Daytime scenes should generally be low in contrast, with nice soft illumination in shadowed areas. There are three basic lights that you should include when thinking about lighting a day time scene; a light that will represent light directly shining down from the sun (Key), a more diffuse type of light that will represent ambient “sky light” (Basically a Fill), and finally there should be some indirect light that is being reflected or bounced off/around various objects in the scene.
For the key light or sun light, the best types of lights are directional or spot, generally some sort of yellow in color. Both directionals and spots have their advantages. Directional lights are great because they cast nice parallel rays of light and subsequently parallel shadows. This mimics reality because if you look outside on a sunny day, you will see that since the sun itself is so far away, the shadows that are casted appear directly parallel and do not diverge as they get further away from the object as you would normally get with a spotlight that illuminates with light rays that radiate outwards from a central point. However, if you set up a spot light with a strong intensity that is far enough away from the object with a narrow enough cone angle, you can get the same effect as a directional light, plus some extra control.
The sky or fill light can essentially be a copy of your key light, but with about half or a quarter the intensity, and a blue color to neutralize the yellow color of the sun. The stronger the fill light, the more evenly the scene will be lit for a more “cartoony” look. To start off with, you can usually place this light 90 degrees away from the position of the key to provide a nice even fill.
The last type of lights should be the “finishing touches”. Look at your scene rendered with both the key and the fill, and see what areas need some bounced light to make the scene more believable. These can generally be spot lights, but you can experiment with point lights too! You might also want to think about which objects are reflecting any lights. In real life lights bounce off of everything around them. Lights also pick up color from the objects they bounce off of. For example if you are lighting a scene with a red wall and white floor and the key light is hitting the red wall, you might add a red spot light that points from the wall to the floor to simulate how that light would bounce in real life. Here is also a good place to play with the decay setting in your controls to get realistic fall-off with distance.
Keep in mind also that the overall tint of the final render may require that you play with the color and intensity of the key and fill. If your scene is being shot at sunset or late afternoon, an orangish tint might be desirable, while a blueish tint would be more appropriate for dusk or an overcast day.
Night Lighting Guidelines:
The same general principles that apply to lighting a day time scene also apply to a night time scene. Its best to start with the same three light system, with moonlight replacing sunlight, but similar sky or fill lights and more indirect lights. However, one important thing to keep in mind is that moonlight is much dimmer than sunlight, so be sure to adjust the brightness accordingly.
Be careful when approaching the overall look of a night time render; naturally you may tend to think that a night time scene is really dark, but instead of making the image darker, try adding more contrast. Use weaker fill lights in relation to the fill lights, and if there are a lot of shadows in your scene, make sure not to leave them black! Use subtle cool colored indirect lights to give your shadows extra depth; it is best not to change the actual shadow color from pure black. Setting the shadow color to anything other than black brightens the shadow, because it is letting light partially leak through an opaque object, which can often create an unrealistic looking scene. This is due to having a shadow that is visibly lighter than the unlit side of the object (the side facing away from the light.) For example, if you have a blue tint to your shadow, but no blue light appears on the unlit side of the object, the shadow seems detached from the object.
When starting to light a scene it is usually best to start with a 3 point lighting scheme and build from there. First thing I do is decide where the main light source is and place a light for that source. Then I add a fill light so the shadows aren’t black. Then I start looking at objects to see what might need a fill light. After I have the general set up I start adding lights as I want little changes to the overall look. You don’t necessarily need very many lights to do a great job.
Contact shadows help with the feeling of a scene a lot. Use negative lights and link them only to the object you want to create a shadow on. Or you can create negative lights with white shadows to add specific contact shadows.
Another thing to think about is what color you use on objects in the foreground vs. the background. Try to think about what colors will make things look like they are in front or in back (for example warm colored objects look like they are closer and cool objects look like they are in back. If you have a blue and red object at the same distance, the red will look closer and the blue will look farther away.) Also closer objects tend to be more saturated.
You might also want to think about if any wall or objects are reflecting any lights. In real life lights bounce off of everything around them. Lights also pick up color from the objects they bounce off of. For example say I am lighting a scene with a red wall and white floor. If the main(key) light is hitting the red wall. I might add a red spot light that points from the wall to the floor to simulate how that light would bounce in real life.
Light Linking
Linking lights is EXTREMELY helpful when you start lighting a scene, because you can specifically control exactly what light illuminates what object. There are two ways to do this; either by using the light linker, or manually by selecting the light, then selecting the object you want illuminated, and clicking on the “create light links” button in the lighting/shading menu. Make sure you have “illuminate by default” clicked off in your light options. Similarly you can break light links by clicking on that option.
As you start adding more and more lights it can get confusing exactly how every light in your scene is affecting the scene. You might think one light is doing one thing but its actually doing something else. There are two good ways to figure out what your lights are really doing. You can hide all of the lights in the scene except for one and render. Then you will be able to see exactly what that one single light is doing. You could also check to see what a few lights are doing at a time by setting their colors to different saturated colors.
Gobos
As some of you have already experienced with the fruit bowl assignment, gobos (or cookies) can lend some great visual variation in your scene. They can break up a light or project a pattern, such as leaves on a forest floor to simulate light filtering through the canopy. You can choose to approach this traditionally, with an actual object in front of the light, or you can map an image into the light’s color channel which will achieve the same effect with less mess.
Barn Doors
There is a barn door option on spotlights which will allow you to crop light horizontally or vertically, limiting the coverage of that light to less than its natural cone angle (great for light coming through windows!).
Light Fog
Light fog can add really neat atmospheric effects into a scene, and can also simulate dust, steam etc etc for whatever purposes you need. This option can be found under the light effects controls in a spotlight. Clicking the checkerboard to the right of the Light Fog option will create a new shape node lightFog1, a new blue cone that will appear in your viewport. Make sure that you adjust the size and scale of this blue cone, because fog will only appear within the interior region of the cone. By scaling the spotlight itself, the cone will scale along with it because it is a child of the spotlight’s transform node. To avoid hard edges, I generally like to have the cone of the fog extend beneath the ground plane so that its all nice soft fog, since the cap of the cone cuts off very abruptly. Now you can play with the intensity and spread of the fog to achieve a look you like. You can also map images into the color and density channels found under the lightFog1 node to produce a less evenly gradated fog.
Environmental Fog
Environmental fog simulates the effect of fine particles in the air (for example, fog, smoke, dust). To set this up, go to the Materials tab of the Create Render Node window, and you will see an option for Volumetric Materials. These describe the physical appearance of phenomena which occupy a volume of space in the real world. There are a number of options you can fiddle with here to fine tune your fog! Some useful controls are Blend Range, which measures the vertical distance over which environmental fog gradually fades from full density to zero density, the Min and Max Height, which measures the minimum and maximum height from the origin within which the fog exists, and Use Layer, which you can use to assign a texture to the Layer attribute to create variation in the density and color of your fog. There is also a control for Saturation Distance, which measures the distance from the camera at which environmental fog becomes fully saturated (that is, its color value reaches the color setting). The Saturation Distance affects how much objects within or behind the fog are obscured.