Bar graph arrays are light emitting diodes (LEDs) that are used for solid state metering in applications such as audio monitoring, telecommunications, and instrumentation. These rugged board-mounted components are usually rectangular, X-Y stackable, and available in up to ten segments. Bar graph arrays with interlock mechanisms can be connected together in order to display long strings of information. Many devices feature easy-to-handle integrated circuit (IC) packages that are compatible with standard dual in-line package (DIP) sockets. Bar graph arrays that contain multi-color elements help eliminate many of the alignment, intensity, and color-matching problems associated with discrete light emitting diodes (LEDs). Consequently, they are often used in transportation, push button, and security applications that require easily recognizable segments, a wide viewing angle, and high on/off contrast.
Bar graph arrays include one or more red, green, yellow, or white light sources. Red light bars are available with product names such bright red, high efficiency red, and ultra red. Suppliers who combine red and yellow lights can provide orange or super orange lights Color names such as high performance green, high performance yellow, super lime green, and super line yellow are also available. Typically, LED dye materials include a combination of gallium (Ga) and other elements such as silicon (Si), nitrogen (N), or arsenic (As). Electrical and optical characteristics for bar graph arrays include peak wavelength, dominate wavelength, spectral line half width, capacitance, forward voltage, and reverse current. Absolute maximum ratings for bar graph arrays include power dissipation, DC forward current, forward current per chip, peak forward current, reverse voltage, operating/storage temperature, and lead solder temperature. Some bar graph arrays are suitable for low-level indicators. Others provide low current operation.
Important specifications for bar graph arrays include luminous intensity and dominant wavelength. Luminous intensity, which is typically expressed in candelas (cd) or lumens per steradian (lm/sr), measures the given direction of a source that emits monochromatic radiation with a frequency of 540 x 1012 Hz and that has a radiant intensity on the order of 1/683 w/sr. Together with the CIE photometric curve, luminous intensity provides the weighting factor needed for conversions between radiometric and photometric measurements. The dominant wavelength is derived from the CIE chromaticity diagram and is that single wavelength which defines the color of the device. The CIE system characterizes colors by a luminance parameter Y and two color coordinates, x and y, which specify the point on the chromaticity diagram.
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