My GLSL compiler is stricter than yours.

- Apple GLSL strongly objects to mismatched function declaration /
return value type, and similarly to mismatched function declaration /
lvalue type.

Shaders/surface-light-lightfield.frag

@@ -41,7 +41,7 @@ else
 }
 
 
-float light_sprite (in vec2 coord, in float transmission)
+vec4 light_sprite (in vec2 coord, in float transmission)
 {
 
 coord.s = coord.s - 0.5;