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Light as a topic is dealt with in Optics and sound in Acoustics. Visual and auditory senses play an important role as primary carriers of information. Indian shastras referred to light as prakasa, tejas. Indian texts encompass 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. Ear recognizes sound related to the Akasha element. Remarkably modern and ancient Indian theory regarding the origin and propagation of sound are largely aligned.  

Light as a topic is dealt with in Optics and sound in Acoustics. Visual and auditory senses play an important role as primary carriers of information. Indian shastras referred to light as prakasa, tejas. Indian texts encompass 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. Ear recognizes sound related to the Akasha element. Remarkably modern and ancient Indian theory regarding the origin and propagation of sound are largely aligned.  

== Introduction ==

== परिचयः ॥ Introduction ==

Indian texts offer a large number of principles and concepts regarding light and sound. Yogasutras present Nada, the primordial sound, as fundamental to the understanding of consciousness and the material world.  Nada is conceptualized both as the physical vibration and a metaphysical essence for the origin of creation.  

Shastras offer a large number of principles and concepts regarding light and sound. Yogasutras present Nada, the primordial sound, as fundamental to the understanding of consciousness and the material world.  Nada is conceptualized both as the physical vibration and a metaphysical essence for the origin of creation.  

Light in Indian tradition is not merely physical illumination but enables perception and cognition. Indian concept of light just like sound, transcends simple optical physics, and encompasses both physical and metaphysical aspects. Epistemically light is that which both exists and reveals existence.  

Light in Indian tradition is not merely physical illumination but enables perception and cognition. Indian concept of light just like sound, transcends simple optical physics, and encompasses both physical and metaphysical aspects. Epistemically light is that which both exists and reveals existence.  

Temple architecture embodies the very principles of resonance, illumination and even musical notes.

Temple architecture embodies the very principles of resonance, illumination and even musical notes.

== Nature and Elemental Classification ==

== Light ==

* '''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'').

* '''The Element Tejas and its attributes:''' Light is fundamentally identified with '''Tejas''' (fire),<ref name=":0">Vijnana Bharati. (2019). ''INDIAN CONTRIBUTIONS TO SCIENCE'' (Fourth). (p.326)</ref> one of the five [[Panchamahabhutas (पञ्चमहाभूतानि)|Panchamahabhutas]]. It is described as a substance that destroys darkness (''Tamas''). Tejas refers to radiance or brilliance and is associated with the concept of [[Agni (अग्निः)|Agni]], a form of energy that fills the universe. Agni has the gunas of rupa and sparsa as mentioned in Ayurvedic and Vaiseshika texts. तेजो रूपस्पर्शवत् । २,१.३ । tejo rūpasparśavat | 2,1.3 | (Vais. Sutr. 2.1.3)<ref>[https://sa.wikisource.org/wiki/%E0%A4%B5%E0%A5%88%E0%A4%B6%E0%A5%87%E0%A4%B7%E0%A4%BF%E0%A4%95%E0%A4%B8%E0%A5%82%E0%A4%A4%E0%A5%8D%E0%A4%B0%E0%A4%AE%E0%A5%8D_(%E0%A4%95%E0%A4%A3%E0%A4%BE%E0%A4%A6%E0%A4%83) Vaiseshika Sutras of Kanada]</ref> It is characterized by a brilliant white colour (''Bhaswara Shukla'') and hot touch (''Ushna Sparsha'').<ref name=":1">Narasimhacharyulu, K.V.L (2010) 4th ed. ''[https://www.sacpilani.org/Books/Padartha%20Vijnana.pdf Padartha Vijnana]'', Varanasi: Chaukhamba Krishnadas Academy (Chapter 2, 36-109)</ref> It denotes not only the physical fire but also the concepts of tapas or spiritual discipline, the source of inner strength and illumination. [[Agni in Ayurveda (आयुर्वेदे अग्निः)|Agni in Ayurveda]] has a pivotal role in nature as well as in human beings.<ref name=":1" />

* '''Origin:''' In the ''Taittirīya Upaniṣad'', ''Tejas'' is said to be born out of the friction of '''Vayu''' (air/motion).

* '''Origin:''' In the ''Taittirīya Upaniṣad'', ''Tejas'' is said to be born out of the friction of '''Vayu''' (air/motion). वायोरग्निः । vāyoragniḥ | (Tait. Upan. 2.1.1)<ref>Taittriya Upanishad ([https://sa.wikisource.org/wiki/%E0%A4%A4%E0%A5%88%E0%A4%A4%E0%A5%8D%E0%A4%A4%E0%A4%BF%E0%A4%B0%E0%A5%80%E0%A4%AF%E0%A5%8B%E0%A4%AA%E0%A4%A8%E0%A4%BF%E0%A4%B7%E0%A4%A6%E0%A4%A4%E0%A5%8D/%E0%A4%AC%E0%A5%8D%E0%A4%B0%E0%A4%B9%E0%A5%8D%E0%A4%AE%E0%A4%BE%E0%A4%A8%E0%A4%A8%E0%A5%8D%E0%A4%A6%E0%A4%B5%E0%A4%B2%E0%A5%8D%E0%A4%B2%E0%A5%80 Brahmananda valli Anuvaka 1])</ref> Sparsha tanmatra is required for the formation of Agni and it is present in Vayu. Friction takes place when Vayu is in motion and any obstruction in the movement of Vayu gives rise to Agni. It agrees well with modern concept of friction generating heat and light.<ref name=":1" />

* '''Types of Light (Tejas):'''

* '''तेजो भेदाः ॥ Types of Light (Tejas):''' Tejo bhuta is classified as Nitya and Anitya. Nitya tejas is in the paramanu Rupa. Anitya tejas is again classified as<ref name=":1" />

  ** '''Bhouma''' – Earthly fire (e.g., burning wood)

*# Sarira sanjnaka: These include the glittering grahas (planets), nakshatras, and other bodies in the planetary system which are flaming masses of molten viscous matters

  ** '''Divya''' – Heavenly light, such as the Sun, stars, and lightning

*# Indriya sanjnaka: This includes chakshurindriya, the eye which perceives the knowledge of the attribute Rupa or form of tejas.

  ** '''Audarya''' – Stomachic fire (metabolic energy for digestion)

  ** '''Akaraja''' – The luster or brightness of minerals like gold and silver

'''1. भौमः ॥  Bhouma or Bhoutikagni''' – Earthly fire arising with the help of fuel (e.g., burning wood or oil-lamp) includes a chemical union with Prthvi bhuta particles acted upon by energy releasing the latent Tejas particles of light and heat as flame.

'''2. दिव्यः ॥ Divya''' – It includes the light of the sun and stars which are flaming masses of molten viscous matters or of earthly matter. Then there is lightning which liberates a kind of Tejas due to water particles and vapours under the action of energy.

'''3. औदार्य ॥ Audarya''' – Animal heat due to the digestive fire in the living beings which processes food, also called Jatharagni (metabolic energy for digestion) comes under this category.

'''4. आकरजम् ॥ Akaraja''' – It is a peculiar form of the Tejas energy (radiant energy) stored in the metallic and ferrous ores and igneous rocks. It radiates as luster or brightness of minerals like gold and silver and others coming out from the mines.

== Theories of Vision and Perception ==

=== Theories of Vision and Perception ===

'''Susruta’s Correction:'<nowiki/>'' This view was corrected around the 1st Century CE by '''''<nowiki/>''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.

 

* '''Susruta’s Correction:'<nowiki/>'' This view was corrected around the 1st Century CE by '''''<nowiki/>''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'').

 

* '''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 ==

== The Speed of Light ==