Regarding lightning, how do you know if you need to light up a scene? Why is it that sometimes when you film a scene, you need to put light stands to light up a scene?
Example if you filmed a scene in the living room. You can just use the light on top of the ceiling. Why do you need to put light stands, example: three light stands to light up a scene?
The short answer is "you don't necessarily need to, but the less light you have in a space, the wider your aperture needs to be and the shallower your focus will become." This works if you just want to take a picture of a flat thing that doesn't move. You can just leave the aperture all the way open and focus on what you want to shoot. The moment things start to move, they come in and out of your focus range and the greater the distance between the closest and furthest from your lens that you want to shoot, you need to have a higher (smaller) aperture so you need more light to hit your subjects. The longer your exposure, the more still your subject needs to be if you want to keep a tight focus.
Add to this, your eyes are amazing creations. Coupled with your brain, they can change focus and adapt for white balance almost immediately as you look from one thing to another. They will adapt to remove shadows from one thing and balance all the information that comes into your eyes to create a single 3D picture for your brain to input and that all happens in real time.
Cameras aren't like that.
If your only light source comes from above, once your aperture is open enough to actually get a visible picture in your lens, shadows and light discrepancies will be very apparent in your picture. So you need to bathe your subjects in as much white-balanced light from multiple angles as possible. And do NOT under-estimate the power of a good white balance. We've all seen those horribly yellow or blue images which are the result of poorly-balanced camera settings.
Your light source must be the same light temperature as the existing light in a room. If your light is sunlight streaming into your room, that usually means you need to add blue gels to your white electric lights (or gold if you're shooting with sunset or sunrise light).
The more light you have on a subject, the deeper your focus can be AND the better your colour will appear in the resulting image. It also means that the more light you have, the faster shutter speed you can use and moving object will remain crisp in the image and not blurry or smoothed-out.
For the record, For most of my scenes I actually use 6-8 lights. I triangulate my 1K (1000 watt) lights on either side and spot those for a tighter focus of the light and then I fill in the gaps with huge light boxes that throw a very defused light to fill and soften shadows. I then will add a floor light or two to keep shadows from forming under people's arms or chins (or assholes) and occasionally I''ll shoot a .4K light at a white ceiling to bounce down and give everything a nice sheen from above. Every time you move the cameras more than a few inches, you need to move your lights or you'll start having light and dark fields on people's bodies or places in their surroundings.
Play with lighting things and see which effect you like the best. There are times I've intentionally used shadows and flares for effect and there are times I've done the opposite.
here's a good example...
I recently shot a scene in a house with mirrored walls, white marble floor and flat white ceiling. Using just a few lights and the natural light streaming in, I was able to get a really nice image of the men but I decided to switch around the point of view to have the glass doors looking outside behind them. that meant that once I had my aperture open enough to see the men, the outside was totally blown out and looked like a big white blob. My solution was to hit them with every light I had. I had four 1K lights on them, 3 soft boxes, both floor lights and two .4K spots aiming up at reflectors I attached to the ceiling. Looking at them with a naked eye was almost blinding, but it meant that I could bring my aperture closed all the way to a 16 so they were lit well enough to see them and my background wasn't blown out. That also meant that my focus depth was huge and the area behind them was crispy in focus even though it was about 30 feet back.
Hope that helps.
