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So there seems to be a max number of lights and when you exceed that number, the game crashes very badly.

Then don't use that many lights.
Sorry, I'm a trekkie.

Classic (though they stole the idea from 1984).

As for the OP. It was a community service announcement. I am working on reducing the number of lights and still be able to see.

Which game and editor version are you using? Is it v436 with UEd 2.0?

If so, that's normal, I had the same issue with my one of my latest maps, and it was fixed in the v469 patch, with an updated editor (UEd 2.2).

If you are maxing out on lights in a map, you certainly are using way too many lights!
The more lights in a map, the larger the map file size is.
Using a large quantity of light actors in a map can contribute a lot to the map's file size.
Adjust your lights to illuminate larger areas, rather than using more light actors, where you can do this of course.
Also, make use of zone lighting where applicable, instead of using a bunch of lights all over.

Thanks for the info. I had a large outdoor area and had max range on the lights, but too much overlap. I was able to reduce the number quite a bit.

For general information, the maximum lights that did not crash was 737.

737..................and that's a magic number.

Are you done ? Good...
Now let me detonate the fake news number from above description. We have a recent posting which demonstrates a few good looking things. Take a look here: You don't need to believe me, check the post and demo map posted... This LightPath is a subclass of Light - A Light class after all.
fake "Dynamics" shadows again..
We can talk about what is supported in Editor as Dynamic Lightning vs Textured View - these are not the same things... and I think I could figure whatever map by Alexanderr if I'm not mistaking and one by Ferali which definitely are having more lights than whatever 700+.

And then... the true story is how much memory can be accessed on 32 bits. When memory is full filled then you can expect the unexpected... or when certain constant goes over boundary, Engine will die, else render will die due to lightning data, and so on. It's crashing in less than an eye blink.

And moving to Dynamic Lightning: If you are having issues with drivers that's a different story, my rig can open maps with more than 4000 lights and then 700 it's not a limitation but a bunch of lights in the same place are not supported - LightPath sample map demonstrates that.

I wondered about that, but I checked by removing lights from totally different areas in the map. It really seemed that that 737 was the number. This even involved lights that were in different zones.

The game or editor crashes when you have too many lights densely packed into the map, but this is only true when using the editor that comes with 436.
In other words, it's not the number of lights overall, but rather how many within a small area.

Sektor gave the example of my map where I use over 4700 lights and the map works and does not crash, proving beyond any doubt that the number of lights is not a factor.

If you use the new editor that comes with 469 (Unreal Editor 2.2), you won't have any problems, since these were issues related with how the editor builds the lighting, which have all been fixed.

In case you get similar problems using the new editor, please report them.