Know this: Why we light a Lamp?

Light symbolizes knowledge, whereas darkness, ignorance. The Lord is the "Knowledge Principle" (chaitanya चैतन्य) who is the source, the enlivener and the illuminator of all knowledge. Hence light is worshiped as the Lord himself.

Knowledge removes ignorance just as light removes darkness. Also knowledge is a lasting inner wealth by which all outer achievement can be accomplished.

Hence we light the lamp to bow down to knowledge as the greatest of all forms of wealth. In many Indian homes, a lamp is lit daily before the altar of the Lord. In some houses it is lit at dawn, in some, twice a day – at dawn and dusk – and in a few it is maintained continuously (akhanda deepa). All auspicious functions commence with the lighting of the lamp, which is often maintained right through the occasion.

 Why not light a bulb or tube light? That too would remove darkness. But the traditional oil lamp has a further spiritual significance. The oil or ghee in the lamp symbolizes our vaasanas or negative tendencies and the wick, the ego. When lit by spiritual knowledge, the vaasanas get slowly exhausted and the ego too finally perishes. The flame of a lamp always burns upwards. Similarly we should acquire such knowledge as to take us towards higher ideals.

Whilst lighting the lamp we thus pray:

दीपो ज्योति परं ब्रह्म दीपो ज्योतिर्जनार्दन: ದೀಪೋ ಜ್ಯೋತಿ ಪರಂ ಬ್ರಹ್ಮ ಡೀಪ್ ಜ್ಯೋತಿರ್ಜನಾರ್ದನ್ . Deepo jyoti parm brahm deepo jyotirjanardanh,

दीपो हरतु ये पापं संध्यादीप नमोस्तुते // ದೀಪೋ ಹರುತ್ ಏ ಪಾಪಂ ಸಂಧ್ಯದೀಪ್ ನಮೋಸ್ತುತೆ. Deepo haratu ye papm sandhyadeep namostute.

शुभं  करोति कल्याणम  आरोग्यं सुखसम्प्दाम  ಶುಭಂ ಕರೋತಿ ಕಲ್ಯಾಣಂ ಆರೋಗ್ಯಂ ಸುಖಸಂಪ್ದಾಂ Shubhm karoti kalyanm aarogym sukhsampdam,

मम बुद्धिप्रकाशस्च  दीप्ज्योतिर्नमोअस्तु ते //  ಮಮ ಬುದ್ಧಿಪ್ರಕಶಚ್  ದೀಪ್ಜ್ಯೋತಿರ್ನಮೊಅಸ್ತು ತೆ. Mam buddhiprakashach deepjyotirnamoastu te..

I prostrate to the dawn/dusk lamp; whose light is the Knowledge Principle (the Supreme Lord) the brahma and the vishnu, removes all my sins. I also prostate to the flame of lamp, whose light brings happiness, wealth and well being and also enlightens my intellegence.

Compilation from various sources... (error in translation if any is regretted.)