diff --git a/tech/light_transport.wiki b/tech/light_transport.wiki
index 91212b4..8c16ce8 100644
--- a/tech/light_transport.wiki
+++ b/tech/light_transport.wiki
@@ -6,8 +6,29 @@ What is radiant flux?
 * total amount of energy passing through a surface (measured per second)
 * Radiant flux in Watts or Joules/second
 
-Why do we not use radiant flux?
+=== Why do we not use radiant flux? ===
 
 * When we emasure a high flux val, we dont know if lots of energy through a
   small surface, or a little energy through a huge surface
 * TLDR its to ambiguous
+
+New unit irradiance
+* Flux per unit area
+* IE Watt/m^2
+
+=== Why do we not use irradiance? ===
+
+We know the surface, but we still need an angle
+* Could be lost of energy in a huge angle
+* little energy in a small angle
+
+New unit Radiance
+* Flux per unit area angle
+* W / (m^2 * radians)
+
+== Basic question ==
+
+How do we calculate how much light exits a surface point in a given direction
+
+[[maxwell_equations|Maxwell equations]]!
+