Just as a point of interest to anyone wanting to use the larger (colored) lights from Walmart:
1) The acrylic is extruded and frosted. It does not raster well, but I found it vectors lines alright at 50sp/70power on my 35w. If you have a design that's not too detailed, rastering is okay but blurry.
2) I tried to remove the screws so I could either lase the piece more easily OR replace it with nice cast acrylic, BUT. They are tiny little cheapo screws that stripped almost immediately. I got one out, but the other two were not moving.
3) I flipped the light over and burned it from the back, bottom up so the prongs did not interfere at all with the head movement, leaving about 1/4" at the bottom (of a 3" square) blank to be sure.
All in all, still worth the $5 price, but I think I prefer the $3 one which has easy access to the acrylic. I just have to give up the light-sensing feature.
Attached is a photo of the way I set the job up. Since the piece is now off the table, I put some magnets underneath to support the acrylic, making sure it's level. I used some large magnets to hold the base in place and make it easier to replace it exactly. I cut this same light about 4 times doing tests.
cheers, dee