surface
bulb(
	float Ks = 1.0,
		Ka = 0.8,
		Kd = 0.8,
		Ksilh = 0.05,
		roughness = 0.1,
		silhrough = 0.55;
	color specularcolor = 1)
{
	normal n = faceforward(normalize(N), I);
	vector i = -normalize(I);

	float d = n.i;
	color y = color(1.8,1.8,1.0);
	color l = ambient() + diffuse(n);
	
	Oi = 0.8*d;
	Ci = Oi*mix(l, y, d);
}