For the most part of the history of mankind, from the origins of man up to the 18. Century, there were basically two sources of light available.
The older one of these two is daylight, the medium by which we see and to whose properties the eye has adapted over millions of years.
A considerable time elapsed before the stone age, with its development of cultural techniques and tools, added the flame as a second,
artificial light source. From this time on lighting conditions remained the same for a considerable time.
Lighting was limited to daylight and flame and it was for this very reason that man has continued to perfect
the application of these two light sources for tens of thousands of years.