# Objective
A question was raised on Discord about the units of the `PointLight` `intensity` member.
After digging around in the bevy_pbr2 source code and [Google Filament documentation](https://google.github.io/filament/Filament.html#mjx-eqn-pointLightLuminousPower) I discovered that the intention by Filament was that the 'intensity' value for point lights would be in lumens. This makes a lot of sense as these are quite relatable units given basically all light bulbs I've seen sold over the past years are rated in lumens as people move away from thinking about how bright a bulb is relative to a non-halogen incandescent bulb.
However, it seems that the derivation of the conversion between luminous power (lumens, denoted `Φ` in the Filament formulae) and luminous intensity (lumens per steradian, `I` in the Filament formulae) was missed and I can see why as it is tucked right under equation 58 at the link above. As such, while the formula states that for a point light, `I = Φ / 4 π` we have been using `intensity` as if it were luminous intensity `I`.
Before this PR, the intensity field is luminous intensity in lumens per steradian. After this PR, the intensity field is luminous power in lumens, [as suggested by Filament](https://google.github.io/filament/Filament.html#table_lighttypesunits) (unfortunately the link jumps to the table's caption so scroll up to see the actual table).
I appreciate that it may be confusing to call this an intensity, but I think this is intended as more of a non-scientific, human-relatable general term with a bit of hand waving so that most light types can just have an intensity field and for most of them it works in the same way or at least with some relatable value. I'm inclined to think this is reasonable rather than throwing terms like luminous power, luminous intensity, blah at users.
## Solution
- Documented the `PointLight` `intensity` member as 'luminous power' in units of lumens.
- Added a table of examples relating from various types of household lighting to lumen values.
- Added in the mapping from luminous power to luminous intensity when premultiplying the intensity into the colour before it is made into a graphics uniform.
- Updated the documentation in `pbr.wgsl` to clarify the earlier confusion about the missing `/ 4 π`.
- Bumped the intensity of the point lights in `3d_scene_pipelined` to 1600 lumens.
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
* 3d_scene_pipelined: Use a shallower directional light angle to provoke acne
* cornell_box_pipelined: Remove bias tweaks
* bevy_pbr2: Simplify shadow biases by moving them to linear depth
* bevy_pbr2: Add support for most of the StandardMaterial textures
Normal maps are not included here as they require tangents in a vertex attribute.
* bevy_pbr2: Ensure RenderCommandQueue is ready for PbrShaders init
* texture_pipelined: Add a light to the scene so we can see stuff
* WIP bevy_pbr2: back to front sorting hack
* bevy_pbr2: Uniform control flow for texture sampling in pbr.frag
From 'fintelia' on the Bevy Render Rework Round 2 discussion:
"My understanding is that GPUs these days never use the "execute both branches
and select the result" strategy. Rather, what they do is evaluate the branch
condition on all threads of a warp, and jump over it if all of them evaluate to
false. If even a single thread needs to execute the if statement body, however,
then the remaining threads are paused until that is completed."
* bevy_pbr2: Simplify texture and sampler names
The StandardMaterial_ prefix is no longer needed
* bevy_pbr2: Match default 'AmbientColor' of current bevy_pbr for now
* bevy_pbr2: Convert from non-linear to linear sRGB for the color uniform
* bevy_pbr2: Add pbr_pipelined example
* Fix view vector in pbr frag to work in ortho
* bevy_pbr2: Use a 90 degree y fov and light range projection for lights
* bevy_pbr2: Add AmbientLight resource
* bevy_pbr2: Convert PointLight color to linear sRGB for use in fragment shader
* bevy_pbr2: pbr.frag: Rename PointLight.projection to view_projection
The uniform contains the view_projection matrix so this was incorrect.
* bevy_pbr2: PointLight is an OmniLight as it has a radius
* bevy_pbr2: Factoring out duplicated code
* bevy_pbr2: Implement RenderAsset for StandardMaterial
* Remove unnecessary texture and sampler clones
* fix comment formatting
* remove redundant Buffer:from
* Don't extract meshes when their material textures aren't ready
* make missing textures in the queue step an error
Co-authored-by: Aevyrie <aevyrie@gmail.com>
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
