In many houses, Akhanda Deepa (Nanda Deepa) is kept burning during the whole period.
In some houses it is kept for the concluding three days from Saptami(without any break).
This Deepa is to be kept burning all the 24 hours from the moment it is lighted, (with pure ghee or pure til-oil).
Akhandha Deepa is a symbol of Lord Srinivasa. Hence it should be lighted with Madi, maximum practicable in the house.
Deepa-Paatra is a sacred thing because it is a seat for Srinivasa. All the light-giving Devatas stand in service to Lord.
With this thought, decorate the Deepa-Paatra with Pushpa, Arishina and KumKuma.
Fill it with ghee or oil, keep the wick (Bat-thi) in its place and keep it ready for lighting.
Now bring to your mind that at the top of the Deepa-Sthambha, Krittika and all the 27 Nakshatra Devatas are present. In the wick (Naala), Vaasuki Devata is present. At the foot of the Deepa-Sthamba, Chandra and Soorya are present.
Then, light the usual Mangalarathi-Bathi in Devara-Deepa by singing any appropriate DevaraNama and lit the Akhanda deepa with the Mangalaarati flame.
Now the Lord Srinivasa from the seven Hills, has arrived in the house to protect the entire family.
The lady of the house, is the custodian of Deepas.
Akhanda Deepa should burn day & night during Nava-ratri.
Two-time Pooja during the Navaratri is a MUST; be it grand or simple
If Akhanda Deepa needs kindling and relighting, minimum Madi should be observed. It should not be touched casually with impure clothing. Change the clothing and then touch.
This Dipa should not be lighted with match-sticks. Light another Dipa with match-sticks and from that lamp, take the flame for Akhanda Dipa, using Tulasi Kaashta or Bathi.