If you want even lighting, you need several bits of information:
- ceiling height
- angle of spread on the lamp (flood, spot, in-between)
- max spread of the fixture
From those values, you can determine the circle of illumination at the floor. Then, determine the amount of lumens you want and determine if the fixture can handle that size bulb. Different kinds of bulbs will have different amounts of light, and different fixtures will have different max size bulbs it can support.
Some of the better lighting manufacturers have some decent tables and diagrams that show you what's available. But, a formula...no.