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The monchromatic sensors are less expensive, generally under $500. While they have the price advantage, they have several
disadvantages. Their ability to sense various colors is limited. For example a red LED cannot effectively be used to sense a red mark on a white background. Similarly a green LED cannot
sense a green mark on a dark background. The various color combinations and backgrounds must be considered in the selection process. Sometimes seperate red and green LED's can be used
together in a process to accomplish the color discrimination task. Another disadvantage of the LED systems is that they do not perform well in discerning slight changes in color or
hue. Thirdly, they are sensitive to changes in ambient light and variations in distance of the colored item. Since the sensor evaluates the amount of the monchromatic light that is received,
either changes in the light conditions or distance to the object effect the amount of light received.
The RGB systems typically use a ratio approach to compare the strenght of red to green to blue. Using this method, the system is able to
discriminate small changes in color or hue of any color, and the distance to the colored object is less of a factor. Ambient light changes can still effect the units accuracy but not nearly as much
as with the monochromatic systems.
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