Of all the creature’s weaknesses, a vampire’s incapacity to withstand exposure to ultraviolet (UV) light is the most noteworthy. All members of the vampire species suffer from an extreme form of xeroderma pigmentosum – the inability to repair cellular damage caused by exposure to UV radiation. Any protracted exposure to UV light will set off a chemical reaction that causes the creature’s exposed epidermal layer to oxidize and combust within a matter of seconds. Based on recorded empirical data, the following timing sequence occurs during a vampire’s exposure to UV light:
- 1–10 seconds: third-degree burns
- 10–20 seconds: spontaneous combustion
- 30+ seconds: full immolation
While the specific activators that cause this violent reaction have yet to be analyzed, it is apparent that UV light has a powerful effect on the undead species. It is surmised that the reaction is similar to the use of light to eliminate bacteria and as a disinfecting germicidal agent—albeit in a much more powerful context. Whatever the reason for this reaction, this liability not only enables a human combatant to leverage a powerful ally in the warming rays of the earth’s sun; it also keeps the undead at bay for roughly half the operating day, allowing humans to go about business in broad daylight with little concern of being attacked by a voracious ghoul.
However, it is not only direct exposure to the sun’s ultraviolet rays that make the daylight hours a liability for the undead. A vampire’s biorhythm, its physical clock cycle, seems to be directly tied to the rising and setting of earth’s heat source. Thus, a vampire’s physical advantages seem to ebb and flow as the hours pass from sunset until sunrise. It comes as no surprise, then, that most vampire attacks occur between the hours of midnight and three a.m., when the creature’s physical biorhythm is at its peak. Conversely, a vampire will grow increasingly vulnerable closer to the hours of sunrise as its physical cycle begins to wane. The creature is at its weakest when the sun’s ultraviolet rays are at their peak, approximately twelve p.m. to three p.m. Understanding the creature’s physical cycles can help you ascertain your level of vulnerability during a combat entanglement with the undead.
While the rays of the sun are the most obvious source of UV light, they are not the only source. Due to the growing popularity of indoor gardening, many artificial sources of ultraviolet light are now available to the public in the forms of fabricated lamps, beams, and light bulbs. These sources can be just as effective as the light of the sun, if not more so due to their portability. Be cautious in their use, as exposure to UV light through these portable devices can be as damaging to a human’s skin and eyes as the rays of the sun. They are also notoriously fragile; wielding such a device in the heat of vampire combat will in most cases cause your opponent to shatter the light source before mounting its counterattack.