---Since my pipe had two screw on caps with holes in to connect other pipes to it, i had to block both the holes. The front one was to be the light 'window'. The other one i used the plastic transparent glasspiece that i took out of the lantern, as it fitted perfectly.
---Put a thick lining of sillicone around the inside edge of the screw on cap, and push the plastic piece into place, avoiding too much stray sillicone(keep it clean and neat :P). I figured i could use this extra pipe attatchment hole to add a mechanical arm or some other device to it. Smear some more sillicone around the screwing rings of the cap. Then screw the cap on tightly and let dry.
---Now for the lamp window.
Sand the chrome light reflection plate so that it is slightly smaller than the rim of the cap.
Now trace the shape of it plus 3mm extra onto the plexiglass and cut it out. Make sure it fits tightly into the cap.
Then put a blob of hot glue in the center of the chrome reflector plate and stick it in the center of the plexiglass circle.
Now let it dry.