Color of light

First of all, it is important to note that there are two different color systems: The 'additive' and the 'subtractive' system. It is termed subtractive the system which, combining all three pigment colors, the result is a dark color almost black. This system is typical of printed colors, inks, etc. On the other hand, the additive is that system in which, combining all primary colors (RGB), the result is a light colour or white, characteristic of focus and screens, etc. Light is additive and overlapping all colors results in white light.

There are many universal classifications of color spaces but, when referring to artificial vision, the main mode is the RGB, a mix of red, green and blue that constitutes the primary colors that are used by cameras, PCs and screens and, which in combination, can create almost any colour in the visible spectrum.

When light falls into an item, its surface absorbs some wavelengths and reflects other. The reflected wavelengths are those which the human eye captures and interprets as different colors, according to the correspondent wavelength. The white light is the overlapping of all colors of visible spectrum.

The colour cameras emulate the function of human eye by using a matrix composed of sensors which capture different ranges of the visible spectrum. Usually, they use three ranges, red (R), green (G) and blue (B). Later, they group in one pixel with three values Red-Green-Blue all information obtained by the sensor in each group (RGB).

For instance, based on RGB mode, a red object will absorb the green and blue light and will reflect the red light. A white object will reflect all colors.

Illumination for machine vision uses all this to its advantage in order to reveal certain characteristics about a particular object. The vision is then, the ability to detect light and interpret it.

Of the entire electromagnetic spectrum, the visible part to the human eye is very small and comprises wavelengths between 380nm and 760nm or so, although it may vary depending on the person.

Besides the visible spectrum, is important to consider the ultraviolet light and infrared light, because they can be useful for some other characteristics of the object of inspection. Cameras have a different spectral response than it has the human eye and therefore, they are sensitive to them.

The colour of light is one of the five factors affecting lighting and in DCM Sistemes is identified as follows:

Colour	Wavelength	Code	Availability	Light type
UV-	365nm	365	Standard	Monochromatic
UV	400nm	400	Standard	Monochromatic
Royal Blue	455nm	455	Custom *	Monochromatic
Blue	470nm	470	Standard	Monochromatic
Green	525nm	525	Standard	Monochromatic
Red	630nm	630	Standard	Monochromatic
Cherry Red	730nm	730	Custom *	Monochromatic
IR	850nm	850	Standard	Monochromatic
IR+	940nm	940	Custom *	Monochromatic
White	-	W00	Standard	White
RGB	-	RGB	Standard	RGB

* Wavelengths 455nm (indigo), 730nm (cherry) and 940 (infrared+) are available on demand for the ALB, AMS, AUB, DOL, DOM (only DOM5652B, DOM5652C, DOMB2B1A), PLA, PLC, PRA, PRC, PRF, PRH, PRK and PRL series.

For any other wavelength or combination, check availability here

As we can observe from the table above, we are able to group the light in monochromatic, white or RGB, according to the colour. Each of these three groups will contribute with different characteristics that we will have to take advantage of for inspecting the objects.

► Monochromatic light.

► White light.

► RGB light.