After upgrading to Unity 5.5 our lighting got pretty messed up.
The scene appears almost unlit, and dynamic shadows are rendering through the floor and other static objects.
We have a single directional light in the scene, which is set to mixed.
I have tried rebaking lightmaps, but the scene remains the same.
Any ideas? 
Here’s some screenshots that show the difference:
I’ve submitted a bug report, reproducing the shadows problem. Notice that the cubes shadow is rendered on both floors. This only happens in Unity 5.5.
wow
try to change the directional light away from mixed, as its a buggy mess
I had 3 directional lights turned to max intensity, and ambient light was at max as well, and I clicked “Build”, and my scene seems unlit. Looks at this:
That is with MAX intensity. Worked fine in 5.4, not 5.5. My team member is also having trouble. What the hell happened?
I’m having problems too with lighting since I upgraded to 5.5 this morning, as light intensity values have little or nothing to do with what you get once lightmap is baked. As a result, the full process of lighting is unpredictible …
In my case I’m working on fully directional-specular lightmapped maps on IOS environment. WIth previous 5.4* versions lighting worked sweet and accurate, however now everything looks a disaster: everything looks dimmer and flat, metallic&smoothness maps are barely visible… a total mess
After doing some tests I really don’t know what to do to get back to the same visual quality than before…
what’s happen ? !!!
Unity happened…
Same for me, after upgrading from 5.3.x.
After upgrading to 5.5 and rebuilding lightmap, scene seems almost unlit (though not entirely). I had one baked light and one realtime light, both using mostly different layers in their culling mask (no lights set as mixed).
Realtime light at least seem to work more or less, so I assume this has to do with baked lightmaps and illumination.
I also have issues with lighting since upgrading from 5.3.x to 5.5: I use a terrain with one directional light and ambient lighting to simulate a day and night cycle. Since the upgrade I have the problem that the directional light seems to be weaker and is barely throwing shadows when ambient lighting is enabled as well. The result is that the whole scene lacks depth since the shadows are barely visible anymore, similar to the last two screenshots mathiassoeholm posted above. When using only directional lighting the whole scene seems to dark in total. I can of course increase the intensity of the directional light but this results in ugly, unrealistic high-contrast lighting.
I tried to achieve the same lighting quality as before by tweaking values but no good result so far, will let you know if I find anything else.
read somewhere you can put lightmap texture import setting to default texture type
but after try result is burrned on mobile !
I noticed that my issue with terrain lighting seems to be connected with normal mapped terrain textures. Here is a screenshot of the issue like I experience it:
Same scene with normal maps removed from the terrain textures:
Scene is much brighter now, shadows are clearly visible on the terrain. I did have normal maps enabled in 5.3. and it certainly did not show this issue.
I have been playing around with the normal maps since I noticed this, but I still can’t 100% put my finger on what is wrong exactly. It seems that something is off with the way normal mapped terrain textures seem to recieve light, when the light is directly on top coming in at a 90 degree angle they seem to be displayed darker than when the light is coming in in a smaller angle.
Not sure if we all experience the same issue here, but maybe it is worth if you do a quick check and remove some normal maps from your scenes if you have any to see if it makes a difference for you.
another update: the terrain normal map textures where not set to TextureType = Normal Map in the import settings, doing so resolved my problem now. Not sure why this did not affect me in 5.3 or if this was something that happened during the automatic migration processes when opening the project the first time with 5.5.
