The glow is an effect that happens in post processing – meaning it is applied to the image after the render is done. It doesn’t actually illuminate other objects or have a direction. If you want to illuminate other objects you’ll have to make a light source, such as a spot or point or area light. If you want to see the light as if its lighting up particles in the air, you’ll need to add light fog. You can only add light fog to point or spot lights. The fog will be in a cone by default, but you could use some objects to block it and make it look like its coming from a square.

• Make a spot light.
• Turn on depth map shadows.
• In the attribute editor, click the button next to “Light Fog” to map a new lightFog node.
• Make an object, such as a sphere, and put it somewhere in the cone of the light fog.
• Render – you should see a beam blocked by an object that casts a shadow into the fog.