Luminol is often used to detect latent bloodstains at crime scenes. Several formulations of luminol-based solutions are available. These formulations must be compared and assessed for their efficiency for use at crime scenes. Most studies consider spectrometric measurements, where the reaction is triggered and monitored in spectrometric cells. In spectrometric cells, the blood is liquid, and the luminol is mixed with the blood, not sprayed onto it. Conclusions made from spectrometric measurements may not be accurately transposed to the situations of luminescence encountered under crime scene conditions because the testing conditions do not replicate the crime scene. This study consequently proposes a photographic-based method for measuring the chemiluminescence from bloodstains sprayed with luminol.
The photographs that were made during the current experiments were converted into grayscale to provide objective values of the intensity of the chemiluminescence, which was recorded every 5 seconds during a period of 10 minutes. This photographic protocol was used to record both the regular luminol solution and also the luminol-fluorescein mixture. Results showed that the proposed method can objectively quantify the chemiluminescence intensity. Furthermore, contrary to what previous research that was based on spectrometric laboratory measurements indicated, the luminol-fluorescein mixture was not more efficient than a regular luminol solution. Differences may be explained by the measurement strategy (spectrometric measurement versus photographic recording), the proposed approach being more representative of the way luminol enhances bloodstains at crime scenes.