While we're on the topic of light, I figured I'd give my suggestion out now.
Basically, a tile's lighting consists not of a number, but many, many numbers. These numbers don't represent the "lighting" of the square, but rather the rays of light passing through. A single tile would have up to 27 possible entries in the lighting, one for each direction and one for light originating from the tile. Each direction would then have a mixture of light from different wavelengths; to simplify this, microwave, far infared, infared, red, green, blue, UV, and X-ray can be used as an approximation of the common range (there are 8, so the numbering can be simple). Each wavelength would then have an intensity, which can be packed into a 2 or 3 bit value. For example, at midday the sun's lighting on an aboveground tile may be as follows:
null,null,null,null,
[1,4,6,7,7,7,3,0],
null,null,null,null,
null,null,null,null,
null,
null,null,null,null,
null,null,null,null,
null,
null,null,null,null,
As the moon shines in the west and a nearby campfire radiates from below:
null,null,null,
[0,0,0,2,2,2,0,0],null,null,
null,null,null,
null,null,null,
null,null,null,
null,null,null,
null,null,null,
null,null,null,
[0,1,2,2,0,0,0,0],null,null
And when a firefly lights up some beautiful blue light while the stars shine with the lack of clouds:
[0,0,0,1,1,1,0,0],[0,0,0,1,1,1,0,0],[0,0,0,1,1,1,0,0],
[0,0,0,1,1,1,0,0],[0,0,0,1,1,1,0,0],[0,0,0,1,1,1,0,0],
[0,0,0,1,1,1,0,0],[0,0,0,1,1,1,0,0],[0,0,0,1,1,1,0,0],
null,null,null,
null,[0,0,0,0,0,3,0,0],null,
null,null,[0,0,0,0,0,1,0,0],null
null,null,null,
null,null,null,
null,null,null
While it may be straining on FPS, this system allows for gigantic mirrors focused on enemies, fireflies with varying colours, etc. Imagine lighting a campfire and setting up black screens with the sole purpose of producing shadow puppets on a wall. Or, imagine fort mode after a terrible lack of clouds has persisted for a few days, and the grass is on the verge of igniting, while your firefighting dwarf squad is in the hospital because of UV-related sunburns. The system even allows for severe solar ejections that produce huge amounts of microwaves that are absorbed into most things, but cause dielectric heating in the poor woodcutter, heating his bodily fluids to the point of exaustion.
And, deep inside, I've always wanted to take X-rays of the dwarves.