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.

1. 1. 1. **1. 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):** It is categorized into several forms:

   *   **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.

1. 1. 1. **2. 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*), which is composed primarily of *Tejas* particles, allowing it to specifically perceive **colour and form** (*Rupa*).

1. 1. 1. **3. 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 ancient calculation yields approximately **299,000,000 meters per second** (or ~185,016 miles per second), which is 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 early philosophers like Cakrapani suggested that light travels much faster than sound, though both move in waves.

1. 1. 1. **4. 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 a **conical dispersion**.
• **Reflection and Refraction:**

   *   **Reflection** was explained as light rays striking a surface (like a mirror) and **rebounding** back to the observer.
   *   **Refraction** was understood as a **deflection** or change in velocity as light moves through different media, such as when it penetrates porous bodies or water.

• **Scattering (The Raman Effect):** Modern Indian contribution includes **C.V. Raman’s** discovery that the blue color of the sea is caused by the **scattering effect of sunlight**.
• **Particle Duality:** While modern science uses photons, ancient **Mimamsakas** also imagined light as minute **particles in constant motion** spreading through radiation and diffusion.

1. 1. 1. **5. The Spectrum and Colors**

• **Seven Colors:** The Rig Veda poetically refers to the Sun's chariot being drawn by **seven horses**, which is interpreted as the light being composed of **seven rays** or colors. These correspond to red, orange, yellow, green, blue, indigo, and violet.
• **Spectral Analysis:** Maharshi Bhardwaj’s work, *Amsubodhini*, describes instruments to measure the spectra in three regions: **Infrared** (*Gudhatam*), **Visible** (*Tam*), and **Ultraviolet** (*Andhatam*).
• **Advanced Materials:** The same work describes a material called ***Prakash Stambhanabhid Lauha***, which was engineered to be **transparent to infrared** radiation but **opaque to visible light**.

1. 1. 1. **6. Philosophical and Symbolic Meaning**

• **Light as Knowledge:** In Hindu tradition, light is a primary symbol for **Jnana (knowledge)** and **Prakasha (illumination of consciousness)**, used to dispel 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.