We are moderate fans of Buffy the Vampire Slayer. I say 'moderate' because we do not have the complete series on tape, do not go to the conventions, do not have Sarah Michelle Gellar's biography off by heart and so on. But we watch fairly enthusiastically, despite one inconsistancy that has puzzled us (well, me) for some time.
(Yes, I am applying logic to film and TV fantasy again. Tiresome, isn't it?)
Buffy the Vampire Slayer, I should explain, is an American TV series about the eponymous Buffy, her friends, her life in high school and (now) college, and her night-time job fighting the forces of darkness. There is a spin-off series called Angel, about one of those forces of darkness who turned good, there is lots of gymnastic fighting and punching and kicking, in every episode of Buffy Gellar gets to look all girly and trembly-lipped at the camera at least once, and in every episode of Angel David B gets to take his shirt off to reveal a frankly amazing set of muscle delineations. The one-liners are good too. So, a top-range soap opera, combining what passes for Wildean whit in the 21st century, lots of bodies, and a nice, simple plotline about ever escalating forces of evil trying to take over the world.
In the first series, the vampires were numerous, only came out clothed in rags at the dead of night, and were dispatched with a minimum of screaming by the traditional method: five minutes desperate hand-to-hand fighting followed by a stake through the heart. But as the series developed, several of the vampires had characters placed on them by the plot-writers, and consequently became much better dressed, got better lines, and started to get better lighting. So much so that Spike and Angel can now walk around indoors during the hours of daylight without any trouble.
Which leads to a troubling conundrum. When vampires are exposed to sunlight (as anyone who has watched From Dusk to Dawn knows perfectly well), they burst into flames and explode. Thus it is in Buffy. I always thought this was chemical photosensitivity, and we can think of some perfectly sensible-sounding reasons why this would necessarily be so.
For example, humans achieve high levels of energy output by combining otherwise pretty stable molecules with oxygen to create rapid, vigorous chemistry for running, thinking, and eating more pizza. But vampires have no heartbeat, no way to get oxygen to the muscles (and brain, in the case of those with good lines).
So their biochemistry is radically altered to run on, say, TNT, which can give the same energy output but without O2. Most the nitrophenols are light-sensitive, so expose a vampire to enough UV and their biochemical reactions got into chain reaction and, whammo!. The incessant need for blood, and fresh blood at that, is probably because they need the reduced metabolites and antioxidants to damp down the spontaneous detonation of their own metabolism even in the dark. Note that where a vampire usually bites its victim, they would get the carotid veins, rather than arteries - they are after oxygen-free blood, all nicely reduced and ready to soak up those superoxide radicals.
(Apropos this chemistry, it has never made sense to me that Buffy does not actually use TNT to stop vampires. I know they have superhuman strength and recuperative powers, but being blown into tiny pieces would probably give even the toughest supernatural entity pause. But I digress.)
But even in series 1 of Buffy, we see Angel stalking the local nightclub, with UV striplights going full tilt, and nary a whiff of smoke. Indeed, ordinary strip-lights put out quite a bit of UV. So it is not UV per se that is out vampire-ignitor.
What about the sheer intensity of light? No, searchlights seem OK, but the diffuse sunlight of a cloudy day means barbecue time.
Maybe it is something in sunlight itself? The spectral distribution, the NIR content? Well, Angel seems pretty healthy in diffuse, reflected sunlight, even reflected off concrete and sand which reflect just about everything. So that is not it.
Basically, it is starting to look as if the reasons vampires explode in sunlight is that they are just so terminally cool that they would rather die than have suntans spoil their black-and-pale image.
But no, wait! There is one thing that scattered light does not have, but regular sunlight even diffused by clouds does, and that is polarization! Maybe it is polarised light that is the problem?
This leads to a whole new line of speculation, which also explains why you cannot see vampires in mirrors. What if, instead of TNT, vampires ran on perfectly ordinary biochemistry, but under huge steric strain? Their molecules are all violently twisted by the forces of darkness. Now, normal light will simply bounce off them, but circularly polarised light will interact specifically with those misshapen molecules and put additional strain on them, tweaking them past the point at which they are stable and converting them to a lot of free-flying atoms. Same effect as TNT, but different chemistry. (It must be circularly polarised light, as otherwise vampires would be fine outside if they kept at 90 degrees to the plane of polarisation, ie if they fell over.) This also explains how a vampire can turn a human into another vampire without requiring several kilos of sodium nitrate. Simply twist neck, bite, twist molecules, and you are off.
So circularly polarised light falling on vampires sets them off, but what of light reflected off them? This will be polarised all to hell and back. Light reflected off glass also picks in a polarization due to differential reflection - you can use stacked sheets of glass as polaroid sunglasses if you do not mind the 10kg weight and the inch-thick steel frames. So what about the highly twisted light coming off a vampire? I will have to check the geometry next time I meet one, but I suspect that if the light is polarised just right a mirror will reflect it pretty poorly, or maybe not at all. Vampire's inability to check their looks over in the shop before buying that really cool set of black, skin-tight jeans is not supernatural, it is just basic optics.
With two such devastatingly conclusive pieces of evidence in our floppy leather coat pocket, we can suggest two new strategies for Buffy and her friends.
Why wait for the sun? Lasers emit polarised light. No more wooden stake, hand-to-hand nonsense. A laser rifle at 500 meters will pick them off, just using the laser spot alone. I reckon all the vampires killed in the first three series could have been dispatched in a single episode with a passive, laser-based IR burglar detector system, and Buffy would never have had to get out of bed.
But that would not be much fun. Any other systematic circular perturbation of the hellish molecules should do the trick. Whirl a vampire round sufficiently fast, and they should go off. I would suggest the Walzers at a fairground. Strap 'em in and watch 'em blow! It would also be a good test for prospective fathers-in-law to run on their dear one's intended. Less fatal that a stake through the heart, and it could, under extreme circumstances, even be considered fun.
Look out for this plot twist in Series 17 of Buffy, together with how to kill
demons with the sharpened feet of a Zimmer frame made entirely of (chiral) cellulose.