int g_num_lights;
float g_time;
float g_occlusion_radius;
float g_occlusion_max_distance;
float4x4 g_mat_view_inv;
float2 g_resolution;
sampler2D smp_position;
sampler2D smp_normal;
sampler2D smp_occlusion;
float4 ps_main(float2 tex : TEXCOORD0) : COLOR0
{
float4 res = 1;
float4 albedo = 1.0;
float4 position = tex2D(smp_position, tex);
float4 normal = tex2D(smp_normal, tex);
float4 occlusion = tex2D(smp_occlusion, tex);
float4 lighting = 0.0;
float3 point_light_positions[3];
float time = g_time*0.75;
float light_rad = 2;
point_light_positions[0] = float3(light_rad*sin(time), light_rad*cos(time), 1);
point_light_positions[1] = float3(light_rad*sin(time+1), light_rad*cos(-time+2), 1);
point_light_positions[2] = float3(light_rad*sin(time+2), light_rad*cos(-time+1), 1);
float3 point_light_colors[3];
point_light_colors[0] = 2 * float3(1,0.2,0.2);
point_light_colors[1] = 2 * float3(0.2,1,0.2);
point_light_colors[2] = 2 * float3(0.2,0.2,1);
for(int i=0; i<g_num_lights; i++ )
{
float3 light_pos = point_light_positions[i];
float3 to_light = position.xyz - light_pos;
float to_light_dist = length(to_light);
float3 to_light_norm = to_light / to_light_dist;
float light_occlusion = 1-saturate(dot(float4(-to_light_norm,1), occlusion));
float dist_attenuation = 1 / (1+to_light_dist*to_light_dist);
float ndl = max(0, dot(normal.xyz, -to_light_norm));
lighting.rgb += point_light_colors[i]*light_occlusion*ndl* dist_attenuation;
}
//lighting += 0.25f * pow(1-saturate(occlusion.w),2); // ambient
res.rgb = lighting.rgb * albedo.rgb;
return res;
}

You can find shader that they are using at there https://github.com/kayru/dssdo/blob/master/dssdo.rfx

Simple dot term that they refer is that.

float light_occlusion = 1-saturate(dot(float4(-to_light_norm,1), occlusion));

So it's just dot between normalized light dir and first 3 spherical harmonics term(directional part) and then just adding 4th term(constant part) to result.