I'm not 100% sure from your description exactly what you're trying to achieve, I'm guessing the 'magic' door appears in open space in the middle of the barn, rather than in the wall. Is that correct?
Obviously how you achieve this will depend on the time and resources available to you, is there a reason why you must create this effect practically? In my case I would be tempted to create most of the lighting effects in post rather than on set, allowing for much more control over the final look of the shot.
I would shoot a clean plate of the barn and then shoot the door and talent with a green screen behind them and perhaps a carefully flagged HMI off to one side to throw some initial glare as the door opens and to give your talent a halo.
Then when you come to the composite you could use a volumetric lighting plugin, such as Trapcode Shine in After Effects for instance, along with glows and light wraps to craft the look of the light emitting from the door to your requirements.
There are probably many other ways to create this shot, but that's how I'd do it.