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Alternative Light Sources and Their Effectiveness in Enhancing the Visibility of Injuries

History of ALS

A fairly new science has emerged within the past 70 years regarding the use of alternative light sources (ALS) to enhance the visibility of injuries, being used in forensics starting around 1990. There has been research done on this topic, however, it hasn’t been extensive and has only recently been done with regards to how skin color effects the results. Various confounding factors must also be taken into consideration such as pre-existing skin conditions and topical products such as makeup or sunscreen, as they could mimic bruising by producing absorption under alternate light. In both the living and the deceased victim of violence, it is essential that injuries be examined adequately in order to properly reconstruct the crime and completely document all injuries.

The use of reflective ultraviolet radiation and infrared-aided photography have both been used to improve the visibility of old injuries, and this use has been well documented and explored. One downside is that exposure to UV light is harmful to both humans and to trace DNA evidence. Another downside is that these wavelengths are not visible to the naked eye and are only visible after photographs are taken using filters that block all light passing through the lens except for the light of interest.

Bruising in forensics

Bruising is a very common injury in victims of violent crimes such as sexual assault, child abuse, vulnerable adult abuse, intimate partner abuse, and even murder. Evaluation of these bruises can help differentiate between accidental and non-accidental causes. Bruises cause discoloration of the skin due to the injury to the blood vessels underneath the skin and in the past was dated by color. However, it is now felt that bruising cannot be effectively dated by its color. In addition, some injuries may not be visible at the skin surface because they are too recent. Therefore, how can a forensic clinician effectively detect and date these injuries in order to impact both clinical and criminal justice outcomes?


Using ALS to evaluate bruises

Under normal lighting conditions, many factors contribute to whether or not a bruise can be detected including where the bruise is located on the body, how deep the bruise is, how old the victim is, how old the bruise is, the sex of the victim, how much localized fat is in the area of the injury, what caused the injury, and what color the victim’s skin is.

To understand this, we must understand how spectrophotometric analysis is used, which substances in the body absorb light, and at what peak. When someone has an injury that does not break the skin’s surface, such as a bruise, blood is released into the spaces around the blood vessels known as the extravascular space. One of the components of blood, hemoglobin, breaks down and another substance, bilirubin, is a byproduct. Hemoglobin absorbs the most light at an initial narrow peak wavelength of 415 nm and a second broader peak wavelength of 543 nm and 576 nm. Bilirubin absorbs light broadly with a 460 nm wavelength peak. But to observe these wavelengths an alternative light source such as those which are visible to the naked eye (380-740 nm) or long ultraviolet (290-400 nm) spectrums must be used. Visible light falls between infrared and ultraviolet on the electromagnetic spectrum. The skin’s surface usually either reflects, transmits, scatters, or absorbs light. Deeper structures under the skin can absorb transmitted light with longer wavelengths being able to penetrate more. Filters such as goggles or a camera lens can filter or block the reflected light thus allowing the absorbed light to appear darker. However, melanin in the skin that creates our skin color has an absorption spectrum that overlaps hemoglobin thus further compounding this issue for darker skinned individuals.

In order to avoid the dangers of ultraviolet light, visible light (380-740 nm) could be used. When the skin is exposed to narrow-banded visible light, some of it is reflected and some is absorbed resulting in a fluorescence of the skin. Since the hemoglobin and bilirubin in the injured tissue absorb light and are almost non-fluorescent, the difference in the normal skin fluorescence and the traumatized skin enables the injury to be perceived as a dark area within the surrounding non-injured skin.


Studies on ALS

One study by Scafide, et al, was done in 2020 regarding skin color. The conclusion was that an alternative light source with “wavelengths consistent with hemoglobin absorption, 415 and 450 nm viewed through a yellow filter, provided five times greater odds of detecting bruises than white light.” Their study supported findings from previous studies, however, they did suggest that evidence-based clinical practice guidelines for alternative light source usage needs to be developed and evaluated.

A study by Nijs, et al, in 2019 studied the visibility of bruises by using an alternative light source at 415 nm compared to a white light source and concluded that bruises inflicted by standardized blunt force impact were only slightly more visible with the alternative light source than with the white light after 1 and 2 days, but not after 0.25, 7, and 14 days. Therefore, they felt the value of improved imaging was limited.

Trefan, et al, in 2018 compared conventional, cross polarized, infrared, and ultraviolet imaging when assessing childhood bruising. They concluded that bruises of low contrast in living children can be delineated and reliably measured using conventional and cross-polarized imaging; and the size of a bruise can be defined by conventional, cross polarized, and ultraviolet imaging using computer software. However, the study was limited in that they only studied bruises of the same age in the four modalities and therefore did not evaluate whether or not the infrared and ultraviolet imaging could extend visibility over a longer period of time.

Another study by Limmen in 2013 studied how the various colors and wavelengths of “Crime-lites” improved visibility of injuries. These lights are violet (400-430 nm), blue (430-470 nm), blue/green (460-510) and green (500-550). In this study, the violet and the blue were the most helpful in improving the visibility of injuries that were barely visible and non-visible to the naked eye.

Author Filter/Color Wavelength Conclusions
Scafilde, et. al (2020) yellow filter 415-450
  • 5x greater odds of detecting bruises
Nils, et. al (2019) n/a 415
  • Only slightly more visible after 1 & 2 days
  • No change at 0.25, 7 and 14 days


violet and blue 400-430 and 430-470
  • Violet and blue were most helpful in improving visibility


In summary, the use of alternative light sources in identifying bruises is still an emerging science showing great promise in the field of forensics. However, there are limitations to the research that is currently available, and a standard practice has not yet been developed. Further research is needed and more in-depth training of persons using the technology is required.



Limmen, R., Ceelen, M., Reijnders, U., Stomp, S., de Keijzer, K., & Das, K. (2013, March). Enhancing the Visibility of Injuries with Narrow-Banded Beams of Light within the Visible Light Spectrum. Journal of Forensic Sciens, 58(2), 518-522. doi:10.1111/1556-4029.12042

Nijs, H., De Groot, R., Van Velthoven, M., & Stoel, R. (2019). Is the visibility of standardized inflicted bruises improved by using an alternate (‘forensic’) light source? Forensic Science International, 294, 34-38. doi:

Scafide, K., Sheridan, D., Downing, N., & Hayat, M. (2020, July). Detection of Inflicted Bruises by Alternate Light: Results of a Randomized Controlled Trial. Journal of Forensic Sciences, 6(4), 1191-1198. doi:10.1111/1556-4029.14294

Trefan, Harris, C., Evans, S., Nuttal, D., Maguire, S., & Kemp, A. M. (2018). A comparison of four different imaging modalities – Conventional, cross polarized, infra-red, and ultra-violet in the assessment of childhood bruising. Journal of Forensic and Legal Medicine, 59, 30-35. doi:



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