Tag Archives: reflection

albedo

Look at these trees. They exhibit a pleasing play of shadow and light: shadows on the right side, light on the left – a nice moderate light, glowing.

Now look at the buildings behind them. Look at where the light is. Look at the direction the shadows are going in.

The sun is to the right. South-southwest. This is Bryant Park in New York on an October afternoon, and we are facing east-southeast toward the New York Public Library (remember, Manhattan is not truly north-south). The bright side of the trees is the one away from the sun. The direct sunlight is blocked by buildings on the right: just shadows there. The soft glow is thanks to light reflected from buildings on the left.

When I first stopped to think about that fact – how the bright side of the trees was from reflected light – I thought something like “Well, I’ll be…”

I’ll be what? I’ll be doggoned? No. Albedo.

Albedo. Take a moment to reflect on that word. It takes all its time to reflect on you… and on everything else. And from everything. You included.

The sun gives light: as it burns it releases photons. If you stand in the sun, you stand in the path of a small, small wedge of those photons. They don’t make it through you. Some are absorbed; some bounce back off. The number and nature of those photons bounced back depends on the colour of your skin and clothes. If you are wearing a blue shirt, it keeps most of the photons that aren’t blue, and bounces back – gives away – more of the blue ones. This is how we have colour: surfaces keep the colours they don’t show and give away the ones they do show.

Meanwhile, the space behind you, including the back of your head, is not in utter darkness; it is lit by photons reflected off other surfaces – and diffused by bouncing on molecules in the atmosphere.

Albedo is the percentage of light a surface gives away – doesn’t keep. A surface that kept all the light would have an albedo of 0 and would be perfectly black; a surface that reflected it all would have an albedo of 1 (i.e., 100%). The reflection can be directional – as with a mirror – or diffuse – as with paper. Highly reflective but not perfectly flat or even surfaces give a mottled light.

The word comes from Latin albedo ‘whiteness’, from albus ‘white’. You will recognize the root from abumin and albino and Albus Dumbledore (which, in full, means ‘white bumblebee’). Albedo was first applied to the reflectivity of surfaces by Johann Heinrich Lambert in 1790. An important current usage is to refer specifically to the reflectivity of celestial bodies – such as the earth.

It is also important for environmental science. Snow, for instance, has a high albedo, but once it starts melting and the water runs away, more and more dirt and dark matter is left, giving a lower and lower albedo, which means it absorbs more and more solar radiation and melts faster and faster. The glaciers of Greenland are currently demonstrating this, and it is a matter of some concern. It becomes an accelerating self-destructive cycle of selfishness, as it were.

Separate albedo can be calculated for each wavelength. Some people have suggested that since a blue surface keeps the light that is not blue and gives away the light that is blue, its real nature is not blue. I do not agree. As you go through life, you receive love and hurt, joy and anger, comfort and pain; you do not give all of it back to the world, but only those things that you wish others to receive. A person who receives hurt and joy but gives only joy to others is not a person whose nature is hurt. We do what we want to do and what we are able to do. Our character is our able-do; it is our albedo.

And in the darkest moments of our life, when the sun seems blotted out, there is still light: the albedo of others.

reflection

We do so many things by reflex these days, and so seldom pause for reflection. We are too often too likely to view things through a single lens, and not to put them in perspective.

Let us reflect on reflection. The word reflection is formed by derivation (not inflection) from reflect, which comes from Latin re plus flectere ‘bend’: a reflection bends – or bounces – light back. A mirror is, semiotically, as Umberto Eco has explained, a prosthesis, not a sign in itself. Any object that reflects does not contain the image it reflects; what you see in it depends on your position. The reflection of a tower in a pool of water is just your line of sight reflecting to the tower in that position, and seeing the tower scattering light that was scattered onto it from countless molecules of atmosphere and surrounding matter, starting at some point with the sun: a myriad of reflections. That glowing glass building shining with the sun only shines it there for you because your line of sight bounces off it at that point towards the sun. The sun’s rays are bouncing equally off all parts of the building that face it; every square metre is glowing brightly for some eye in some location, but you only see the part that glows for your position. Reflection may lead to illumination, but what is illuminated depends entirely on your personal viewpoint.

Which is your personal perspective, of course. Perspective is simply a geometrical consequence of a single point (an eye or other lens) gathering reflected light from all around, and interpreting the diverging (or converging) lines of sight as parallel. It helps us gain a sense of the relative size of things, but what helps even more is binocular vision: add a second eye and the lines of sight converge slightly differently, and allow depth perception. When we talk about putting things in perspective, we really ought to talk about putting them in parallax.

Parallax is how a rangefinder camera – such as a Leica M-series camera, or the Ricoh that was my first camera – allows the user to focus: you line up two images at the point you want in focus, as your eyes do. On the other hand, an SLR allows through-the-lens focusing: the image bounces off a mirror onto a screen that is the same distance from the lens as the film or sensor, and you see on the screen what is in focus. This is why it’s an SLR: single-lens reflex. Reflex because the light reflects. Off the mirror.

That’s not a joke or a pun; that’s what the word reflex means: bounce-back. Some stimulus affects your nerves; you give a response automatically, like a mirror – or those Newton balls. Tack, tack; tack, tack; tack, tack…

I don’t use an SLR anymore (though I do have one). I don’t usually use a rangefinder camera, either (though I do have one). I use a camera (two of them, in fact) that shows on a screen on the back the image that is striking the sensor. This makes it smaller and lighter – quieter too (the mirror doesn’t have to flip up and down). It also means I don’t have to hold it up to my eye. Which is good because I wear glasses, but also good because when you hold a camera to your eye people react to it: they see your specular act with the prosthetic of the camera and they flinch, or turn away, or stare, or grin senselessly. The act of seeing is presented as not a passive reception but an active taking, and there is a reflex response to that.

When I hold a mirrorless camera at waist or chest level, especially a smallish one, it simply receives; few people take any notice of it. But it is still a prosthetic for my eyes, a single-lensed prosthetic giving me a different perspective from what my eyes see – different because lower, but also because it has a different angle of view, wider or narrower depending on the lens. I see things not just in perspective (as one always does) but from a different perspective. I see reflections – light bounced once or many times from its source or sources (and at night there are so many sources!), objects showing their positions because they reflect not smoothly but roughly, diffusing, scattering the light that comes to them, and shiny objects that do reflect smoothly, letting my position dictate what I see. You must know the position of what is being reflected before you can know with certainty the position of the reflector… unless there are points of opacity and diffusion on the reflector, which will allow your parallax to fix them.

When we pause for reflection, we do so to become more aware of our position and the positions of others. We do it to stop acting by reflex. Which means that, really, we pause for diffusion. And to put things in parallax, or at least to see them through another lens.