A world of colours by adding or subtracting

Light is the portion of radiation (electromagnetic waves) the eye can perceive. Wavelengths of light range from about 400 nanometers at the violet end of the spectrum to 700 nanometers at the red end: the rainbow.




The analysis of the interaction of light and matter concerns about the physics of colour. 

Light is the portion of radiation (electromagnetic waves) the eye can perceive.

Wavelengths of light range from about 400 nanometers at the violet end of the spectrum to 700 nanometers at the red end.

At shorter wavelengths, the electromagnetic spectrum extends to the ultraviolet radiation region and continues through X-rays and gamma rays. Just beyond the red end of the spectrum are the longer wave infrared radiation rays (which can be felt as heat), microwaves, smartphones and radio waves.




The sunlight, or artificial lamp that replicates the same light energy, is white, contains all the electromagnetic waves of the visible.

The materials when illuminated interact at the atomic and nanometric level.

They will appear black, if they absorb completely every radiation, they will be transparent, if they do not absorb all, if they absorb a part, the remaining one reflected (or transmitted) will appear colored.




The chromatic vision is related to the absorption of light by the three types of sensory organs present in the retina of the eye, named cones: cones L  catch mainly Red (R), cones M for Green (G) and cones S for Blue (B).

The three types of cones react to the light stimulus, proportionally to the intensity of the different light wavelengths.




In 1856 Hermann Grassmann discovered that is possible to reproduce any colour sensation perceived by the eye by overlapping three primary colours of suitable light intensities Red (Red), Green (Green) and Blue (Blue).

In fact, a light perceived as having a certain colour (e.g. yellow) can actually correspond to a monochromatic light at a precise wavelength (e.g. yellow ray at 575 nm) or to an overlap (mixture) of different chromatic rays (e.g. green ray at 520 nm + red ray at 700 nm).

Grassmann elaborated three laws and a model for colours studying. Two schools of colorimetry have been developed with the passing of time: the additive synthesis (RGB), used in the electronics sector and the subtractive synthesis (CMY), used in the pigments and inks sector.




Screens and projectors are engineered using the additive logic. The primary colors are RGB, each coloured source consists of only one “monochromatic” component.

The three colored sources light are related to the eye cones (photoreceptor cells), and variation their intensity can generate the full range of colours.




The “subtractive” logic is used by artists, press printers and in paint varnish world. The pigments are filters that subtract a single “monochromatic” from the starting white light, living almost unchanged the other two reflected (or transmitted) lights.

For example, a yellow pigment absorbs mainly blue (B) leaving red-green (RG), while magenta absorbs green fraction (G) and red-blue (RB) will remain. Mixing primary magenta pigment and primary yellow pigment, G and B are subtracted, and only red R, remains, which is well known by all CMYK printers and painters.




The representation of colors can be achieved by modulating three primary colors, and each color can be reproduced by mixing a certain quantity of each of the selected primaries. This operation of reproducing a reference color is called “color matching”.

Today to facilitate color matching activities, and to increase the range of reproducible colors, more primary colors are used than the minimum three required. In screens with Sharp Aquos technology, they use four RGBY primary lights, and in colorimetric systems, for paints and varnishes, they use more than seven primaries.


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