From LightWiki

When you use a Diffuse Shader, LightWave no longer takes the Luminosity of your surface into account, so you have to add it manually.

The formula for LightWave's luminosity is:

diffuse shading + base colour * luminosity level = new shading colour

Keeping that in mind we need to recreate this equation using the maths nodes we have available.

The following image is set up for nodal luminosity. (need simpler example!!)

Image(2) contains the raw colour information, Image(3) is the luminosity level.

Image(2).Color -> Scale(1).Vector : The Base colour

Image(3).Luma -> Scale(2).Vector

Scale(2).Result -> Scale(1).Scale : ...is scaled by the Luminosity level.

Image(2).Color -> Lambert.Color : The Base colour also controls the Lambert diffuse shader

Lambert.Color -> Add.B

Scale(1).Result -> Add.A  : The result of the Lambert shader is added to the result of the scaled luminosity