I’ve readed about some request on this but nothing done yet.
I’ve found some aproaches:
· Apply it on a material and use lightmass to calc the light but the quality seems not to bee so good.
· Light volumes but they seem to be stop developed so is not a good path to take.
· Focus a light on a plane, that’s ok but the light shape coming from a cone is a circle, anyway not too bad option.
· Make a grid of cylindrical lights, good one but you’ll get areas with more light than others and they emit for both sides.
· There are some post from 2014 speaking about a future implementation of basic shape based lights but no updated.
Obviously my intention is to have anykind of area light as is done in V-Ray, Mental Ray, Thea,Corona, Maxwell etc.
Any other idea?
There are only sphere and tube lights supported right now…Epic doesnt have an implementation for rectangular light sources. So well…you do get area lights, but not all of them 
I think there is not really a proper way to fake them especially if you want rectangular specular as well. Only thing you can do to emulate the effect is to use an emissive box/plane shape, place a wide angled spot in front of it that is the actual light source and put a reflection capture next to it so that everything getting close gets the captured reflection of the emissive box/plane. But overall, there is not really a proper solution to this for now.
EDIT: If you are using lightmass, you can also enable the light source angle which will help you to get softer shadow penumbra to even further emulate softer light coming from a box shaped source
It’s a shame we cannot get a proper solution for rectangle lights since they are one of the most used lights in arch viz.
You should be able to get very high quality results from emissive materials on rectangles by using Lightmass. You will need to make significant adjustments to your rendering settings and lighting build settings in order to get archviz-quality results, though. Check out some of the free examples in the marketplace – you can copy their settings and materials to use as a starting point. Make sure to also place skylights and sphere reflection captures!
If you need realtime rectangle/polygon lighting (moving light sources, etc.), there was a recent breakthrough presented at siggraph 2016 that can do realtime rectangle/polygon/area lighting with impressively high quality results. There is an experimental implementation of this in Unity, and as a native standalone Windows program (using the bgfx renderer abstraction library). Note that it’s a pretty expensive effect, and will rapidly grow with costs as you add more polygons to your light sources. However, there look to be a lot of opportunities for optimization (tiling, culling, etc.) and I would be really surprised if this tech does not come to UE4 in the near future, either implemented by Epic or a third party. If it hasn’t been done within the next few months, I’ll probably try it myself 