change default lighting attributes to prevent mesh3d rendering bug

Mesh3D seems to have a shading bug, not sure how to describe it more precisely, but the images should help. This is the minimal example produced with the code below:

import plotly.graph_objects as go
import numpy as np

vertices = np.array([[-1.0, -1.0, 0.0], [-1.0, 1.0, 0.0], [1.0, -1.0, 0.0], [1.0, 1.0, 0.0], [-1.0, 0.0, 1.0], [0.0, 0.0, 0.0], [0.0, -1.0, -1.0], [1.0, 0.0, 1.0], [0.0, 1.0, -1.0], [-1.0, -0.5, 0.75], [-0.5, -0.5, 0.0], [-0.5, -1.0, -0.75], [-0.5, 0.5, 0.0], [-0.5, 0.0, 0.25], [-1.0, 0.5, 0.75], [0.5, -1.0, -0.75], [0.0, -0.5, -0.25], [0.5, -0.5, 0.0], [0.0, 0.5, -0.25], [-0.5, 1.0, -0.75], [1.0, -0.5, 0.75], [0.5, 0.0, 0.25], [0.5, 1.0, -0.75], [0.5, 0.5, 0.0], [1.0, 0.5, 0.75]])
faces = np.array([[0, 9, 11], [4, 10, 9], [6, 11, 10], [9, 10, 11], [1, 12, 14], [5, 13, 12], [4, 14, 13], [12, 13, 14], [2, 15, 17], [6, 16, 15], [5, 17, 16], [15, 16, 17], [4, 13, 10], [5, 16, 13], [6, 10, 16], [13, 16, 10], [1, 12, 19], [5, 18, 12], [8, 19, 18], [12, 18, 19], [2, 20, 17], [7, 21, 20], [5, 17, 21], [20, 21, 17], [3, 22, 24], [8, 23, 22], [7, 24, 23], [22, 23, 24], [5, 21, 18], [7, 23, 21], [8, 18, 23], [21, 23, 18]])

x, y, z = vertices.T
i, j, k = faces.T

fig = go.Figure(data=[go.Mesh3d(x=x, y=y, z=z,
                                i=i, j=j, k=k,
                                flatshading=False)])
fig.show()

This is not related to the saddle point per se and it is also not just an interpolation issue, as similar problems occur with flatshading=True on a parabola:

Interestingly, when I tried to get a minimal example with flatshading by isolating the problematic triangles around the centre of the parabola, the problem disappeared. So it seems to be related to some kind of scaling issue (like min/max slope or similar). Not sure whether this is actually plotly.py or rather plotly.js.

Any ideas?

Comienza ejecutando el ejemplo mínimo de Python Mesh3d incluido en el issue y compara su renderizado con flatshading habilitado en el ejemplo de la parábola. Rastrea los valores predeterminados de iluminación de Mesh3d y determina qué cambios en los atributos evitan los artefactos de sombreado; se considera terminado cuando ambos ejemplos reportados se renderizan sin el bug descrito.