lightmap.dat is a file used in The Sims 1 and The Sims Online to fill rooms with lighting.
When the player creates a room and has not yet put in any lights, the room score will be practically 0, although the game will still light the room up. Once the first light is added, the game makes the room bright near that light source and very dark everywhere else.
When lightmap.dat is deleted, this effect is taken away, as if no lights have been added to the room (although their sprites will switch to the on state).
lightmap.dat consists of ten 8-bit grayscale images in top-down order. These are:
|0||320x232||Unknown (light intensity ramp?)|
|74240||320x232||Unknown (darker version of above)|
|148480||256x232||Unknown (darker version of above)|
|207872||192x232||Unknown (darker version of above)|
|252416||16x2220||Wall Lighting (far)|
|287936||32x4440||Wall Lighting (med)|
|430016||64x8880||Wall Lighting (near)|
|1744256||224x112||Floor Lighting (far)|
|1769344||448x224||Floor Lighting (med)|
|1869696||896x448||Floor Lighting (near)|
You can see these images here: http://niotso.org/lightmap/