Do not underestimate the importance of lighting terms.
Stops are Stops
Same as before, a stop is half or twice as much light. This a single unit of percieved brightness brighter or darker for the image (more or less).
"Up a stop" makes things brighter, "down a stop" darker.
Temperature is Color
Temperature, as explained in the color section. Photographers say things are "cool" or "warm", "cooler" or "warmer". Light is not (almost ever) referred to as cold or hot - the proper usage is relative.
Key, Fill, Back
Key, Fill, and Back doesn't refer to anything special about any lights. You don't buy a key light different from a fill light, although to hear photographers talk does make it sound like this.
These refer to principle lights that serve principle objectives.
Your key light is your main light. Often coming from 3/4 off camera. (45 degrees, where 0 is on the lens axis, from above).
The key light exists to give shape, detail, and definition to the subject.
The fill light fills in the shadow side. It can be a light to the other side darker, but is often a flatter (less shadows) light that is lighting the entire subject up. Usually positioned behind the camera, on the opposite side.
Fill lights get us our base exposure. If we are lighting a face, without the fill light the shadows accross the face (as given by the nose, etc) would be totally dark - which we don't usually want.
A 'lighting ratio' is the ratio between the total light (key+fill) and the key light. Don't worry about what lighting ratio's actually are mathematically speaking, but do know that photographers desribe their lighting looks as the difference between the main light and the key light.
In loose terms, this can make an image more or less 'dramatic'.
Without Fill: With fill added: Note: The reflection from the eyeglasses is from the key light. I need to change something about the angles between the glasses, light, and camera, which was done by having the subject have their glasses tilt down slightly (as seen in the no-fill light image). Photographers trick: I had the subject push up on the stems of the glasses, they aren't resting on the ears.
The back light is also called the kick light, the kicker, a rim light, or a highlight light.
This is a light positioned somewhere behind the subject, used to separate them from the background by creating a rim.
This is the photo with the back light.
And this is just the back light.
Together the image is much nicer. The subject has depth and detail.
Also note the difference in color temperature. I did not match my light temperatures on purpose, because I like the look and the way the gold light works with the blonde hair.
A background light is different then a back light.
In this case, pink. Also, this pink light is spilling off of the walls and giving our subject some back light too. That was on purpose, to reflect through the already-dyed hair.
It's a light that, well, lights up a background. Either to provide color, to evenly light a backdrop (a good green screen needs lighting separate from the subject, shadows mess up green screens!) or to create a bright area to halo behind the subject, framing them with a pseudo-vignette.
The 3 Light Setup
The classic 3 light setup is simple. A fill light gets a base exposure. A key light gives depth and detail (and is the "main" light), and a back light seperates the subject from the background.
This is the bread and butter of practical and usable lighting.
A gobo stands for "Go Between Object". Anything that goes between the light and the subject in order to block some light. I often need to keep my lights from spilling off onto the background or somewhere else I don't want, and a gobo is the thing.
What actually are gobo's? Literally anything opaque that you can position right. I often use people, if they are nearby, to hold up their hands or stand in certain spots.
A cookie is a gobo with holes in it. Or something slightly transparent. It lets some light through and can be used for interesting effects.
Often, the leaves of trees act as cookies, and the occasional ray of light gets through.
To get the following photo, I violently and randomly stabbed some cardboard with a knife and taped it like a flag to a light stand. I asked my subject if she could see the head (bright part) of my light with her left eye closed. She could, so I knew a ray of light would find her face. There was some trial and error to get the positioning right.
A snoot is a tunnel that makes light into a spotlight. I stick coffee cup holders, the ones that keep you from burning yourself, onto my lights sometimes.
A grid is basically a bunch of small snoots. You can make a grid out of a lot of straws taped together, but this is one of the light modifiers that I actually buy, since it's basically a single piece of indestructible plastic.
Grid's make a spot light, narrowing the beam, like a snoot, but the light from a grid gives soft edges.
Walk signs use grids so you can only see the sign if you are looking righ at it (accross the street), and thus you only see the appropriate sign.
I use grid's all the time. I love using them very subtley, making a photo look natural light, but, well, cheating with a little extra pop on my subject to make them brighter than anything else.
A soft box is a big panel that goes around a light. It does 2 things: It diffuses the light (makes the percieved size larger) and blocks light from spilling out of the back (unlike umbrellas).
Some soft boxes have a second internal diffusion sheet inside them. This helps the front of the soft box have completely equal illumination, but eats up more light (so it's not as bright).
I really like soft boxes.
Umbrelles are either reflective on the inside (they bounce light back) or white and diffuse (you shoot light through).
The reflective ones are more efficient, they eat up more light, but can take up more space in a studio, since the light stand is 'in front' of the light source. They can also, in reflections (like catchlights in the eye) show the arm