Abstract
Bruises are often difficult to detect on victims of violence, potentially impacting investigation and prosecution. The purpose of our randomized controlled trial was to measure the effectiveness of an alternate light source (ALS) within visible and long ultraviolet spectrums at improving bruise detection compared to white light over time. We also examined the effects of skin color, age, gender, localized fat, and injury mechanism on bruise detection. Participants included 157 healthy adults with balanced sampling across six skin color categories. Bruises were created under the controlled application of a paintball pellet and dropped weight to one upper and lower arm, respectively. Using a crossover design, both bruises were examined 21 times over 4 weeks. Ten different wavelength (350-535 nm) and filter (yellow, orange, red) combinations were used. Multilevel models were used to analyze 2903 examinations on both upper and lower arms. Results in multivariable models showed after controlling for other covariates 415 and 450 nm using a yellow filter had greater odds of detecting evidence of bruising than white light (Upper Arm: 415 nm: OR = 5.34, 95% CI: 4.35-6.56; 450 nm: OR = 4.08, 95% CI: 3.36-4.96). Under either light source, being female and having more localized fat had increased odds of detecting bruises created by the dropped weight (female: OR = 2.96, 95% CI: 2.37-3.70; fat: OR = 1.21, 95% CI: 1.09-1.34). Our results support ALS as an appropriate tool to enhance concurrent physical assessment of bruises in the presence of known history of injury. Future development and evaluation of clinical practice guidelines for ALS application are needed.

Bruising is one of the most common types of soft tissue injury noted on victims of violence, including intimate partner violence, sexual assault, child abuse, and vulnerable adult abuse. Such injuries are usually caused by blunt, compressive or squeezing force trauma resulting in damaged blood vessels. Evidence of bruising is usually identified by forensic clinicians through observed skin discoloration stemming from exsanguinated blood and its associated inflammation. Injuries, such as those from strangulation, can significantly impact clinical outcomes if they are not detected. Additionally, research indicates injury documentation is associated with greater victim engagement in the criminal justice process and may provide corroborative evidence in court.

Many factors contribute to being able to observe a bruise under normal lighting conditions, including the amount of extravasated blood; location on the body; depth; subject's age; bruise's age; and skin color. When blood is released into the extravascular space, hemoglobin is broken down through enzymatic processes to include bilirubin as one of its byproducts. On spectrophotometric analysis, hemoglobin exhibits the greatest amount of light absorption at a narrow peak of wavelengths around 415 nm, with a secondary, broader peak in light absorption around 543 and 576 nm. Bilirubin has a broad absorption peak around 460 nm. Gross observation of light absorption by these molecules requires the use of alternate light, specific wavelengths which may include the visible (400-700 nm) or long ultraviolet (290-400 nm) spectrums. Generally, light is reflected, transmitted, scattered, and/or absorbed by the skin's surface. Transmitted light can be absorbed and reflected by deeper structures, with longer wavelengths generally having greater skin penetration. Filters (e.g., colored goggles and camera lenses) can then be used to block the reflected light allowing the absorbed light to appear darker by comparison.

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