05 March 2010


Many moons ago, even unto the time of our forefathers ... well, it was in the 1970s, actually ... there was a long suffering young woman called Penny (to my shame, I am unable to recall her surname). She was a fabric designer, producing vivid sheets of pattern and colour which took on a life of their own as they moved.

At the same time, there was a USAmerican photographer (again, alas, I have forgotten and cannot now locate his name) who spent his time producing what he called "powerflics". These were photographic images of landscape painted at night by repeated multiple local electronic flash and by the headlights of vehicles driven around within the field of view. The result was a combination of pooled illumination on particular details and areas with lines of light which defined the contours of the ground in the dark areas.

Other influences combining at the same time: Barbara Hepworth (“moving through and over the West Riding landscape with my father in his car, the hills were sculptures; the roads defined the form”), stroboscopic flash, and (I had, at school not very long before, taken O-level Astronomy) visual fascination with the circular arc traces of stars during a long exposure.

As I have said before (ad nauseam, no doubt), art and science are for me only different ways of wondering at the same beauty of existence; photography and mathematics being my own particular ways in to them. Light painting and use of light traces are older than photography itself, but my interest was more specific than that. Both Hepworth's roads and the headlight traces in the powerflics partially described a surface under a wireframe mesh, poetically bringing together both strands. They also tapped into my concern with time as a dimension in still photographic images.

The upshot of all this was that Penny spent long night hours risking life and limb in the middle of busy road junctions as I explored this interaction of light, movement, form and time. (Why did she do this? She had no romantic interest in me. Perhaps she did occasionally get something useful to herself from my experiments. Mostly, I think, she was just a nice person, generous in her wish to help. I wish I could offer her the basic courtesy of remembering her full name.) We would fix lights and mirror fragments to her, and to swathes of her fabrics, and she would dance in the lights of passing cars. Heaven knows what the drivers of those cars thought; or why we were never interrupted by the police. The lights of the cars wove patterns around her, reflected from the mirrors, and also flared areas of the fabric into coruscating life. The lights moving with her and the fabric produced a tighter tangle of light trails within the outer shell, and smeared smaller, more subdued sweeps of fabric design through the darkness.

Fast forward thirty five years ... I'm interested in AcerOne's use of moving lights to mark out the locus traced by a moving skateboard (see also the earlier "Body flow" post) and, as a side result, to map the interaction of board rider with topography of ridden surface. Not on AcerOne's site are other images, previous experimental results leading up to those shown. In a comment to the "Jump Trails" post, I suggested flashing lights instead of, or as well as, constant ones. In response, AcerOne sent me the image of broken light trails descending a flight of steps (which I'm posting here, on the left; click for an enlarged view) with the comment that:

The previous week we had experimented with bike light and had set both the red and white/blue lights to flash mode. I actually disregarded those images as I didn't really feel like they capture the flow of body movement. Looking back on them though, they did make for interesting images, just perhaps not what I was attempting to achieve...

To an even greater extent than all those years ago, this use of light trails interests me under both my "photographer" and "mathematician" hats. A frequent concern these days, in a research communication context, is how to maximise the bandwidth of data visualisation without introducing confusion. Software designers put a lot of work into addressing this problem though development of visualisation packages such as, for example, OriginPro or Surfer. In this matter of photographic light trails, there are three main ways to differentiate between one line and another: intensity, colour, and texture.

The first, intensity, given the variation within a trace, has limited scope: a hard bright light like a car headlight can easily be distinguished from a dim diffuse one or from an illuminated surface trace, but fine distinctions are impractical – this being the price paid for very subtle and broad modulation bandwidth within each individual signal.

The second allows traces to be easily distinguished over roughly five colours (red, yellow, green, blue, and white). Although only red and white are readily purchased as strap on or clip on items, ready to go straight out of the box, white ones could easily be filtered (sweet wrappers over a torch serve the purpose in childhood games).

The third, texture, is obtained by rapidly interrupting the light source – that is, by making it flash. This option is provided on many wearable LED lights nowadays, and results in a broken line – the flashes and the gaps between them both lengthening as movement speed increases.

There is a fourth possibility, and that is use of either blurred conventional exposure traces as a slowly moving subject picks up ambient light (Penny and her fabrics, reflecting car and street lights, for instance) or sharp frozen renditions caught by one or more flashes during the exposure time (see, for instance, AcerOns'e earlier "Street light Dancing" post, or Gjon Mili's famous portraits of Pablo Picasso drawing in mid air).

In its simplest form, a flashing light is used alone (instead of a fixed one). This is what AcerOne has done in the flight of steps image shown here. The flashing can, however, also be combined with a steady light.

I discovered this by accident, when making long night exposures with the deliberate intention of combining an arc drawn by Venus with urban sodium lighting. During one of these exposures, an airliner flew across the frame. The steady navigation lights on the aircraft drew constant lines across the black of the sky while the flashing one added a precisely spaced set of brighter dots strung along the central line: an effect rather like beads on a wire (see the enlarged section of the image shown on the right). A similar effect could be obtained in AcerOne's context by strapping both steady and flashing lights next to each other on the same wrist or ankle – and emphaised, perhaps, by choosing white for the steady light and red for the flashing one (or vice versa).

I am, currently, working on persuading AcerOne to carry out this experiment for me. If that fails, I shall have to do it myself. I don't have his ready supply of skateboarding acquaintances, so I may have to go out and bribe or bully some children into assisting me ... unless, of course ... I wonder what Penny is doing these days...?

  • Extracts from Barbara Hepworth, A Pictorial Autobiography, Bath 1971 and London, 1985: Tate Gallery.


Julie Heyward said...

I think it would be cool (or maybe even *more* cool; what you have described is already very cool) to attach tiny strobes to the board riders' hands. That would go off repeatedly (how often?) and so you'd get little fluttery images of disembodied hands frozen next to the light track.

I know just enough about strobes (actually, I know nothing at all) to guess that strobes *on* the hands would create completely uneven lighting even if you could dial them down enough not to spread to the rest of the person. My imaginary strobes, of course, do just as I wish.

Felix said...

I very much like your idea, Julie.

Could you see your way to loaning me your imaginary mini strobes for some experiments next weekend? (Assuming I can find some imaginary skateboarders in time!)