Is the visibility of standardized inflicted bruises improved by using an alternate (‘forensic’) light source?

•A weight was dropped onto the forearm of volunteers to create bruises.•Bruises were photographed using white and alternate light at 415nm.•Photographs were evaluated by 10 assessors independently.•Bruises were slightly better visible with alternate light at days 1 and 2.•No differences were found in bruises aged 0.25, 7 and 14days. To study the visibility of standardized inflicted bruises by using an alternate (‘forensic’) light source compared to a white light source. Bruises were inflicted on the flexor site of the forearm (halfway in the middle) in 76 adults, by suddenly allowing a cylindrical metal object (400g) with rounded edges to drop for 1m in a vertically positioned tube. At 0.25, 1, 2, 7 and 14days after this blunt force impact, the impact site on the forearm was photographed with a white light source and subsequently with an alternate light source at 415nm. Visibility of bruises on 170 randomized photographs was assessed on a calibrated monitor by 10 forensic medical specialists (physicians and pathologists) independently in two sessions: (1) with white light source photographs, and (2) after a mean of 11days with greyscale converted alternate light source photographs. Bruise visibility was expressed as a report mark between 1 (very bad) and 10 (excellent), or as ‘no visible bruise’. To determine intra-rater agreement, 10 of 170 photographs were assessed twice (untold to the assessors). In total 3600 (180×10×2) photographs were assessed. 39 of 73 (53%) participants who completed the study, developed a visible bruise (women more often than men, p