Red Light
From Halopedia, the Halo wiki
The Red light is a Forge item in Halo 3.[1]
The red light can only be added to the level Sandbox. Only two at a time can be added. The red light casts a red glow over a significant area, and is used to show that the base belongs to red team. The red light's counterpart is the blue light.
If two red lights and two blue lights are added to the same map variant, they do not cast light, they simply glow. There is one red light and one blue light on Sandbox by default.