The Quality of Light
By Robert L= ay
Released 15= April 2009
In order to better understand the "quality of light" as it will be discussed here, I believe we must approach it from the perspective of "effect" or "result" and not from the perspective of a clinical1 study of what makes up the light itse= lf or of what characteristics it is comprised2. This "effect&q= uot; or "result" approach will become clearer once we introduce some specific examples of the difference between the source and nature of light itself and the effect it has upon the various elements of a photographic sc= ene.
Our camera and the photographic process cannot know fr= om where the light comes or how it is generated. Our camera and its sensor can only record the "results" or "effects" of the lighting = as will be recorded in the virtual5 photographic image. There are infinite ways in which l= ight can be generated, many of which will produce the identical effect or result= . In other words, the final result= or effect = ;of the lighting on the image is all we are really concerned about - not how= the light itself was generated.
In this article our emphasis will be on recognizing the various qualities or characteris= tics of the illumination of our scene as they affect our artistic objectives. As= a consequence, this article will not discuss in detail any flas= h or strobe devices nor any “studio lights” as are typically found in portrait studios. The hardware approach may indeed be important to those who are in the business of producing illumination devices or devices that manipulate or modify the light, but we are more concerned with the result a= nd the effect. Likewise, we will discuss the effect of reflectors and diffuser= s, as they effect the resulting photographic image = without going into any details of their design or manufacture.
The lighting we will discuss for outdoor scenes is tha= t from the sun, sky, electronic flash, reflectors and diffusers, either individual= ly or combined. We will be particularly interested in a lighting environment k= nown as Open Shade.
Shadows are the best indicator of contrast. When shado= ws are not present, or are very faint, it indicates that the captured scene will b= e relatively low in contrast. This condition is typical of a heavy overcast sky with the= sun totally obscured and no deep blue sky or white clouds.
Conversely, when there are distinct black shadows in t= he scene, it indicates that scene contrast will be relatively high. This condi= tion is typical of a bright sunny day with deep blue sky and little or no clouds= . Distinct shadows do not exist in a scene with soft, diffuse lighting.
Every possible combination of sun, clouds, blue sky and overcast produces a different value of contrast in the scene, and that cont= rast will be indicated by the deepness of the shadows in relation to the highlig= ht areas of the scene. It is the deepness of the shadows that we need to obser= ve and evaluate in order to know whether the scene contrast will be relatively low, moderate or high, and that is one of the most important lighting effects that we need to understand.
Finally, it is important to recognize that “contrast” of a scene is not determined solely by the reflectan= ce of the objects in the scene – the quality of light illuminating the objects is equally important. In fact, the inherent contrast in a scene (a function of the reflectance of the elements in the scene) is constant and cannot be modified by the photographer. However, the resulting contrast in = the photographic image will be dramatically affected by the quality of the light (whether it is harsh and direct or soft and diffuse).
Later, we will develop guidelines for optimizing = our photographic interpretations based upon our analysis of the overall scene contrast.
What is Open Shade, and how does It Im= prove outdoor Portraits? Open shade is the shade created by a structure that bloc= ks the direct rays of the sun but at the same time allows the bright sky itsel= f to illuminate the subject.
The subject is near enough = to a large structure that he or she is completely in the shade of that structure= . At the same time, there is little or no blocking of the open sky above the subject. In other words, if the subject were under a canopy or roof that bl= ocks the sky, then that would be shade but not "Open Shade".
What are the Advantages<= /u> of Open Shade?
· The fact that there are no direct rays of the sun falling on the subject means that the scene will have lower contrast. T= he light that illuminates the subject will be from a large expanse of blue open sky and will be diffuse or soft, in comparison with the direct rays of the = sun. The effect on the image will be that the facial shadows will be lighter, so= fter and more detailed, and the highlights will be less harsh and more detailed.=
· Portraits made in Open Shade will have less contrast, softer shadows and more detailed highlights rather than having deep black shadows in the eye sockets and und= er the chin and nose.
· The subject will be able to pose without squinting.
· Blown out highlights in the background are a= voided.
· The camera's AutoExposure system is less likely to be confused by the extreme range of brightness3 in the scene and will more likely effect a correct exposure.
What ar= e the Disadvantages of Direct Sunlight?
· A subject illuminated by direct rays of the = sun will have very high overall contrast. In fact, the range of brightness on t= he subject will typically be greater than can be captured without special processing.
· The subject will usually find it difficult to keep his eyes open without severe squinting, and the shadows will be so deep and black as to be featureless ( without detail).
· The highlights on the subject will often be = such a bright white that they will be featureless (without detail).
· Mid-range tonal values will be very scarce &= #8211; most pixels will either be in highlights or in dark shadows.
What is the Quickest Way to Recognize an Overly Harsh or High Contrast Scene?
· Look to see if the subject is casting a deep black shadow on the ground. If so, the subject is in the direct rays of the= sun - not Open Shade.
For indoor scenes the lighting is assumed to be from incandescent or fluorescent lamps, sun, open sky and possible combinations = with reflectors or diffusers. We will discuss the similarities and differences w= ith respect to outdoor lighting.
When shooting indoors it is difficult to synthesize a = lighting situation that compares with Open Shade. The closest one could come to open shade would be to have a domed ceiling with indirect lighting such that the subject(s) are lighted with a diffuse light coming from the dome at all different angles. The next best thing would be banks of fluorescent tubes in the ceiling, or indirect lighting placed around the periphery of the room at near ceiling level. If such lighting is available, it should be taken advan= tage of. It is more likely, however, that the best thing available will be the daylight coming through a window with a northern exposure. The northern exposure guarantees no direct rays of the sun (in the northern hemisphere).=
Unfortunately, many indoor situations lead to shadows falling across the subject from two or three different directions giving ra= ndom combinations of shadows, and when the lighting you need just isn’t th= ere, the popular answer seems to be to use electronic flash, which inherently generates a high contrast scene because of being concentrated and direct.
Just as with outdoor shots, the real challenge is lear= ning what to look for in the results so that you know what has to be corrected. Again, harsh lighting works aga= inst you, and soft<= /i> lighting is generally better. It takes a great deal of intuition to look at= the results of a given lighting situation and figure out what must be done about it. Almost anything you can do to s= often the light or make it more diffuse will be an improvement.
Don’t make the assumption that all you have to d= o is shine a lot of light on someone’s face in order to take their photogr= aph. You would also like the resulting image to be as life-like as possible. That requires a delicate hand as you paint with light, using no more contrast th= an necessary.
Look at the shadows on the subject’s face. Is the pattern of shadows consistent with a single source of light or with multiple lights? If multiple sources are obvious in the shadows, then it is better t= o reduce the lighting down to one light that overwhelms any others. Then you can position that light to give the desired shadows – falling diagonally across the face so as to bring out the facial contours. With proper lighting the highlights and shadows work together to give the appearance of 3-dimensionality in a 2-dimensional image.
If the single light is too harsh it can be diffused by bouncing it off the ceiling or reflecting it from a reflecting parasol. Once you have the primary light providing the necessary modeling, you can apply = any necessary fill light from a secondary source to soften the shadows, as necessary.
Remember that high contrast is not desired in portrait= ure – there are dozens of different shades of shadow and dozens of differ= ent shades of highlights. The trick is to use no more contrast than is necessar= y to create the modeling of the facial contours in order to create the illusion = of reality.
A list of related articles has been provided in the End Notes. The article, “Portr= ait Lighting” is especially relevant.
1) "clinical" - V= ery objective and devoid of emotion; analytical.
2) "comprised" - = To consist of; be composed of.
3) Scene “Brightness” (digital) – In= the most common format (8-bit RGB), each color, Red, Green and Blue are present= at magnitudes of intensity from the lowest, (0), to the highest (255). For example, 127, 127, 127, represents the color middle gray in which the three colors are each present at the v= alue mid-way between the lowest intensity, (0), and brightest intensity (255). T= he scene brightness, or luminous intensity is the a= verage between the highest RGB channel and the lowest RGB channel.
4) “Contrast” – Absolute values of contrast are too complicated for our needs. All we need is the ability to recog= nize which of two scenes has the greater contrast. When the contrast of a scene is low= , the luminous intensity histogram is peaked more toward the center of the histogram ̵= 1; i.e., in the range 100 – 180 on the brightness scale of 0 – 255. Conversely, when the contrast is high, the luminous intensity histogram has= the energy divided more toward the deeper blacks and the brighter whites.
5) "Virtual image" - the image data as store= d in computer memory as the numerical values of individual elements of the image. The virtual image becomes an actual visible image when rendered on a graphi= cal device, such as a computer monitor or a print.
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