The lightning may be brighter, because you have the sun or ambiance set. This affects the overall level lightning. You can check if these are set (they are by default) in File/Map Properties under the tab 'Sun'.

Is your lightning different when you load the level with script, than without script?

The giant red block is probably not created because of this section of your script. It might be created elsewhere or it is already in the level.

To check if it is already in the level, look in the project tab (left in WED) and make sure there are no blocks that are 'off' (right click->mode; mostly, they look different in the project tab) If 'off' is set, you can see the block ingame, but not in WED.