Reflective Color Sensing with Avago Technologies' RGB Color Sensor - White Paper

Reflective color sensing is typically realized through photodiodes with multiple illuminant or photodiodes coated with color filters with single illuminant. This paper presents the concept of reflective color sensing using an RGB color sensor. First, reflective color sensing theory and the basic elements will be discussed. Then, we will continue on the hardware design consideration and how the sensor output can be interpreted. There are three important elements in reflective sensing: detector, target and illuminant. Detector is a device that captures light reflected from an object. Target is an object whose color is measured, like colored paper or paint. It is typically non-emissive, reflects and absorbs different amounts of light at different wavelengths. Illuminant is a light source whose spectrum covers the visible wavelengths, like sunlight. In a reflective color sensing system, the detector and illuminant is usually mounted together in a module. When the module is placed close to the target, light from the illuminant will fall onto the target surface and reflect back to the detector. The color of the light reflected off the surface is a function of the color of the surface. For example, white light, focused onto a red surface, is reflected as red.