The importance of dark adaptation for forensic examinations; an evaluation of the Crime-lite Eye

Forensic practitioners are recommended to dark adapt their eyes prior to conducting evidential searches in the dark. The dark adaptation process remains poorly standardised across the discipline, with little quantified regarding the benefits of such preparative steps. Herein, we report the findings of a study that recruited 50 participants to assess the effectiveness of the Crime-lite Eye™, a darkness adaptation device developed to assist forensic practitioners both in the laboratory and in field. Participants were tasked with searching for the fluorescent signatures left by reaction of 1,8-diazafluoren-9-one (DFO) with amino acids, in a manner akin to the fluorogenic fingerprint treatment of porous evidence. Using an Epson Stylus Photo R265 inkjet printer, ink cartridges were filled with alanine solutions of various concentrations, allowing different motifs to be printed onto copy paper and subsequently developed using DFO. Participants searched for this ‘evidence’ both with and without dark adapted vision. On average, participants were able to locate and correctly recognise 16% more evidence once dark adapted using the Crime-lite Eye™. The increase in evidence located by participants once dark adapted suggests that crime scene officers should be dark adapting in order to visualise as much as possible. The time taken to dark adapt, 10 min on average during this study, is not excessively long, and should not significantly slow the investigation. •Inkjet printed alanine shapes were produced using a standard inkjet printer.•These alanine shapes produced consistent fluorescent marks when treated with DFO.•Dark adapting the eyes can increase the amount of fluorescent evidence found.•Dark adaptation allows fluorescent evidence to be more accurately observed.•The Crime-lite Eye™ is a viable method to obtain a known level of dark adaptation.