Thanks. Actually, I had found that spotlight method after posting this, but there is one problem with that. It seems that the light cone is very pointy, meaning that the spotlight starts from a single point on top of the UFO.
If I want to make it like the right, should I edit the ISA or something (I forgot that name)? Last time I checked, there was not an easy or free way to edit it… so I wonder if there is another way to achieve this without that.
Could you tackle a circular area light in addition to the spotlight? It might help create enough of a wide base. Alternatively you could try an emissive texture. You could also position several spotlights in a circular pattern, the beams might blend together into a single one creating the impression of a wider base.
Last but not least, there is another solution that does away with a light completely – you could simply create a Tube/Cone exactly the way you want it, and assign a Principled Volume as its material, and then use the emission value. The benefit of this method is that you could actually use a noise texture to create imperfections in the light cone and give it a more organic look. As an added benefit, you could also animate the noise so that it looks like the beams are shooting down like a glowing exhaust flow.