Some might like their dungeons dark and dangerous^^, for all who want them as bright as possible, have a look at the following screenshots and tips.
To change the settings for the lightmaps go into the launcher.
<div class="cntr"><img src="http://img695.imageshack.us/img695/7762/33739593.png"/></div>
<div class="cntr"><img src="http://img97.imageshack.us/img97/7963/56594420.png"/></div>
<div class="cntr"><img src="http://img693.imageshack.us/img693/251/71902022.png"/></div>
For maximum brightness set the lightmap-quality to 'No shadows'.
<div class="cntr"><img src="http://img199.imageshack.us/img199/8892/43686168.png"/></div>
Setting the quality of the lightmaps to 'No Shadows' will not have an influence on already calculated lightmaps, so you have to <em>delete already existing lightmaps</em> in your cache.
<div class="cntr"><img src="http://img69.imageshack.us/img69/7814/10229405.png"/></div>
There is one exception i know so far:
The mod '<a href="http://trackmaniarpg.blogspot.com/2009/07/mods.html#Seas">Under the Seas</a>' (used for example for '<a href="http://tmnforever.tm-exchange.com/main.aspx?action=trackshow&id=1571978">Poseidon's Wrath</a>')