How to calculate the heat produced by lights in data center? What are the formula used?

Answer 1

BTU=(Total lighting power in Watts)x3.413(BTU/Watt)
Take the total power load of the lighting system in Watts
(Be sure to include any power used by ballast or transformers)
For a ball park answer just multiply Watts by 3.5
That will get you close with a safety margin.

Is the data center manned or unmanned?
If no one is there the lights don’t need to be on.
I like to design low level lights for folks just passing through. (Also helps you see when alarm lights or no lights are on the equipment.)
Then have higher level work lights, even movable spot lights, for working inside of the racks.

You might want to look at LED lighting. The lower power use and thermal load could reduce the operating cost enough to cover the price tag.

Answer 2

# of bulbs * wattage of each bulb = Qdot due to lighting.