The emitters in photoelectric sensors give off a light that is received by a separate receiver, reflected back to a receiver by a reflector, or reflected back by the object itself. Back in the good ‘ol days, the light source was incandescent, however they ran hot and tended to have a short life. Now solid state devices, LED’s, are used because they use less energy, they can be pulsed very rapidly and you can use different colors for special applications.
Typically we refer to light sources in photoelectrics as red light, infrared, and laser. All have their advantages and disadvantages, and picking the wrong light source, can either make your application successful, or let’s say less desirable than you had hoped.
Red light photos are probably the most favored because they are easy to set-up, and confirmation that the sensor is working properly is easy since you have a bright light that you can focus on your target. However, it is important that you aim the sensor correctly if you have the sensor installed near an operator as the light can be rather annoying if it is in their eyes.
Recently laser photoelectric sensors have become more popular. Unfortunately, many think that since they are laser they are the most powerful light sources available. Lasers obviously are visible which aids in setup and alignment. They provide a consistent wavelength or color and best of all a small light beam diameter that is perfect for small part detection and precise measuring. One of the disadvantages of lasers is that they are more costly than standard red light sensors. If you are using a laser for measuring make sure your light beam is larger than any pits or crevasses in your part to insure your measurement is as accurate as possible. If you decide to use a laser insure that they are installed so that the laser is not aimed into an operator or passerby’s eyes.
A lot folks think that lasers provide the most power for a photoelectric sensor however, they do not. Although the light beam is small and concentrated, they can be easily interrupted by airborne particles. So, if there is dust or mist in your environment the light will be scattered making your application less successful than desired. Infrared LED’s provide the most power with the least amount of heat and is the most efficient light source and provides some of the longest ranges. Infrared light sources are perfect for harsh and contaminated environments where there is oil or dust. However, with the good comes the bad. Since the light source is infrared and not visible setup and alignment can be challenging.
So, which light source do I use? The answer is…it depends on your application, environment, target and so forth. Once you have decided on your light source be sure to test it for the most successful results.