How many lumen's needed for good indoor photography?

Answer 1

If you are familiar enough with the word, you must also know that a lumen is a quantitative measure of light contained in a defined beam or emitted from a source, and depends upon the spectrum of the light.

Since virtually every photographic image ever made or that will be made in the genre you refer to ("indoor Photography)

a) depends on reflected light

b) the spectrum will vary from daylight, tungsten and fluorescent to name a few

c) the reflective surfaces absorb and colorize the light

d) the amount transmitted to the film or ccd depends on aperture and shutter speed

e) the amount of light required depends on the film speed rating

your question is purely academic. Even if you wish to use an incident light meter that indicates the lumens falling onto the scene, you will no doubt concentrate on the aperture and shutter speeds indicated as a function of the film speed and not care a whit about how many lumens are present.