[away3d] Striplight reflection effect

[peter gledhill]

Hello,

I'm trying to create a strip light effect on a a cube like such:
http://www.enigma-interactive.co.uk/external/sandbox/peterg/away3d/strip_light_effect.swf

At the moment I'm doing this using and EnviroBitmapMaterial which
takes in a pure red (0xFF0000) and uses the following png for the
environment map:
http://www.enigma-interactive.co.uk/external/sandbox/peterg/away3d/enviromap_2.png

What I really want is for the above png to have alpha transparencies
where it is black; so that the black doesn't effect the base bitmap
and the solid pure red shines though.

However when I do this the alpha parts of the environment map seems to
become white.
http://www.enigma-interactive.co.uk/external/sandbox/peterg/away3d/strip_light_effect_transparent.swf

Can anyone suggest a way of getting this effect?

Thanks in advance.

CODE:
var light:DirectionalLight3D = new DirectionalLight3D();
light.ambient = 0.8; light.diffuse = 1; light.specular = 0.8;
light.brightness = 3;
scene.addLight(light);

var enviroMat:EnviroBitmapMaterial = new EnviroBitmapMaterial
(
        new BitmapData(500, 500, false, 0xFF0000), // solid red bitmap for
testing
        Cast.bitmap(EnviroMap),
        { reflectiveness:0.7 }
);

var cube:Cube = new Cube({width:200});
cube.material = enviroMat;
scene.addChild(cube);