From ZDoom Wiki
113:Light_Fade (tag, value, tics)
- tag: Tag of affected sector
- value: New light level
- tics: How long the light takes to fade to the new level
Changes the light level in a sector gradually over a period of time until it reaches value.
//add this line to your script. it will affect a sector with tag #9. light_fade(9,225,35);