In India, the entire household lights the lamp in front of the GOD (He may be in the shape of photograph, statue, painting, etc. The timings may differ – Somewhere at Dawn, Somewhere at Dusk, somewhere both the times. Somewhere continuously (You may notice these in the popular temples and popular persons memorial). And also during any occasion, the ritual is that the function starts with lighting a lamp by the chief guest. And the lamp is giving light throughout the function.
Why lamp? How it helps?
First of all, in ancient days when there were no electricity and it was jungle everywhere, the people started this as an essential requirement to see each other and to establish that there is a meeting taking place.
If you consider it in the philosophical terms:
The lamp symbolizes: The knowledge. The knowledge removes/replaces the ignorance – light replaces the darkness.
Why the tube lights and modern day bulbs are not used in worshipping. I do not know.
But the lamp with oil or ghee as a medium gives us the aroma and they are not warming the globe. Our forefathers would have thought well in advance about our ill treatment to the mother earth.