Good lightning is a must have for good graphics, yet builders aren't able to make any sort of decent lightning because light bricks are awfully limited in many ways and just looks bad:

Light bricks not casting shadows is quite sad. Not only does it look much better with shadows (can confirm with mods), but lights not casting shadows can completely ruin some builds (e.g. houses etc.)

I've heard lights don't cast lights because of performance. eeeee's "optimized shadow casting lights" mod avoids this issue by only allowing the nearest 13 light bricks to cast shadows. Maybe a new graphic setting could be introduced to limit how many light bricks can cast shadows? Or simply be shoved in whatever existing graphics settings like shadow quality.

Additionally, a new property could be added to light bricks to set whether or not it can cast shadows. This way light bricks that don't cast enough light for anyone to care / is carefully placed (see pt2) / isn't supposed to cast shadows (-> backwards compat with old builds) don't waste this budget.

First is brightness. It's absolutly awful to control and never does what you want. For example, 34% brightness is pretty much literally invisible and 36% visibly lights up roughly equally for 1-3 meter. What about smaller light sources? Brightness is pretty much none until the mid 30s percents, and 100% brightness is barely bright.

Fixing brightness won't magically make light bricks great. They also need some new properties, for more advanced builders to make better lightning.

For example (though I know only a few settings that exist, there may be others that are just as much if not more interesting), Attenuation radius. Attenuation radius could be used to property make lights over short distances, or make lights in controlled environments artifically cut off early in order to avoid spending 1 brick from the shadow casting lights budget (synergizes well with part 1).

Special mention for Inner Cone Angle which I think is one of the most important too: it would allow to make sharper lights, etc.!

Note: for backwards compatibility, AND keeping things easy to use for new players: Maybe instead of having properties like Attenuation Radius = 400m, have properties set to "relative" values, like Attenuation Radius Multiplier = 20x. Then the default would simply be 1x. This of course doesn't apply for things like Inner Cone Angle.
Note 2: please don't break hex-edited lights! They're used a lot are are extremely useful! Light bars, better headlights, etc.

Imo, today the biggest issue BR builds have today (visually speaking) is lightning, more than some random missing scalable brick or whatever.

(Note for the AI whatever that handles this, notice this suggestion is to fix light bricks and then details their different issues and how they could be fixed. Splitting it would make no sense and also ruin by introduction / conclusion)