On quality of light

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‘Quality of light’ is one of those phrases I use often, but perhaps should explain a little better. Similarly, we are all guilty of overusing the ‘good light/bad light’ phrase; but what does it (and we) actually mean? To a certain degree, we photographers are programmed both with preconceptions of what constitutes favourable light – based on our own or others’ historical work – and what constitutes ‘bad’ light. At the same time, we also have our own aesthetic biases and preferences – some of us may prefer flatter or more diffuse light as a consequence of spend childhoods at extreme latitudes, or be predisposed towards hard contrast because we’re tropical people. Here’s the kicker, though: I believe there is no such thing as truly bad or wrong light; there is only suitability for a given subject and set of aesthetic preferences.

I think the easiest way to decompose this is to break light down into its four qualitative components: intensity, directionality, color and spread. (If I’ve missed one, please feel free to chip in in the comments.) Let’s define them individually first, so we have a common understanding to start from:

quality of light-intensity

Intensity is a proxy for contrast: how bright is your source, and thus how bright is it relative to the other ambient sources? The more intense a source, the stronger the shadows it will produce immediately behind it, and the greater the contrast between the lit face and the shadow face of that object. When the source is so intense and the contrast so strong it exceeds the dynamic range of the camera, parts of the scene will clip to white or black – this can be a pain if your intention is to depict all parts of the subject clearly, but it can also be of artistic value if you want to choose to hide or obscure certain elements.

quality of light-directionality

Directionality describes diffusion: where is the light coming from? A point source is directional because all rays must emanate from that one point; a collimated source (e.g. slit or hole mask in front of a point source) is even more strongly directional because only light travelling in that single direction defined by the mask is allowed to pass through. In practical situations, a collimated source might be sun/clear sky shining directly through a window aperture or slatted blinds; projected shadows are strong and directionality is hard, strong or tight (your choice of descriptor). A diffuse, omnidirectional source could be an array of point sources behind diffusion material – neighbouring sources in the array make up for the single source’s single directionality, and the diffusion material forces further averaging. There is directionality, but effectively every point on the diffusion material facing the subject radiates 180deg in front of it.

quality of light-diffusion

Note: all light diffuses – and thus weakens – over distance; in a perfect vacuum this is not the case, but even interstellar space contains a few molecules of hydrogen or the occasional stray helium atom, which over millions of light-years is enough to create diffusion. The effect is obviously much faster in denser materials. Effectively, diffusion is the physical scattering of light by the medium.

quality of light-spread

Spread defines the width covered by the beam – it’s related to but not quite the same as directionality, because you can have a source that’s near to your subject and narrow, which results in a directional spot (and possibly high intensity if there are no other secondary sources) – or the same source could be wide and cover more of the scene. Thirdly, you could have a distant source that’s narrow but covers all of your subject anyway because of distance, angles and diffusion of the medium. (The four possibility of far/wide is no different to the third from the point of view of both the subject and the nearer camera.)

Color is pretty self explanatory: what is the dominant spectrum? Color of inbound light also of course affects color of outbound reflected light from a subject: the surface of any subject acts as a filter, absorbing some wavelengths and reflecting others. This is of course why subjects are not monochrome under white light – the nature of the material determines what is absorbed and what is reflected. If your inbound light is a wavelength that is absorbed by your subject, reflected light will be minimal and the subject will in turn appear dark – e.g. blue objects under red light and vice versa.

quality of light-one source

Even in scenes that have ostensibly only one source – say outdoors, daylight and the sun – that’s not entirely true. Every material on Earth is reflective to some degree, otherwise there’s no way we can see it. This creates some complexity because that means every surface is a source; fortunately, most of the time the surfaces are so rough and diffuse that the net output is fairly uniform and doesn’t really create clear secondary sources (and accompanying shadows). There is always some reflect light, somewhere. Even the atmosphere itself creates diffusion – think about fog, incense, smoke etc. For the purposes of photography, whether we worry about a source or not is determined simply by this: does it create a shadow? I believe the most important thing is to have a clear hierarchy of sources: you need to know where your key light is, and fill the rest (or make sure it’s filled for you).

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Impossible light – the sun was the only source, but there were plenty of ambient reflectors…

Shadows are the only way we can project three dimensions into two and imply some semblance of spatial order; at larger scales, shadows tell us what is in front of and on top of what. They create foreground-background relationships. At the micro scale, shadows create texture – without micro shadows, you can’t tell if a surface is rough or smooth. Reflective surfaces appear reflective because there are no shadows (and thus no diffusion), which means you see what’s immediately in front of that surface – governed by the rules of reflection, of course. Reflections can be interesting: multiple apparent sources without much loss in brightness even though you only have one true primary source; skyscraper corridors in modern cities are a good example of this – it’s possible to have a subject lit from all sides thanks to all that mirrored glass.

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Traditionally, I think when we say ‘good light’ what we really mean to say is that there is directionality, narrow spread and a good intensity differential; i.e. contrast and shadows. When there is ‘bad light’ or ‘no light’, we mean there is too much diffusion and thus no differentiation in intensity – no shadows. However, three scenarios come to mind here: firstly, in a situation where you are in full control of all sources – i.e. fast enough shutter or bright enough light to eliminate ambient – then you can really determine where light falls using positioning and modifiers. The second scenario is where the quality of light suits the subject: a clean, modern urban environment may look its best – or most aesthetically pleasing, at any rate – in hard directional light of morning or evening with clear skies; a portrait of an older lady requires a bit more diffusion, but still directionality. If you swap light and subject – diffusion in the urban scene and hard directionality on the lady – the aesthetics aren’t so well suited to the subject.

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I’m going to leave you with the third scenario: ‘no light’. In a heavily overcast outdoor situation – think London in winter – there are ostensibly no shadows, but this does not mean no directionality. In a way, you can always ‘force’ it – work at the extreme ends of the day just before sunrise and sunset; at night with artificial light; or if you can move the subject, use archways and porticoes because you will then only have a diffuse source from one side only – which is ideal for many kinds of work because it’s the sort of flattering light that hides flaws. Lastly, there’s also the option to throw spatial arrangement out of the window altogether: just as we can use strong shadows to blur the line between real and projected, we can use an absence of shadows to do the same; I think of it as painterly light 🙂 MT

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Comments

  1. Nice article. The last shot has very elegant lighting. Personally, I like the contrasty back lighting as in the picture of two men walking along.

    You do need to work on your drawing. That cloud is a disgrace. 😉

    PS I enjoyed the Hasselblad video. Very clear and civilised speech.

  2. I don’t think this is the best or even an accurate description of light quality. A wide spread is a property of some physical light source but has very little to do with the quality of light in a photographic sense. Place an object some distance away from a single light source. Now flag the object on both sides. Nothing has changed even though the effective “spread” of the light has been modified.

    Soft/hard light can be described as apparent size of light source compared to the object being lit. Sun huge as it is, small apparent size, effectively a point light source, hard shadows. 6′ softbox at arms length, large apparent size, soft shadows. Overcast day, entire sky is a huge diffuse light source, no shadows.

    • By flagging it, you’re effectively changing the size of the source.

      Soft/hard: in both situations, there is intermediate diffusion material between source and subject that’s changing the direction of light. From your point source, rays travel mostly in a direction directly between source and subject, which creates the projected shadow. This is not the case with soft box and overcast sky; light is scattered from every direction and the shadows are filled in (or not present).

      • I like the simple yet powerful description found in Light Science and Magic. There is basically color, contrast and brightness. Color is color. Contrast is what you describe as directionality. Your intensity is relative brightness but you describe that in terms of contrast. So while I understand what you mean it could be clearer.

  3. jean pierre (pete) guaron says:

    Thanks for this article, Ming – light is basic to photography, and this is one of the most interesting and thoughtful articles I have seen on this subject. Not just the article itself, but also your replies to the various comments on it.

  4. richard majchrzak says:

    …and of course that stonewall in the meadows is phenomenal. first glance the rays looked like illusional green sky , (photo-) graphical illusion….blink, blink , where am I ….

  5. I like light with a smooth gradient in intensity as a function of incident angle. Something you get with a very large light source (very large compared to the subject and camera-to-subject distance). The largest light source of this kind you can get is just before sunrise or just after sunset on a clear day. Your last image in this article shows such light to a good degree.

  6. Say, if you want to give up sleep altogether to make time for it, your final sketch shows definite potential as a New Yorker cartoonist.

  7. Great idea for a write up Ming endless possible lighting situations exist for follow up articles. With your ability to show and tell the subtleties of light fall on the same subjects this could prove to be a very important read. Peter coulson has a unique approach using the fall off of light from a modifier in a way most never think of, Ansel tried to shoot the silver light returning from a cloud back to objects on earth, please continue with this study.

    By the way just returned from Hong Kong labs are resurging there and film is being exposed by the Hong Kong photographers in a major way. Maybe because there is also a larger abundance of used film camera for sale at affordable prices and one can put a stellar shooting kit together for very little money. Although it brought back fond memories I shutter the thoughts of returning to those days. That being said with what I believe to know about my knowledge making a image now at 63 vs what I thought I knew when I was 18 I sure it would be less of a guessing game (imagine if I had the learning possibilities with the internet when I started shooting).

    Ming you could also include the air quality in your next follow up article which has an amazing effect on the image, I happened to make a panoramic image a year ago in Yosemite after seeing the images from that shoot I was perplexed as to why this one image jumps. I certainly had no thoughts of air quality at the time I was making it but by far it has better clarity, color, contrast and draw then any other image I made in the three day trip!

    • All of photography is in reality a study of light…too bad many make it a study of cameras 🙂

      As for film – I like the consistency of my results too much to go back, though as you said: we could do so, with better output than before. The workflow would still land up being at least partially digital, which to me defeats the point since it’s really the worst of both worlds.

      Air quality: good idea. I agree with you that it not only makes a huge difference to perceived pop and clarity, but also mood. And there are some parts of the world that just have much better air quality (and light!) than others…

  8. Bill Walter says:

    Good article on an important subject. There are several situations where I consider a cloudy day as a blessing. Certainly for portraits. The best portraits I’ve taken are on cloudy days and there’s much less work in post. The other scenario is when photographing flowers. I get tired of seeing photos posted of flowers with blown out highlights. Although an occasional backlit shot can be nice, but I prefer some filtering from clouds. On the other hand, I do prefer a sunny day for architecture.

    Ming… I really like your last shot as the lighting seems ideal. It’s a great example of “painterly light”.

    • Thanks. Diffuse directionality is generally safe, yes. Blown highlights in flowers are almost certainly because the photographer has failed to take into account clipping of individual channels.

      Sadly, even though this is an important subject – it’s received perhaps 1/4 the traffic of the Photokina analysis, which is in itself a comment on the general state of photography…

  9. Awesome tutorial Ming, thanks for sharing.

  10. richard majchrzak says:

    that first one….that’s a shot and more…stunner

  11. Excellent.

    I was thinking that photographing at skate parks in California, I live and die by the shadows and hard light. In nearby San Francisco Bay Area, the fog is often an impediment but can also be a companion.

    • I think I only had fog one morning during the total 4 or so weeks I spent in SF over several seasons – I admit I was somewhat disappointed… :p

      Almost every image I’ve seen from LA with available light has a certain quality to it though – I suspect a mix of light off the ocean and a thin warm filter of pollution…

      • You didn’t see the brown cloud hanging over LA? It’s much smaller than in the 1960s but is still there. Even at Santa Monica, LA County, things don’t seem so bad but then, that is at the ocean.

        If you follow KarlTheFog on Twitter, you’ll know when you’ll get shots with fog. Driving across the Golden Gate Bridge with fog is not amazing, but disturbing. However, the photos from the Fort Point area are incredible. Right now, is a good time as we get closer to the rainy season.

        • I did – but you must remember that I’m from a city that a) sits in a valley, b) pollutes just as badly, and c) sits under the wind path of Indonesia’s burning forests. We have months of the year where visibility is less than 300m because of the haze. Sadly this is not water vapour but carcinogenic combustion products, so one really doesn’t want to be out photographing in that soup.

  12. Excellent tutorial. Thank you. I’ve passed the link on to my students.

  13. All of the above is true. But I think, the subjective aestethics play a huge part. I have spent two years (of a total of six) in a photographic factory, pre setting colour filtering for the workers producing positive prints from film exposed by portrait photographers all over the country (roughly four thousand professionals). And their preferences as to what a “good” or “healthy” skin tone is, differed a lot. This was back in Austria some thirty years ago, Austria being a tiny country, there were big regional differences. Overall, I still remember the province Carinthia liking rather red skin tones, Styria a mixture of red and yellow, to the north-east, Burgenland and Vienna, lots of cyan had to be added, thus producing much “colder” tones of skin. All of those portraits were well lit in a studio by professionals and yet one never got through with just neutral colouring stipulated by densitometric measurements, but had to take the personal preferences of the customers into account. Not after having to learn this first by trial and error (errors meaning costly customer protests).

    • It’s nice to hear that level of service existed/exists. No such luck in my part of the world – the lab’s first response here is to blame the customer!

      But yes, aesthetics play a huge role in color temp, at least. Shadows remain shadows though…

      • Well, that was back at a time, the lab was able to charge good money for the prints – also long gone. But I know of some companies still offering such services (at some cost, though). Whereas on the large, machines have taken over, where professional labs haven’t been forced out of business completely with the rise of one-hour-automated developing gear on every corner. The factory I worked in once employed 250 people and was closed some fifteen years ago, long after I had left. We ran an overnight pick-up and delivery service all over the country. And we had divisions dealing with professional photography only. Everybody working there were trained photographers like me. This kind of explains the service but also the cost.

        • I think most serious people would see the value in doing it once and getting it right the first time, and consistent thereafter. In the long run it works out cheaper anyway. Sometimes I wonder what it would be like to live in a country where everything isn’t a patch job – you cannot sell quality to people who simply do not care…

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  1. […] often talk about the painterly qualities of an image, but without the right quality of light, and to some extent, subject matter – it isn’t possible to create the same controlled […]

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