Why use Infrared for Machine Vision Lighting?
There are many different reasons to use infrared (IR) light in machine vision applications. Essentially, IR lighting enables vision systems to work outside of the visible spectrum. Examples include systems where:
1. Visible light needs to be avoided
2. Material is opaque to visible light
IR Machine Vision Lighting where visible light must be avoided
An obvious example of the use of IR Machine Vision lighting is a non-industrial example; that of Automatic Number/ License Plate Recognition (ANPR/ ALPR). IR lighting is chosen in this application primarily because it is not visible to the human eye. Visible light in such an application would negatively impact drivers. Wavelength selection is critical in this application as the wavelength must remain invisible to the human eye, but also take into account the sensitivity of the camera and the reflective properties of the licence plates.
IR Machine Vision lighting where the material is opaque to visible light
There are a wide range of examples of materials that are opaque to visible light, but transmit IR light, such as dark glass, certain plastics and semiconductor materials. Because machine vision cameras are typically sensitive to IR light, these cameras can be used with IR machine vision lighting to detect faults in dark glass, micro cracks and occlusions in semiconductor materials etc.