A custom node for Unity's ShaderGraph to capture lighting and use it into the shader. Works as of Dec 2018, but the APIs might change!

MainLightDataNode.cs

using UnityEngine;
using UnityEditor.ShaderGraph;
using System.Reflection;

// IMPORTANT:
// - tested with LWRP and Shader Graph 4.6.0-preview ONLY
// - likely to break in SG 5.x and beyond
// - for HDRP, add your own keyword to detect environment
[Title("Custom", "Main Light Data")]
public class MainLightDataNode : CodeFunctionNode {
    // shader code definition
    // handle shader graph editor environment where main light data isn't defined
    private static string shaderText = @"{
        #ifdef LIGHTWEIGHT_LIGHTING_INCLUDED
            Light mainLight = GetMainLight();
            Color = mainLight.color;
            Direction = mainLight.direction;
            Attenuation = mainLight.distanceAttenuation;
        #else
            Color = float3(1.0, 1.0, 1.0);
            Direction = float3(0.0, 1.0, 0.0);
            Attenuation = 1.0;
        #endif
    }";

    // disable own preview as no light data in shader graph editor
    public override bool hasPreview {
        get {
            return false;
        }
    }

    // declare node
    public MainLightDataNode () {
        name = "Main Light Data";
    }

    // reflection to shader function
    protected override MethodInfo GetFunctionToConvert () {
        return GetType().GetMethod(
            "GetMainLightData",
            BindingFlags.Static | BindingFlags.NonPublic
        );
    }

    // shader function and port definition
    private static string GetMainLightData (
        [Slot(0, Binding.None)] out Vector3 Color,
        [Slot(1, Binding.None)] out Vector3 Direction,
        [Slot(2, Binding.None)] out Vector1 Attenuation
    ) {
        // define vector3
        Direction = Vector3.zero;
        Color = Vector3.zero;

        // actual shader code
        return shaderText;
    }
}

if you update your LWRP to 4.9.0, this modified node should do the trick. Message me if you have problems; I'll try to respond as soon as I'm able.

Hi, I'm getting 26 errors keeping me from making a build, on SG 4.10.0 - Perhaps this needs another update?

hi! i am getting 26 errors as well... in 4.6.0 / 4.8.0 / 4.10.0 I tested them all and there is no way to make a build :(