An easy way is to use a plane grid in front of the area-light source with transparency, opaque around the edges and gradually transparent towards the center,that will make your source smaller so make it bigger(biger area-light source).
This grid opaque edges will obviously hide the environment behind it so here is a better and faster way:
-Use just a glossy/blurry refraction shader on this grid in front of the light source,it will just make the light source smoother blured ( have this grid to NOT cast shadows). EDIT: NOTE--After some tests (XSI+MentalRay3.4) I found that this grid's glossy/blury refraction shader exibits a wierd result, I couldnt get the Blured refraction show on my objects reflections (!) although when you look at the light source , through this grid, the area light source looks blured(!). I ONLY got the [b]correct[/b] blured refraction result show up 'blured' on the objects reflection, when I use the L-Glass shader (a must..exists for both xsi and maya) on the grid. It didnt work with other simple glossy/blury refractive shaders like Phong etc..(!) (Of course in all tests I have high ray depth value in the Render Globals Tab so its not that that is causing the problem) With L-Glass you get a parameter under the 'Glossy' tab called (ray) 'depth' .That needs to be set to: value = 2 to get the right results . Only then we get correct results!!! [[img]http://img184.imageshack.us/img184/8364/testsbi0.jpg[/img]](http://imageshack.us) (Both red balls are reflective with sharp-crisp specular-reflections)
-This is generally a very serious problem , it means that if we use for exmple an area light as a sunlight and we have say…blurry/glossy refractive windows in an indoor scene , we cant render the blured refraction on reflective objects…the reflection wil look as if we havent used glossy/blurry refractions for the windows.(…With L-Glass it works correctly though)
If someone can pop in and explain to us why this happens..I personally think that its due to all basic shaders (at least the ones in XSI) have a limitation for the glossy refractions 'ray depth'.
(I will also post this in the Lighting & rendering forums and I 've posted it in XSIBASE too,in case it is an XSI specific ‘problem’.)