Lighting

Color Considerations

Wavelength and Color

Most IMAC products can be characterized by the wavelengths shown above, ultraviolet through visible to infrared. The visible light spectrum can be seen by the human eye ranging from approximately 380nm to 750nm.

Historically, red LED lights were the most commonly used due to cost and availability. At the same time, cameras were more sensitive to red wavelengths.

Use Complementary and Similar Colors to Create Contrast

High contrast images depend on appropriate use of complementary and similar colors. Use light from the same or similar spectrum to make a part feature appear bright. Use light from the opposite or complementary spectrum to make a part feature appear dark. A red light will make a red feature appear bright, and a green light will make the same feature appear dark.

Examples:

• If you wish to make the yellow fish appear dark, use a blue light, rather than a red or green light.

• If you wish to make the magenta octopus appear bright, use a red light, rather than a green light.

When light strikes an object:

the light could be reflected by the object,

the light could be transmitted through the object,

the light could be absorbed by the object, or

the light could be absorbed, triggering emission of light of a different wavelength, i.e. fluorescence.

Energy that is absorbed will never be seen by the camera or sensor, thus the feature appears dark.

Wavelength and Scattering Rate

In addition to complementary and similar colors, scattering rate also affects image contrast. Scattering rate refers to the tendency of light rays to be reflected in different directions from the surface of a part. Scattering rate is inversely proportional to wavelength, ie. the shorter the wavelength, the higher the scattering rate. Light with a high scattering rate is effective for surface inspection.

Example:

The shorter wavelength and higher scattering rate of a blue light results in more apparent surface defects than that of a red light.