Optics and Acoustics

Light as a topic is dealt with in Optics and sound in Acoustics. Light Information regarding light across these sources encompasses its encompasses its classification as a fundamental element, its role in the mechanism of vision, detailed calculations of its speed, and advanced physical behaviors such as reflection, refraction, and spectral analysis.

Nature and Elemental Classification

• The Element Tejas: Light is fundamentally identified with Tejas (fire), one of the five Panchamahabhutas. It is described as a substance that destroys darkness (Tamas) and is characterized by a brilliant white colour (Bhaswara Shukla) and hot touch (Ushna Sparsha).

• Origin: In ancient texts like the Taittirīya Upaniṣad, Tejas is said to be born out of the friction of Vayu (air/motion).

• Types of Light (Tejas):

 ** Bhouma – Earthly fire (e.g., burning wood)
 ** Divya – Heavenly light, such as the Sun, stars, and lightning
 ** Audarya – Stomachic fire (metabolic energy for digestion)
 ** Akaraja – The luster or brightness of minerals like gold and silver

Theories of Vision and Perception

• Evolution of Vision Theory: Early Indian philosophical systems hypothesized that light rays emanated from the eyes to touch objects, similar to a candle casting light.

• Susruta’s Correction:' This view was corrected around the 1st Century CE by Susruta, who posited that light arriving from an external source hits the retina to illuminate the world—a view later supported by Aryabhata in the 5th Century.

• Visual Sense Organ: The eye is considered the seat of the visual sense organ (Caksurindriya), composed primarily of Tejas particles, allowing it to specifically perceive colour and form (Rupa).

The Speed of Light

• Vedic Calculations: A renowned reference to the velocity of light is found in Sayana’s 14th-century commentary on Rig Veda 1.50.4.

• The Formula: The text states that the Sun’s light traverses 2,202 yojanas in half a nimisha.

• Modern Equivalence: When converted, this yields approximately 299,000,000 meters per second (or ~185,016 miles per second), remarkably close to the modern scientific value of 299,792,458 m/s.

• Relative Speed: The Surya Siddhanta notes that Sun’s rays travel ten times faster than the Moon’s, and philosophers like Cakrapani suggested that light travels much faster than sound.

Physical Behaviors and Optics

• Propagation: Sage Kanada in the Vaisheshika Sutra stated that light particles are extremely subtle and move in straight paths. They are described as indefinitely small particles radiating with conical dispersion.

• Reflection: Light rays striking a surface (such as a mirror) rebound back to the observer.

• Refraction: Light was understood as undergoing deflection or change in velocity when moving through different media, such as water or porous bodies.

• Scattering (Modern Contribution): C. V. Raman explained that the blue color of the sea is caused by the scattering of sunlight.

• Particle Concept: Ancient Mimamsakas also imagined light as minute particles in constant motion spreading through radiation and diffusion.

The Spectrum and Colors

• Seven Colors: The Rig Veda poetically refers to the Sun's chariot being drawn by seven horses, interpreted as seven rays or colors:

 ** Red
 ** Orange
 ** Yellow
 ** Green
 ** Blue
 ** Indigo
 ** Violet

• Spectral Analysis: Maharshi Bhardwaj in Amsubodhini described instruments to measure spectra in three regions:

 ** Gudhatam – Infrared
 ** Tam – Visible
 ** Andhatam – Ultraviolet

• Advanced Materials: The same work describes a material called Prakash Stambhanabhid Lauha engineered to be transparent to infrared radiation but opaque to visible light.

Philosophical and Symbolic Meaning

• Light as Knowledge: In Hindu tradition, light symbolizes Jnana (knowledge) and Prakasha (illumination of consciousness), dispelling the darkness of ignorance.

• Jyotish: The word Jyotish (Vedic astronomy/astrology) literally means light, referring to the science that sheds light on the mysteries of the universe.