Introduction to the History of Light & Physics
Greek Philosophers:


Law of Reflection
"Hero's Law"

Reflection at New World Encyclopedia

Hero ("Heron") of Alexandria at Kotaku



This is the experiment known to Ptolemy,
only his lacked a motor to spin the colorwheel,
so his disc therefore turned gray.

additive synthesis
Time-Life Books

This example of "additive synthesis" demonstrates the eye's inability to "keep up" with rapid movement,
"blending" the colors together.

Additive Color Synthesis at

Ptolemy at University of Oregon


During the Middle Ages, succession to the Arab world the study of light:

early concept of light rays, reflected
Alhazen (Ibn al-Haytham) & his theory of projected
"points of vision" correctly surmises the concept of optical focus.

Alhazen at University of Oxford


Johannes Kepler - Preeminence of his optical - retinal theory:

Kepler's basic understanding eliminated much confusion

Theories of Vision at University of Florida

Kepler at and at University of St. Andrews

Activity of other Baroque era Scientists:






Cow's eye dissection, after Descartes




Snell's experiments with Refraction:

Snell's Law of Refraction

etching of the mathematician

Willebrord van Royen Snell at University of St. Andrews

Snell's Law of Refraction at The Physics Classroom



1802 - Tri-chromatic theory of retinal vision by Thomas Young.

diagram of Young's theory

The Eye has three types of color receptors, or cones;
Red, Green, Blue

Tri-Color Vision at Harvard University

The Young–Helmholtz Theory at Wikipedia

Thomas Young and the Wave Nature of Light at Open Mind




At the early 19th century, general confusion regarding the physical nature of light,
due to it's contradictory wavelike & particle-like nature,
persisted in educated circles.

Antiquated Aristotelian concepts are presented in Goethe's 1810 Theory of Colors,
although his observations with regard to color relationships were a predecessor to the psychology of color.

Goethe's Color Wheel

Goethe on the Psychology of Color and Emotion at Brain Pickings

Goethe’s "Theory of Colors": The Treatise That Inspired Kandinsky at Open Culture




Light possesses both particle-like & wave-like properties

Wave-Particle Duality at Georgia State University and Boston University



1865 - Hermann von Helmholz elaborated on Young's theory with the introduction of the
"overlapping color sensitivity"
of the light receptors -
now the Young-Helmholz Theory of retinal vision.

photograph of the scientist  

Von Helmholz at Stanford University

The Ophthalmoscope in the Lifetime of Hermann von Helmholtz - Journal of the American Medical Association


General discussion of the Retina and Vision:
Rods & Cones at the Rochester Institute of Technology
The Photoelectric Effect at Arizona State University


lecture contents