[4.4 Beta 2] Lightmaps too dim when using directional toggle

[ricky-daniel13]

Tested versions

• Reproducible in v4.4.beta2.official [a013481]
• Not reproducible in v4.3.stable.steam [77dcf97]

System information

Godot v4.4.beta2 - Windows 10 (build 19045) - Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1650 (NVIDIA; 32.0.15.6603) - AMD Ryzen 3 2200G with Radeon Vega Graphics (4 threads)

Issue description

Lightmapping static lights produces way dimmer lights when lightmapping with the "directional" option enabled. Might be a regression of pull request #95888

Before rendering lightmaps

After rendering non-directional lightmaps

After rendering directional lightmaps

Rendering directional lightmaps in stable version 4.3

Steps to reproduce

• Open the scene "TestScene.tscn"
• Observe the very dim baked lighting.
• Click on the Lightmap3D node
• Under "Data", click to replace the Light Data file, and pick "TestScene.lmbake" (A lightmap baked without the directional option)
• Observe the almost correctly lit lighting.
• Disable the Lightmap3D node.
• Observe the correct lighting.
  (Instead of picking lightmaps, the user can disable the directional toggle and render the lightmap again to observe the same results)

Following this steps on the 4.3 MRP with lightmaps rendered on 4.3 lead to lightmaps without such dramatic differences between them or with the realtime lighting.

Minimal reproduction project (MRP)

4.4 beta 2 MRP:
lightmap4dot4beta2.zip
4.3 MRP:
lightmap4dot3.zip

[BlueCube3310]

See #96114 (comment)

In summary, since 4.0 static lights are baked with a slightly incorrect factor, which makes them appear softer than intended. Before 4.4 the directional lightmaps would be baked with incorrect coefficients that caused the directional data to be too intense, so this issue wasn't noticeable. Since dev-2 the coefficients have been corrected, so this issue has become apparent