This is one easy way if you have some beam images taken in otherwise black darkness. I used your example beam:
This works in any photo editor which has layers and blending mode ADD. GIMP is one of them. I used Photoshop, which doesn't offer any advantage in this case.
I added 3 copies of your beam as separate layers with layer blending mode=ADD. I applied hue shift to recolor the beams, erased a little at the bottom with the eraser a (=slowly with low opacity for no edge) and distorted the shapes a little to make them different & fitting better to the perspective.
This can be done also without a beam photo, but it needs some work. You must draw the beams. You can use blurring or gradients or both of them. GIMP's circular motion blur would be especially effective for the conical beam because you will get radially expanding blurrines. Draw a sector with gradient fill and give to it circular motion blur.
A complex thing is how much you want to include the non-idealities of normal cameras such as
- color and background item contrast loss (=whitening) at bright areas due overexposure
- lens flares
Here's one home made light beam and its parts without blur.
Making it yourself gives some freedom. Here the color is more saturated. I guess a colored light cannot be simpler. There are only 3 parts in separate layers:
The red glow around the lamp. It's a blurred red ellipse with blending mode Hard light. The opacity is 75%.
The spot on the floor is like the glow around the lamp, but bigger. The opacity is 50%.
The beam is a selection which has been filled with a gradient. The selection is drawn with the pen. The gradient is radial white-red-transparency, red has opacity = 40%, white is opaque, blending mode = Normal. White presents overexposure in the camera. The shape has got circular motion blur.
More plausible result needs some weak color also on the walls.
Warning: The job turns to a complex one as soon as you want to have some items or persons under the beams. Getting their lights and shadows right is far from trivial.