A Diya or Jyoti is a symbol of knowledge, purity, good luck, prosperity. In other words, it represents the absence of darkness/ignorance. And the lamp that remains ignited for several days is referred to as Akhand Jyoti. You may place the Akhand Jyoti in the centre of the Ashtadal.
This must be kept to the right of the Mother Goddess on the chowki or the altar. Use a long and thick Baati ( cotton wick) or the one made of Mauli to help it remain ignited until the end of the ninth day of the festival. A burning lamp keeps on emitting soot or unburnt activated carbon particles.
They work like charcoal, which is a purification agent. They absorb all the impurities and pathogens of the atmosphere on their surface and render them harmless. By lighting a lamp in front of your deity at home, you remind yourself that truth is where God is and light is where knowledge is. The wick used in the lamp represents our ego while the oil symbolises the impurities in our mind.