Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 970/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 416.34
Broken: version: 2.80 (sub 51), branch: blender2.7, commit date: 2019-03-25 00:55, hash: `rB07f6be87a97e`
**Short description of error**
When you scale the Irradiance Volume to the size of a room (e.g. 6m x 4m x 2.4m), then the Distance is scaled too, and hence scaled non proportionally.
Furthermore I expected the Distance to represent an actual Distance, in particular because it expressed as one (e.g. 1 metre).
**Exact steps for others to reproduce the error**
1. Create a Cube which will be sized to be a room. Set Dimensions to X=6m, Y=4m, Z=2.4m. (This is just to compare against the irradiance volume.)
2. Create an Irradiance Volume. Scale to X=2, Y=1.2, Z=1. Set Irradiance Distance to 1m
3. Observe that the Irradiance volume now overlaps the Cube, and that due to the non-proportional scaling there is more irradiance influence in the X direction compared to Z.
Why does this matter? I would think that for architectural scenes you probably want to carefully control the irradiance volume influence distance so that indirect lighting does not extend through the wall into an adjoining room. Furthermore you do want to ensure the irradiance volume does correctly overlap the walls, and in some cases it might be important to position the irradiance probes close to the wall. Using the current non-proportional scaling, and the Distance that is actually a factor it is hard to achieve this.
Note if I import a file from 2.79 where the units were set to centimetres then unit scale is set to 0.01. This means that the Irradiance Volume requires massive scaling to get it to the correct size (e.g. 200, 120, 100) - hence the Distance must be set to a very small number - specifically 0.01m.
I note that if I create a file in 2.80 then when setting the Length to Centimetres it does not change the Unit Scale. So perhaps this is now handled better.
Based on the default startup or an attached .blend file (as simple as possible).