[KHR_lights_punctual] Exported intensity seems wrong (might be a GLTF-Viewer bug)

[Gpinchon]

Describe the bug
Setting up a 200W spot light results in seemingly overly powerful lights.
Only solution to get normal spot lights is to set them to 1W which doesn't make sense and makes them completely invisible in Blender. I tested the resulting export inside GLTF-Viewer and the result was the same as with my toy engine (blown out colors).
Either the intensity values are wrong, GLTF-Viewer exposition/light attenuation is wrong, or I'm missing something.

To Reproduce
Create a scene with a spotlight at 200W, export to GLTF, observe overly powerful light intensity in GLTF-Viewer. Reducing exposure to -10 is necessary (from what I've seen Blender's exposure is 0 by default)

Expected behavior
From my limited understanding : spot lights with intensities lower than 10870 candelas, the resulting GLTF should at least render correctly on GLTF-Viewer.

Screenshots
Blender result :

glTF-Viewer result :

.blend file/ .gltf (mandatory)
LightTestScene-Spots.zip
GLTF.zip

Version

• OS: Windows 11
• Blender Version 4.3.2

Additional context
It might be linked to #564
Exporting using "unitless" seems to fix the issue, but it does not seem to really make sense since GLTF-Viewer seems to have correct Exposure and tonemapping doesn't it?

[julienduroure]

Cc @will-ca