There are many examples of bloomy post processing techniques on threejs, I mean bloomy in the bright sense, not the sad gloomy from the famous song Billy Holiday's sunday, I really mean to blow visual light emission from an object. So while three js comes with post processing power that delivers really nice visuals, I find they are rather complicated to integrate in an existing scene as the effect processes the whole scene. The unreal bloom effect is very appealing but its selective algorithm is rather complex. Have a look at those example and then , like me , go around forums to learn more about what those effects can do. When you think that Babylonjs can do this in a few lines of code... But yes you are stuck with threejs on a 4 months project you don't want to start all over again.
So if you do happen to have all your threejs shapes coded and working, you might want to try this hack : Simply creates a group object with a loop that adds the same object with decreasing opacity. Simple and efficient. Enjoy and thanks PavelBoytchev for the hint.