Light source is weak. Polymer manufacturer stated a 2-4 minute exposure. 3 minutes only got me to 10 on the Stouffer guide. Recommended is 16. As my films are not super dense, I got a good plate with 10min. If you need high throughput, get a more expensive unit. The review complaining about the interior not being black? You don’t have a point light source, your LEDs are spread all along the bottom so reflectivity is the least of the problems. Besides, who’s to say the paint is reflecting uv anyway? If you’re looking for high-detail plates, you’re not buying a sub$200 exposure box.