How much light does a window let in?

Let's assume we have a room with 20m². Now we plan a window with 2m² glass area for this room. How bright is that?

How bright is the room with 10m² glass area?

From how many m² of window will the room hardly get any brighter?

etc.

Is there a rule of thumb to find this out or maybe even a calculator or a small formula to determine this?

Maybe even with external influences such as a nearby tree, carport, neighboring house, overlying balcony, orientation of the window to North/East/South/West

In my opinion, that depends on many factors, e.g. direction and sunlight.

Hello, yes that is true. But somehow you have to be able to predict whether enough windows will be installed for brightness x or how it looks with the planned [Inhalte in eckigen Klammern dürfen nicht übersetzt werden].

The state building regulations say that in BW, about 1/10 of the room area must be window area.

The TL value then tells you how much light passes through the pane.

Now you can theoretically plan 20m2 of window area, so you have TL70% light transmission.
But you never need that much, or do you not want to place any furniture?

Hello Tom, the thing with the room was just written by me as a thought experiment ;)

What is the tl value and how are the 70% determined? How much is needed for a bright room? And what is generally defined as bright?

I once read that an office room must have 500 lux (regardless of whether daylight or artificial light) and a workplace with small electronic components must have 800 or 1000 lux.

Accordingly, I would say, without being able to properly assess it now, that 1000 lux can be considered bright.

The tl value is the value of how much sunlight passes through and it is indicated on your window.

I also cannot answer the question for you, only that too much window area without shading in summer overheats the house too much.
So blinds or roller shutters are mandatory.