Final answer:
Luminol is used to detect bloodstains by reacting with the iron in blood, producing a blue glow that's visible in low light, allowing forensic investigators to identify traces of blood that might not be seen otherwise.
Step-by-step explanation:
Luminol is a chemical that exhibits chemiluminescence, with a blue glow, when it reacts with the iron in hemoglobin, which is an essential component of blood. This reaction is used to detect bloodstains that are not visible to the normal eye. Forensic investigators spray a luminol solution over an area where blood evidence is suspected, even if the area has been cleaned or is not visually apparent.
In the presence of blood, luminol emits a blue glow which can be seen in low light conditions or with the use of special photographic equipment. Despite its sensitivity, it is important to note that luminol can also react with some other substances, potentially leading to false positives, so further confirmatory tests are usually conducted.