• The hypothesis accepted until now was based in the fact that radiation from the Sun has its maximum intensity near the absorption peaks of human vision• This study uses information theory and the entropy of radiation to explain why human vision has evolved to adapt to solar radiation

Newswise — Although the human eye is capable of seen in all the colours (the whole radiation visible spectra), there are two colours -two wavelengths- at which the vision is better, depending on the illumination. Hence, at bright light, Photopic vision has its maximum in 555 nanometres (nm), and at low light illumination conditions, such as sunset or indoors, Scotopic vision has its maximum at 507 nm.

So far, the most spread hypothesis among scientists to explain those values was that radiation from the Sun has its maximum near those values. The maximum intensity wavelength is determined with the Wien’s law, which depends only on the temperature of the Sun.

However, a new study suggests that human vision absorption peaks do not only depend on the energy of radiation but also on its entropy, a thermodynamic magnitude related with the information obtained from the environment.

Not all the wavelengths contain the same entropy (information), and human vision has adapted to those which provide the best amount of energy and information. This research, published in Scientific Reports, offers a new way to explain why human vision has evolved to adapt to those particular wavelengths and no others.

“The wavelength of maximum radiation of our Sun is around 499 nm, which is not exactly the Scotopic absorption peak (507 nm). When radiation passes thought the atmosphere, the maximum is moved to approximately 547 nm, a value which does not match the Photopic peak either (555 nm)”, explains Delgado-Bonal, first author of the research paper. “But when the two variables -energy and entropy- are taken into account, the human absorption peaks match exactly the optimal wavelengths for the obtaining of information”.

Analysing the entropy of radiation, a variable which is usually overlooked, a new Wien’s like law for the entropy is found with a constant (bentropy) which cannot be obtained from the energy (benergy). Combining these maxima, the research paper provides an explanation of why human beings have adapted to those absorption peaks: it is not the most energetic situation, nor the most entropic, but it contains the best balance between energy and information.

The research has been developed following theoretical and numerical techniques, and it offers new ways to analyse processes in telecommunications, ecology or solar energy conversion, and in general in any system involving information transfer by radiation.

Cite as:A. Delgado-Bonal and J. Martin-Torres, Human vision is determined based on information theory. Scientific Reports 6., 36038. http://dx.doi.org/10.1038/srep36038