Lighting setup for a Spotlight.
This small tutorial will teach You how to create a floodlight. It won't deal so much with modeling or texturing as it will with how to configure a default spotlight to get a true floodlight effect.
A big mistake is to model a floodlight and put a (volumetric) spotlight right in front of it. The effect You would get that way will look somewhat like the effect in Image 1. The volumetric light effect comes together into a single point in front of the actual floodlight; the beam doesn't seem to actually come from the floodlight. If the camera is right in front of the floodlight, this problem isn't too much of an issue - but the more the camera approaches a sideways view of the effect, the more obvious it is that the light source is in front of the floodlight model. Even a glow effect around the floodlight usually won't help in those cases.
So the spotlight that creates the beam of light should be placed behind the actual model. The model should then be excluded from casting any shadows (modify panel, rollout 'General Parameters' - 'Exclude...'). Should Your project be a car, then You should exclude the bumper, radiator grille, rubber stripes, etc. (anything that's in the path of the spotlight beam) from casting shadows as well. Place the spotlight in such a way that the hotspot and falloff ("Spotlight Parameters" rollout) of the spotlight fit the floodlight model (Image 2).
(Spotlight, Floodlight)
If Your floodlight is rectangular ins shape, You could change the spotlight shape to rectangular as well in the "Spotlight Parameters" rollout. Problem is, however, that the light cone will actually be rectangular; which is an unwanted effect, especially if the light is falling onto a wall. You would get a rectangular shaped lighting effect (in most cases this doesn't look too great). The best thing to do is to change a round light cone in such a way, that it becomes oval shaped. To do this, simply use the non-uniform scaling tool, and scale the light in the desired axis. This will give the light cone an oval shape (Image 3).
"Is this what the lighting shape of a floodlight looks like..?"
"The oval alternative looks more like it."
Last, but certainly not least, You should make use of the "Near Attenuation" parameter. This will limit the light cone to start at the actual floodlight model (and not behind it, as we placed our spotlight behind the floodlight model). Image 4 clearly shows the difference. Using the "Near Attenuation" parameter in the "Attenuation Parameters" rollout fixes our problem.
"The light cone is visible behind the floodlight!"
"Floodlight" - "Floodlight"
"That's more like it..."
Use the same values for both the "Start" and "End" parameters, and set them in such a way that they are at the position of Your floodlight model's front (Image 5). "Near Attenuation" means that the light (and thus the cone of the volumetric light effect) will start to be effective at the set distance. Any objects nearer to the light source than this value will not be lighted.
(Spotlight, Floodlight, Near Attenuation)
Now add a glow effect to the floodlight model's front, so that the volumetric light effect blends in with the glow coming off the floodlight. Done (Image 6, imagine a second light and a car Yourself...).