Is this Dogs Bottom

"Here’s a simplified light path of a fluorescence microscope. We start with a high-intensity mercury lamp that produces white light. But we don't want all that light – just the blue part. So, we use an exciter filter to let only blue light through. This blue light is then directed onto the specimen. The fluorochrome-stained parts absorb this blue light and emit green light. A dichroic mirror helps in this process by reflecting the blue and letting the green light pass through. The green light then reaches our eyes or a camera, showing up against a dark background. Pretty cool, right?"