diff --git a/include/light/light.h b/include/light/light.h
index 5aa4f7b8..dfba8aa4 100644
--- a/include/light/light.h
+++ b/include/light/light.h
@@ -223,6 +223,9 @@ extern lightsample_t minlight;
 
 extern sun_t *suns;
 
+extern int dump_facenum;
+extern bool dump_face;
+    
 /* command-line options */
 
 typedef struct {
@@ -294,6 +297,8 @@ Face_MakeInwardFacingEdgePlanes(const bsp2_t *bsp, const bsp2_dface_t *face, pla
 plane_t Face_Plane(const bsp2_t *bsp, const bsp2_dface_t *f);
 void Face_Normal(const bsp2_t *bsp, const bsp2_dface_t *f, vec3_t norm);
 
+void FaceCentroid(const bsp2_dface_t *face, const bsp2_t *bsp, vec3_t out);
+    
 /* vis testing */
 const bsp2_dleaf_t *Light_PointInLeaf( const bsp2_t *bsp, const vec3_t point );
 int Light_PointContents( const bsp2_t *bsp, const vec3_t point );
diff --git a/light/light.cc b/light/light.cc
index c89e128f..112060e8 100644
--- a/light/light.cc
+++ b/light/light.cc
@@ -104,6 +104,10 @@ char mapfilename[1024];
 
 struct ltface_ctx *ltface_ctxs;
 
+int dump_facenum = -1;
+bool dump_face;
+vec3_t dump_face_point = {0,0,0};
+
 void
 GetFileSpace(byte **lightdata, byte **colordata, byte **deluxdata, int size)
 {
@@ -1185,6 +1189,47 @@ CheckNoDebugModeSet()
     }
 }
 
+// returns the face with a centroid nearest the given point.
+static const bsp2_dface_t *
+Face_NearestCentroid(const bsp2_t *bsp, const vec3_t point)
+{
+    const bsp2_dface_t *nearest_face = NULL;
+    vec_t nearest_dist = VECT_MAX;
+    
+    for (int i=0; i<bsp->numfaces; i++) {
+        const bsp2_dface_t *f = &bsp->dfaces[i];
+        
+        vec3_t fc;
+        FaceCentroid(f, bsp, fc);
+        
+        vec3_t distvec;
+        VectorSubtract(fc, point, distvec);
+        vec_t dist = VectorLength(distvec);
+        
+        if (dist < nearest_dist) {
+            nearest_dist = dist;
+            nearest_face = f;
+        }
+    }
+    
+    return nearest_face;
+}
+
+void FindDebugFace(const bsp2_t *bsp)
+{
+    if (!dump_face)
+        return;
+    
+    const bsp2_dface_t *f = Face_NearestCentroid(bsp, dump_face_point);
+    if (f == NULL)
+        Error("FindDebugFace: f == NULL\n");
+
+    const int facenum = f - bsp->dfaces;
+    
+    logprint("FindDebugFace: dumping face %d\n", facenum);
+    dump_facenum = facenum;
+}
+
 /*
  * ==================
  * main
@@ -1394,6 +1439,20 @@ main(int argc, const char **argv)
         } else if ( !strcmp( argv[ i ], "-novis" ) ) {
             novis = true;
             logprint( "Skipping use of vis data to optimize lighting\n" );
+        } else if ( !strcmp( argv[ i ], "-debugface" ) ) {
+            
+            vec3_t point;
+            if ((i + 3) < argc) {
+                point[0] = atof( argv[ ++i ] );
+                point[1] = atof( argv[ ++i ] );
+                point[2] = atof( argv[ ++i ] );
+            } else {
+                Error("-debugface requires x y z coordinates\n");
+            }
+            
+            VectorCopy(point, dump_face_point);
+            dump_face = true;
+            
         } else if (argv[i][0] == '-')
             Error("Unknown option \"%s\"", argv[i]);
         else
@@ -1514,6 +1573,8 @@ main(int argc, const char **argv)
     LoadExtendedTexinfoFlags(source, bsp);
     LoadEntities(bsp);
 
+    FindDebugFace(bsp);
+    
     modelinfo = (modelinfo_t *)malloc(bsp->nummodels * sizeof(*modelinfo));
     FindModelInfo(bsp, lmscaleoverride);
     SetupLights(bsp);
diff --git a/light/ltface.c b/light/ltface.c
index 080d516f..5f737816 100644
--- a/light/ltface.c
+++ b/light/ltface.c
@@ -156,7 +156,7 @@ TriArea(const dvertex_t *v0, const dvertex_t *v1, const dvertex_t *v2)
     return VectorLength(cross) * 0.5;
 }
 
-static void
+void
 FaceCentroid(const bsp2_dface_t *face, const bsp2_t *bsp, vec3_t out)
 {
     int i, edgenum;
@@ -619,6 +619,34 @@ CheckObstructed(const lightsurf_t *surf, const vec3_t offset, const vec_t us, co
     return false;
 }
 
+// Dump points to a .map file
+void
+CalcPoints_Debug(const lightsurf_t *surf, const bsp2_t *bsp)
+{
+    const int facenum = surf->face - bsp->dfaces;
+    FILE *f = fopen("calcpoints.map", "w");
+    
+    for (int t = 0; t < surf->height; t++) {
+        for (int s = 0; s < surf->width; s++) {
+            const int i = t*surf->width + s;
+            const vec_t *point = surf->points[i];
+            
+            fprintf(f, "{\n");
+            fprintf(f, "\"classname\" \"light\"\n");
+            fprintf(f, "\"origin\" \"%f %f %f\"\n", point[0], point[1], point[2]);
+            fprintf(f, "\"face\" \"%d\"\n", facenum);
+            fprintf(f, "\"s\" \"%d\"\n", s);
+            fprintf(f, "\"t\" \"%d\"\n", t);
+            fprintf(f, "}\n");
+        }
+    }
+    
+    fclose(f);
+    
+    logprint("wrote face %d's sample points (%dx%d) to calcpoints.map\n",
+             facenum, surf->width, surf->height);
+}
+
 /*
  * =================
  * CalcPoints
@@ -675,6 +703,11 @@ CalcPoints(const modelinfo_t *modelinfo, const vec3_t offset, lightsurf_t *surf,
             CheckObstructed(surf, offset, us, ut, point);
         }
     }
+    
+    const int facenum = (face - bsp->dfaces);
+    if (dump_facenum == facenum) {
+        CalcPoints_Debug(surf, bsp);
+    }
 }
 
 int