Abstract - reflective color sensing is usually realized by photodiodes with multiple light sources or photodiodes coated with color filters containing a single light source. This paper introduces the concept of reflective color sensing using RGB color sensor. Firstly, the reflective color sensing theory and its basic elements are discussed. Then the hardware design considerations and sensor output interpretation are discussed.

    There are three important elements: detector, target and light source. A detector is a device that captures light reflected from an object. The target is the object to measure color, such as colored paper or paint. Usually non emissive, it reflects and absorbs different amounts of light at different wavelengths. Illumination is a light source whose spectrum covers the wavelength of visible light, such as sunlight.

    In reflective color sensing systems, detectors and illuminators are usually installed together in one module. When the module is placed near the target, the light from the light source will fall on the target surface and reflect to the detector. The color of the light reflected from the surface is a function of the surface color. For example, white light focused on a red surface is reflected as red. The reflected red light is incident on the color sensor to generate R, G and B output voltages. By interpreting the three voltages, the color can be determined. Since the three output voltages increase linearly with the intensity of the reflected light, the color sensor can also measure the reflectivity of the surface or object.