diff --git a/README.md b/README.md
index 18570c2..58ef467 100644
--- a/README.md
+++ b/README.md
@@ -11,9 +11,31 @@ npm install
 ```
 Run `node ./bin/obj2gltf.js` and pass it the path to an OBJ file.
 
+## Usage
+
+###Command line flags:
+
+|Flag|Description|Required|
+|----|-----------|--------|
+|`-i`|Path to the input OBJ file.| :white_check_mark: Yes|
+|`-o`|Directory or filename for the exported glTF file.|No|
+|`-c`|Combine glTF resources, including images, into the exported glTF file.|No, default `false`|
+|`-t`|Shading technique. Possible values are `lambert`, `phong`, `blinn`, and `constant`. The shading technique is typically determined by the MTL file, but this is good for more explicit control.|No|
+|`-h`|Display help|No|
+
+###Examples:
+
+`node ./bin/obj2gltf.js model.obj`
+
+`node ./bin/obj2gltf.js model.obj model.gltf`
+
+`node ./bin/obj2gltf.js -i model.obj -o model.gltf`
+
+`node ./bin/obj2gltf.js -i model.obj -o model.gltf -c -t phong`
+
 ## Limitations
 
-This tool is still in development. We plan on adding additional features like gzip compression, binary glTF export, normal generation, and a testing suite.
+This tool is still in development. We plan on adding additional features like gzip compression, binary glTF export, and a testing suite.
 
 Pull requests are appreciated.  Please use the same [Contributor License Agreement (CLA)](https://github.com/AnalyticalGraphicsInc/cesium/blob/master/CONTRIBUTING.md) used for [Cesium](http://cesiumjs.org/).
 
diff --git a/bin/obj2gltf.js b/bin/obj2gltf.js
index 0e589dc..e405daa 100644
--- a/bin/obj2gltf.js
+++ b/bin/obj2gltf.js
@@ -18,8 +18,8 @@ if (process.argv.length < 3 || defined(argv.h) || defined(argv.help)) {
     console.log('  -i, --input             Path to obj file');
     console.log('  -o, --output            Directory or filename for the exported glTF file');
     console.log('  -b, --binary            Output binary glTF');
-    console.log('  -c  --combine           Combine glTF resources into a single file');
-    console.log('  -t  --technique         Shading technique. Possible values are lambert, phong, blinn, constant');
+    console.log('  -c, --combine           Combine glTF resources into a single file');
+    console.log('  -t, --technique         Shading technique. Possible values are lambert, phong, blinn, constant');
     console.log('  -h, --help              Display this help');
     process.exit(0);
 }
diff --git a/lib/modelMaterialsCommon.js b/lib/modelMaterialsCommon.js
index bdf084f..4ed1942 100644
--- a/lib/modelMaterialsCommon.js
+++ b/lib/modelMaterialsCommon.js
@@ -430,7 +430,7 @@ function generateTechnique(gltf, khrMaterialsCommon, attributes, lightParameters
         fragmentLightingBlock += '  ambientLight += vec3(0.1, 0.1, 0.1);\n';
     }
 
-    if (!hasNonAmbientLights) {
+    if (!hasNonAmbientLights && (lightingModel !== 'CONSTANT')) {
         fragmentLightingBlock += '  vec3 l = normalize(czm_sunDirectionEC);\n';
         fragmentLightingBlock += '  diffuseLight += vec3(1.0, 1.0, 1.0) * max(dot(normal,l), 0.);\n';