ᐅ How many light fixtures should be installed in a 7-meter-long hallway?

For a layperson, your post isn’t very helpful.
Who can really imagine what lumens or lux mean?
Usually, ceiling height doesn’t make much of a difference unless you have a clear height of 3.5 meters (11.5 feet). Whether it’s 2.5 meters (8.2 feet) or 2.7 meters (8.9 feet) is basically irrelevant.
Even if I say that 1 lux corresponds to the illumination from a candle about 1 meter (3.3 feet) away from a wall, that usually doesn’t help much...
If you want to know precisely and plan to design rather dark walls, you need to consult a lighting designer. Otherwise, visiting prefab house showrooms can give you a rough guideline.

What I actually want to say is: whether you plan 3 or 5 spotlights over 7 meters (23 feet) mainly matters for aesthetics or symmetry. The light fixtures themselves are what count, and at least I’ve experimented and tinkered quite a lot with them.

Googling usually helps in most cases, but it requires specific reference points – and 4000 K is really the least significant figure in this context. If links were allowed here, I would have provided some, but you’ll have to find examples yourself to understand how bright 100 lux is. Spoiler: There are plenty available.

You will also find plenty of tools for calculation, but either way, you inevitably have to engage with the subject yourself – or pay someone to do it and trust that they do it well.

I can report that I was allowed to visit a neighbor with an identical house. He has the two standard light points that are planned and no additional stair lighting. Unfortunately, the visit was during the day, so it wasn’t completely dark anyway. For him, the lighting was sufficient. I will plan to add one more light point. That should be enough.

Thank you for your answers. Some were too technical for me (since I’m a layperson). For now, it will stay as suggested by someone: between 2 and 4 light points.

That’s fine. Just make sure to refer back to this thread when selecting the lighting fixtures and take a closer look at the specifications of the options, such as luminous flux, beam angle, and so on.

Lighting is, in my opinion, always a matter of personal taste. Some prefer it brighter, others darker, and so on. That is why I believe a calculation formula is of limited use.

Of course, it is always better to see your own design in real life, but that can be quite an effort. However, if I know, for example, that 100 lux is a good guideline for a hallway in a private house, I can start with that and then adjust as needed. If I unknowingly start with 20 lux and then am disappointed, I may have to completely replace the light fixtures because I am essentially working in the wrong category.