direct( { lightDirection, lightColor, reflectedLight }, builder ) {

		const irradiance = getGradientIrradiance( { normal: normalGeometry, lightDirection, builder } ).mul( lightColor );

		reflectedLight.directDiffuse.addAssign( irradiance.mul( BRDF_Lambert( { diffuseColor: diffuseColor.rgb } ) ) );

	}
Implements the direct lighting. Instead of using a conventional smooth irradiance, the irradiance is
reduced to a small number of discrete shades to create a comic-like, flat look.

@param {Object} lightData - The light data.
@param {NodeBuilder} builder - The current node builder.