P. 62 BMM in the fourth paragraph of Light section, there are rules for illuminating other levels, than ground level of a hex. The only situations I can think of where it may be useful in BMM are when you are dealing with:
1. a 'Mech on top of a building or inside of a building on a level different, than a ground level,
2. a 'Mech using UMU to move in water above the bottom level.
The problem with those rules is, that they say, that a player may specify any level from 1 to 29 to illuminate. This means that a unit that is two or more elevations above ground level, but below level 1 (like a 'Mech using UMU with legs on depth 2 in depth 4 water or a 'Mech in a building hex which has a ground floor at sublevel 4, while the 'Mech is in sublevel 2) could not be illuminated.
I can think of two possible ways to solve this problem.
A simplified solution would be to allow a 'Mech to illuminate any level, or "any level 1 to 29 levels above the level of the chosen hex", or "any level up to level 29" (which seems to agree with the errated rules for searchlights on p. 57 TO).
A more realistic solution would be to allow to illuminate any elevation up to searchlight's range -1 above or bellow the elevation the unit with a searchlight is at. Such change should be easily done on p. 57 TO, but may not be suitable for BMM, as it would likely require to properly differentiate between ground level and an elevation relative to a searchlight equipped unit, and BMM just does not define or use the term "elevation".
