Actually, in the V-Ray Help has a very specific examples .
You come at the right section, and you look in the upper right corner. If there is a point Examples, then click on it. So you'll go to specific examples of the use of an effect😉
I'm a little caught up here, that's what I'm gettingHow I did it: created a scene, put a candle, set up lighting. We created an atmospheric gizmo sphere, applied the burning effect to it (adjusted the size, density, and type of flame). Render - the candle caught fire, but there is no shadow from it at all. Therefore, we create a light beam, place it directly in the gizmo, a spherical type, adjust the multiplier of its glow under the scene, indicate that it is invisible. Shadows appeared. Next we must apply the Bloom effect to the flame. Do a render without closing this window go to Rendering> Effects (or just 8 and go to the effects table), click Add ... and select VRay Lens Effects from the list. Turn on the bloom and click to update the effect. My computer again renders, but when I finish, I see that this render is done in an additional preview window of the effects lenses. Now you can adjust the density, size and shape of the glow, which will immediately be reflected in this new window. In principle, the effect works. BUT, as far as I understand this effect can not be tied to a particular place or object in the picture, let's just assign a glow to only the flame, as is done with standard lens effects in 3D Max. Verei himself chooses the brightest spots in the picture and applies a glow to everything at once. As we see in my example, the result is not very soft, for example. Except for the flame, there are still many bright spots (for example, as the top of the candle). I tried to increase the brightness of the middle of the flame a little, so that this piece was the brightest in the scene, and the effect was propagated from there. I created the sphere, scaled it, assigned a self-luminous mate, placed it in the gizmo - what happened you saw. The same story (even worse) occurs if we make our visual light visible. In this case, the glow of the light is many times stronger than the burning and clearly cuts the flame sharply, and still it can not be given the desired elongated shape. RenderStuff, help!Here, when the darker the effect is better seen