Artificial Light comes from Natural Light

Light has become one of the most interesting phenomena across the planet Earth history. The Sun, has been emitting radiation to the Earth since approx. 6.000.000.000 years, thanks to the combination of two components, helium and hydrogen, that we can find in his nucleus and his atmosphere. Each second, 654.600.000 tons of hydrogen fuses into 650.000.000 tons of helium in the external layer of the nucleus. The small quantity of energy of this fusion arriving to the Earth surface is enough to maintain the whole life in our planet. 

NASA Sun storm pictures

Due to the huge quantity of these two elements, we can say that this star has been emitting radiation only for a while. What will happen when these reserves will become exhausted? It is thought that when the hydrogen reserves will exhaust, the helium nucleus will grow and will start his fusion, converting the star in a red and giant entity emitting intense heat. This will cause the seas evaporation and consequently the end of life known up to now.  But no worries at all… still at least 8.000.000.000 millions of years to enter in this second phase. 

Nasa Sun storm pictures

Therefore, the Sun has become the catalyst element for life. Plants receive radiation from the sun and realize photosynthesis (Carbon Dioxide + Sun Radiation + H2O = O2 + sucrose), herbivores absorb a small quantity of this energy eating this plants, and carnivores absorb a smaller quantity eating herbivores.

Plant Cells

Equally, don’t forget that the great majority of human energy sources are based in the energy emitted by the sun. Fossil fuel preserve the energy captured millions of years ago, hydroelectric energy uses the potential energy of water through the hydrologic cycle that passes by the three physical matters (oceanic water evaporation, condensation, precipitation and run-off). Eolic energy is another way of radiation profiting;  winds are originated when the Sun heats with different intensity some Earth areas. Solar cells are of course, one of the best systems to transform solar radiation into electrical power using semiconductors that exhibit the photovoltaic effect; this refers to photons of light exciting electrons into higher state of energy, allowing them to act as charge carriers for an electric current. 

In this way, Photons, an elementary particle, the quantum of light and all other forms of electromagnetic radiation and the force carrier for the electromagnetic force, according to his energy or wavelength are capable of: photo-ionize the external layer of an atom, excite atom electrons to another upper layer, dissociate a molecule, vibrate molecules and rotate molecules. There are so many natural processes where light has an active paper.

Radiations are visible when are inscribed in wavelengths between approximately 380 mµ and 780 mµ. That means human eye is reactive to this set of wavelengths, but all values above 780 mµ is Infrared non-visible light  and all under 380 mµ is Ultraviolet and is also non-visible for the human eye.

Regarding the first article appeared in this blog “Light Vs Pigment”, and putting the question what was before for the first human eye (light colours or pigment colours?) it is now clear that colour pigments in object surfaces are possible because lighting existence. Our retina only is capable to see specific wavelengths in radiation, and one of the biggest features is colour. For the human eye, not only all the visible wavelengths generates the same sensitivity. This is why Matthew Luckiesh (1916). In his book “Light and shade and their applications”. (D. Van Nostrand Company), he started to define the “Spectral sensitivity curves of human cone cells". His study revealed that the most sensitivity radiation belongs to wavelengths close to 550 mµ, which corresponds to yellow and green colours. (see graphic below)

Despite its multiple accepted meanings the first definition of light in the Oxford dictionary is:

 “Noun 1 [mass noun] the natural agent that stimulates sight and makes things visible”

But another definition more in relationship with physics is when its referred to “visible light” as we can see in the CIE (1987). International Lighting Vocabulary. Number 17.4. CIE, 4th edition. ISBN 978-3-900734-07-7.By the International Lighting Vocabulary, the definition of light is: 

“Any radiation capable of causing a visual sensation directly.”

I will highlight the fact that light is considerated from a human point of view, because all definitions are in relationship with our capability to see specific wavelenghts of this radiation, and are always connected to the fact that we need physical objects around us to reflect this light. If not there’s no sense about its meaning.

In an empty world without any object reflecting this radiation, the term "light" become completely senseless for us.

The sun is the father of light in all its extension. In our contemporary world, we are not able not create artifical light without the existence of solar radiation. It's an essencial element that serves as a base life and to develop our own systems to replace or complement the natural lighting with the artificial ones...