Problems With Lighting
I released my first map on to the forum yesterday and though it was generally well received by the community. But there are some problems with the map that I can't seem to solve on my own. I'm terrible at lighting...
I have a couple of observation rooms that acts as the main light source. There is also a couple if light spots highlighting the small areas of destruction of the map. It's the sealing that seems to get the worst lighting.
When I compile my map I get a ton of yellow errors, all of them saying something like:
WARNING: Too many light styles on a face at (639.000000, -55.999992, 248.000000)
The problem is that I can't seem to get rid of them. I've removed every single observation room and light_spot from the map (leaving in the light sources from the instances) but the errors are still there.
What can I do to change this? Does it matter? What can I do in the future to get better lighting?
I also get this yellow error when compiling:
ConVarRef gpu_level doesn't point to an existing ConVar
What is that all about? 
Link to the map:
CrossFlinger
In short: you have too many named lights shining on a face at those coordinates. (I think the maximum is 4.) Every light that has a name is 'cast' separately from all other lights by VRAD - so they can be turned on and off). There are two rules of thumb:
* If you don't need to turn lights on and off, don't give them a name.
* If you need to turn on or off a group of lights at the same time, give them the same name.
Additionally, the VDC has this to say:
At the coordinates specified there is a surface lit by too many "effect" lights. This includes lights that have a name (which compiles both on and off status so you could switch them) or a light using effects like flickering. Remove some of them, disable flickering effects or make sure they don't have a name.
Note: A surface may only be lit by up to 4 lights with different targetnames. This means a face can be lit by unlimited different light styles as long as they share up to 4 names.
EDIT:
ConVarRef gpu_level doesn't point to an existing ConVar
Don't worry about that, I think that's normal.
Co-operative: Lightspeed Upstairs Downstairs
* If you don't need to turn lights on and off, don't give them a name.
* If you need to turn on or off a group of lights at the same time, give them the same name.
I haven't given the lights that I've added any names. Does this include indicator lights/textures and/or instances (like a dropper) with names?
Indicators and textures no, but instances yes. The cube droppers have two named lights (one orange and one blue) as far as I can recall.
Co-operative: Lightspeed Upstairs Downstairs
I disagree. That warning doesn't really mean that. First of all, don't you care about that message much, and don't you think it IS causing weird lighting affects or somethng... What that message is meaning is that in mentioned brushes/areas you have many different light colours/brightness with so many different values... but that's all, I mean that message only warns you about this: "each of those tiles receive a lot of information about lighting, which of all those values do you really want me to apply?, please tell me, you're driving me crazy about that!" So, if you are looking for a specific colour/brightness for a bunch of tiles, go and look into the area that message if pointing to, otherwise, if you look at that area and you like the light in there, just dismiss the message.
useful tools and stuff here on TWP 
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I've gotten this message a few times before in compiling. You can usually ignore it, but if you really want it gone, it usually means you have more than 1 dropper instance in an area. The default has at least 2 named lights, I think it might even have 4 though I don't remember if the light_spots and the lights are named differently or not. I've made myself a couple dropper instances without named lights, to avoid this error.
Oh yeah, I've been meaning to do that. Thanks for the reminder!
I must say that the switching lights aren't even that noticeable, unless it's in a very dark room with a wall or floor close by.
Other Portal 2 maps: Medusa Glare
Portal 1 maps: Try Anything Twice | Manic Mechanic
Thanks for your responses.
It would be cool if anyone of you could share one of those instances
These errors don't matter too much, they only serve as a warning for possible lighting issues.
The only time you should worry about this, is if you actually have big lighting errors (typically, this will look like one brush being lit normally, but the one next to it being dark, or any kind of lighting 'seam' where there's a hard falloff on a line instead of a reducing glow)
I usually get around this problem by 'filling' the areas with lighting seams with static lights. This isn't optimal but it looks pretty good. The other option is 'cutting' your brush surfaces so no 2 light_spots are touching the same face. This is much more difficult though, and you will have to adjust the cones on your spots so they don't 'cross' each other.
Long story short, if you're not getting any dramatic ugly looking lighting, I wouldn't worry too much.
It would be cool if anyone of you could share one of those instances
This shouldn't be too hard to do yourself.... open the stock instances .vmf in hammer, SAVE AS "my_instance_name_here", goto Map > Entity Report in the menu bar, scroll down until you see light ( or light_spot), select properties, remove any name from the targetname parameter, Save. Use your own instances in the same way you would use Valves.
You might even want to remove a light (or two) and recolour the remaining one with a white/greyish/neutral light.