Color Sensor | Principle | 5 Important Applications

COLOR SENSOR

Contents

What are color sensors?

Color sensors are a form of “photoelectric sensors” that uses a transmitter for emitting light and a receiver for sensing the light wavelengths that are reflected back to it. Generally, a color sensor is capable of detecting a combination of wavelengths belonging to the red, blue, or green spectrum. The combined analysis of these three wavelengths gives the actual color of the object or light. The color sensor is used for generating an output signal that has an energy corresponding to the incident light energy i.e. it measures the wavelength of light received.

What is the principle of a color sensor?

Color sensors can be of two types: one sensor type illuminates the given object with broad wavelength light comprising of all the red, green, and blue spectrum wavelengths, and then it detects the light wavelength that the object reflects back with the help of a receiver. The second sensor type illuminates the given object with specific red, green, and blue spectrum wavelengths, and then it detects the ratio of light wavelengths that the object reflects back to the incident RGB light wavelengths with the help of a receiver.

When light energy in the form of photons is bombarded on a metal surface, the free electrons present on the metal surface get excited and jump out of the metal lattice resulting in a flow of electrons or electric current. The amount of electric current generated is dependent on the energy of the photon or the wavelength of incident light. This is how the wavelength of the light reflected back is calculated. Electrons can emit from the metal surface if the wavelength of the light is less than or equal to a threshold wavelength. The threshold frequency corresponds with the minimum energy required to break the metal bonds by the electrons.

A red color object would only reflect the red light wavelength when a broad wavelength light is incident on it. Similarly, a white object would reflect the light of every wavelength and a black object would not reflect the light of any given wavelength.

optical sensor
Representation of bombardment of photons that emits electrons off a metal surface. Image source: PonorPhotoelectric effect in a solid – diagramCC BY-SA 4.0

Photodiodes are used for converting light energy into electron flow. Photodiodes are comparatively more sensitive towards the light having lesser frequencies (i.e. it can detect light from the infra-red spectrum more accurately than the light from the visible or UV spectrum). The working of a photodiode is similar to a P-N junction diode. However, in the case of photodiodes, a transparent lens is used in the place of an opaque casing that is used to focus light on the P-N junction. Most photodiodes are made up of materials like silicon and germanium. These diodes are sensitive to infrared light, and hence they are used in several medical applications.

Some color sensors also use photo-resistors. A Photo-resistor is also termed light-dependent resistors or LDR. These devices can vary their internal resistance depending on the amount of incident light energy. The greater the intensity of light, the lower is the resistance. When the light intensity incident on the LDR is more, the current generated or the electron flow is more, and hence, the resistance is less. Cadmium sulfide cell is a high resistance semiconductor material and is sensitive towards IR light, that is why these cells are commonly used in photo-resistors. In some cases, materials like lead selenide (PbSe), indium antimonide (InSb), and lead sulfide (PbS) are also used in LDRs. However, photo-resistors require a relatively long time (of the order of a few seconds) for responding to the incident light.

A Photo-resistor. or LDR. Image source: © Nevit Dilmen, LDR 1480405 6 7 HDR Enhancer 1CC BY-SA 3.0
Object colourReflected light
 RedGreenBlue
Red  
Yellow 
Green  
Blue  
White
Black   
Table showing Red – Green – blue or RGB color composition. The ratio of the RGB light varies depending on the color of the object.

Where are color sensors used?

Color sensors have a range of applications in our day-to-day lives. Color sensors are used in:

  • Medical equipment: These devices are widely utilized in the field of medicine.
  • Industrial process control: Color detectors are used in several industrial machines and printers for manufacturing correction and inspection purposes.
  • RGB LED consistency control: Color detectors are used for analyzing the wavelength output of LEDs and other light types.
  • Light color temperature measurement: color detectors are used for measuring light color temperature that is necessary for designing lighting systems.
  • Security systems: Certain security systems also use color sensors for better results.

What are the color sensors available in the market?

Some popular color sensors readily available in the market are:

  • TCS3200
  • ColorPAL from parallax
  • SEN-11195
  •  TCS3200
  • TCS3400
  • TCS34715
  • TCS34727
  • Lego Mindstorms EV3

Apart from these, color sensors can be made by using Arduino.

To know more about optical sensors visit here.

About Sanchari Chakraborty

I am an eager learner, currently invested in the field of Applied Optics and Photonics. I am also an active member of SPIE (International society for optics and photonics) and OSI(Optical Society of India). My articles are aimed towards bringing quality science research topics to light in a simple yet informative way. Science has been evolving since time immemorial. So, I try my bit to tap into the evolution and present it to the readers.

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