That's fine Duga. Nothing wrong with that effect at all.
Your's is more a sunlight rays kind of effect. To swap it out for an indoor effect, remove the spectrum colours and use only one. Preferably a dull or monochromatic tone.
My suggestion for the effect would be very simple -- as is the effect in general.
Create a selection to be the overall light screen coming through the window. This will encompass the size/shape of the window. Fill it with white and drop the Opacity a lot.
Use the Polygon Lasso tool and create the separate beams of light. Fill them with white also and also drop their Opacity.
Blur to taste.
TIP: you can use multiple layers for the beams if you like. To create an overlaying or complex effect.
