Forward Raytracing vs Bounce from Surface

I’m trying to understant the difference between this two components. At first it sounds obvious, but when I use them, Its less evident.

I’m trying to form a sort of reflector SRF that will bounce the sunlight towards the interior of an atrium. The sun Light should pass through the open area (glazing) of a skylight construction (see image)

Which of this two components should I be using. BTW it depends on the time of day and year the BounceFromSurface component returns a non bounce message. While the other (forward ray tracing) does intersects with the reflector geometry.

Any ideas


Hi Claudio,

As far as I understand, the only major difference between the two is that the bounce from surface has you input the geometry that you want to see sun vectors bounce off and automatically generates start points of the sun rays based on a gridSize or density of sun vectors. On the other hand, the forward ray tracing makes you input start points for the vectors, forcing you to generate the grid of points yourself.

Personally, I have usually found the bounce from surface to be more helpful in most cases, particularly in those like the one you are looking at here, since, if you use the gridSize, the number of sunrays getting through will usually have a pretty good correlation to the amount of light getting into the space. If you are not getting any sunrays in with the bounce from surface component at a time you expect to be getting them, you should try dropping down the gridSize.


Hi Claudio,

As Chris said Forward Raytracing is the most useful when you don’t have a target surface, otherwise they are both doing the same thing.


Thanks Mostapha And Chris Is much clear now.

One thing : Is it possible to isolate the last bounce only coming from the SourceSrf. For instance in an exterior condition where a building reflects sunlight onto a specific area. I will like to now which are the rays reflecting from the SourceSrf that reaches a given target area (a park or house) As the component not only shows reflected rays it also draws the sunrays tha directly touch any context geometry.

thank you