
• Case dimensions - The case or package of the display will have separate dimensions (width, depth, height) than the actual viewing area of the display.

Standards

BS EN 62341-1-1

BS PD IEC/TR 62728