Maa Durga is considered to be the devatha for Ragu. Hence, this practice of lighting lemon lamps to maa durga during rahu kalam is considered auspicious to get rid of the bad effects of rahu. Predominantly, this is done during rahu kalam on Tuesdays and Thursdays. Basically, a lemon can be cut and the juice be squeezed. The resulting two outer covering can be turned upside down and lit as two lamps. This is practiced throughout the year and not specific to any month.
Durga Matha who is also called as ThurithaNivarini/ Thukkanivarini which means immediately she solve all our problems. Auspicious days for Devi Durga are tuesday (3.00 pm to 4.30 pm) and friday (10.30 am to 12.00 pm) and the day for Rahu Bhagvan is sunday (4.30 pm to 6.00 pm). There are lot of procedures which vary from one another. But the common is light with the lemon.
Pair lemon diyas should be filled with ghee and light it. Decor diya with flower and Tilak with turmeric and Kumkum. To cool down Matha we provide lemon and make her happy and she fulfill all our desires. In somewhere they make the juice as a Paanagam ( Make with jaggery) and after pray the god they give the juice who are in the temple as Prasadam.