If you watch TV you've seen the Personal Alternate Light in use. A 400nm LED light provides lighting for locating body fluids and in crime scene fingerprint processing when using fluorescent powders.
Like other blue-light-emitting light sources used to visualize physical evidence and latent prints, it is necessary for the examiner to wear orange goggles which are included in the kit. Darken the room or area, shine the light at various surfaces where physical evidence might be found. Collect fluid and fiber evidence. Photograph fingerprint evidence with an orange filter on the camera lens.