While professional lighting equipment is useful, it is often perfectly possible to shoot a short film indoors using just natural light. However, there are still a few guidelines to bear in mind.
The main tip is to work with the light available wherever possible. So this means using whatever electric lights are in situ and controlling natural light by using curtains or blinds.
Assess whether your filming location is too bright or too dark and if there is anything you can do to fix the problem. For example, a strong beam of light from a window can be reduced by partly closing curtains to allow in some light but not all.
If a room is too dark, consider bringing in some table lamps to help. These are particularly useful as you can position the light wherever you need it.
Standing your subject facing a source of light, such as a window, is a good way to ensure they are illuminated on screen. Try to avoid shooting against a bright background, for example with a window behind them, as this can cause problems with exposure.
So expensive, professional lighting equipment is sometimes unnecessary. It’s usually a case of assessing the lighting situation and being creative with how you turn it around to your advantage.