Since r144MeshLambertMaterial does not use gouraud (per-vertex) shading anymore but phong (per-fragment) shading. Lighting computations are done in the fragment shader now which means you can’t access any light intensity values in the vertex shader.
However, in the same release MeshGouraudMaterial was introduced as an addon that retains the per-vertex shading. Use it as a code template but be aware that the lights_lambert_vertex shader chunk is now inlined.