Mostapha I finally did some comparison, and I think that the VSC calculated with radiance does not do the job as its best, you can check results in the .zip attached.
It would be great to have a tool similar to shadow mask or sunlight hours.
I am planning to use it to calculate Sky component and create a safe envelope for Right of light, which is one of the crucial planning issue here in the UK.
Here you can find some examples of what I am talking about.
http://www.waterslade.com/services/dev_potential.htm
http://www.right-of-light.co.uk/maximum-envelopes.php
I am happy to help in any way
bye!
VSC Radiance.zip (509 KB)