The model for the light beam is simply white... Why is it simple white? Light has a source. Close to the source it is bright and away from the source it´s getting less visible.

The light in the air is only visible because it gets reflected by particles like dust. Dust flying in the air is no clean white surface. It´s more like smoke.

The lightning doesnt match. It´s unrealistic. THe wall with the light picture is dark because it has to be dark because otherwise the picture wouldnt be very well visible. It is very difficult to keep the rest of the room like the table with the projector bright. It would be good if it would that easy. But that isn´t realistic.

Light beams are mapped from inside to outside. For example for a flashlight I would simply create a cylinder flipp the normals and delete the bottom. Then I would rotate it forward to the default view direction. Then I would make a gradient texture from white to black add some noise and turbulence and then slightly color it yellow with colorbalance. Then I would smooth the noise with a blur filter a little bit. Simply unwrap the model and load the skin.

Then attach it to the flashlight and give it the bright flag.