where can i shop for ceiling lights, chandelier lights in Guangzhou?

I know a big market near Zhujiang New Town which is called Nantian Lighting City and I suggest you to have a try there. The address is No. 1, Huacheng Road, Zhujiang New Town.
For the trade fair, do you mean the Canton Fair. If so, there are two times of the exihibition every year, April, 15th to May 5th and from Oct. 15th to November, 4th.
Besides, you can find many lighting markets in Canton, you can pick up one near your hotel.