Lamps that work by burning filaments are the most traditional kind of artificial illumination, with a low color temperature but a continuous spectrum.
Specifically, the color temperature of a light source depends on the energy output (in watts), as we saw before, and is significantly orange in relation to daylight. Because incandescent lamps and the sun generate light by the same mechanism—burning—they are perfectly known quantities and are no problem for photography.
Non-incandescent lighting, however, is another matter, and is increasing in use. Most modern artificial lighting relies on the visible emissions from specific elements, which are always limited and never as pleasing as continuous-spectrum light. The development of lighting engineering has led to a growing variety of these non-incandescent lamps (another description often used is non-black-body lighting). All of them, from fluorescent to vapor-discharge lights, make use of specific chemical elements that are in one way or another excited to emit light. However, while incandescent light—from the sun to a flame—emits a continuous spectrum of wavelengths, individual chemical elements emit just a very narrow part of the spectrum. The emission spectra for these lamps have the appearance of a group of isolated narrow spikes. No single element on its own gives anything like the full spectrum of daylight, but by carefully choosing a group of elements it is possible to get close to its appearance to the human eye. This is mimicking a continuous light source, and how well it does this depends on the engineering design.
What matters to photographers is artificial light that is close to the quality of either sunlight or incandescent lamps, but this is only one of the aims of lighting designers. Other things may have a higher priority, such as efficiency, brightness, and cost. Ultimately, judgments about lighting are largely subjective, but in the lighting industry there are attempts to quantify it. One key concept is chromaticity, which is a measure of the quality of light as defined by its purity and dominant wavelength. Purity is akin to saturation and the wavelength is equivalent to hue. Both the CCT (Correlated Color Temperature) and the CIE x and y coordinates define this.
TUNGSTEN HALOGEN
Downlighters used here in a modern Japanese tea-ceremony room are low-voltage (12v) tungsten halogen lamps. These burn brighter and hotter than standard incandescent lamps, and so at a slightly higher color temperature, and the low-voltage variety can be made smaller.
The problem for interior photography, as shown in the main images here, becomes entirely understandable when the spectral power distribution is compared between tungsten (left) and fluorescent (at 5000 K, right). Not only is the red deficient, but more important, there are green spikes from the mercury.
2800 K INCANDESCENT HOUSE LAMP
5000 K FLUORESCENT
Notice the mercury energy spikes
DISPLAY WINDOW
Incandescent lamps behind a diffused screen at a restaurant. The diffusion spreads the fall-off in illumination around each lamp, and the apparent color. Overexposure near the center of each lamp records as close to white, shading to yellow and orange as it becomes darker.
But because lighting that does not have a continuous spectrum is unlikely to be perfect in the way it renders all colors of all objects, another scale is needed, one that rates the lighting based on visual experience. The Color Rendering Index (CRI) is used by manufacturers to give an idea of how closely their products come to continuous lighting as perceived by viewers. It is based on a viewing test of eight pastel color swatches, which admittedly is not very many, and is one measure of metamerism (see here). Both daylight and artificial incandescent light rate 100 on a scale from 0 to 100. The very best fluorescent lamps reach about 90, but poorer, cheaper ones can rate as low as 50, while some vapor-discharge lamps, such as sodium, can be much lower still. Another view of the CRI is that it is a measure of how “pleasing” a light source is, and indeed this ultimately is what is important in most photography. All the settings and post-production work that goes into correcting images shot under fluorescent and vapor-discharge lighting is essentially concerned with making the results believable and pleasing. Fluorescent and the various flavors of vapor-discharge lamps differ considerably in the way they work, but for photography they present essentially the same (and considerable) problems.
FLUORESCENT IN CONTEXT
A compromise white balance for an evening shot that includes fluorescent lighting on the ground floor of this modern Japanese house, tungsten on the floors above, and a clear sky behind, reveals the essential greenness of typical fluorescent lighting.
Light source
CRI
Sunlight
100
100 W incandescent lamp
100
Metal halide 5400 K
93
Deluxe pro warm white (Philips)
92
Deluxe cool white fluorescent
86
Metal halide 4200 K
83
Daylight fluorescent
76
Deluxe warm white fluorescent
73
Cool white fluorescent
65
Warm white fluorescent
55
White deluxe mercury
45
High pressure sodium
25
Clear mercury
17
Cow pressure sodium
0-18
Source: Illuminating Engineering Society. Interim Method of Measuring and Specifying Color Rendering of Light Sources, LM-19, NY, 1962.
Fluorescent lighting is spreading, particularly into homes and other spaces that were traditionally lit with tungsten. Concerns about energy conservation are encouraging this kind of conversion, and while photographically fluorescents are less predictable than incandescents, this is an inevitable process of change. Clearly, the ability to set the white balance in a digital camera makes all this manageable in a way that it was not with traditional film, but there are still issues.
Fluorescent lamps work by passing an electric current through a gas-filled glass envelope, typically a long circular tube (hence the popular name strip-lighting). The gas produces ultraviolet light that strikes the coating on the inside of the tube, which is a coating composed of a mixture of fluorescent compounds. These fluoresce (glow), for as long as they are bombarded with the ultraviolet light. The newest types have coiled tubes to make them suitable for replacing standard tungsten fixtures, and are known as CFL (Compact Fluorescent Lamps).
SUBWAY
A new Tokyo subway station uses fluorescent lighting as part of the design. With the view consisting of concrete walls and ceiling, Auto white balance is an easy and satisfactory solution.
Because each of the fluorescents emits light in a very narrow band of the visible spectrum, the skill in designing these lamps lies in blending a range of them so as to approximate the full continuous spectrum that we are accustomed to from white or incandescent light. The key word, nevertheless, is “approximate,” because there are always spikes, or gaps, or both in the emission spectra of fluorescent lamps. The human eye accommodates well to this slightly broken spectrum, and of course most of them are designed for human vision. The camera sensor, however, reveals any imperfections all too clearly. Fluorescent lamp design varies widely, not only on the scale of cool to warm (lamps tend to be classified as cool-white, warm-white and so on), but in the color casts they give that are not visible to the eye at the time. Even the high CRI scores given by manufacturers do not tell the entire story. The spectral energy distribution is not coherent and there will always be some discrepancies in yellow and green, as well as poor coverage in red and blue.
OUTDOOR VAPOR DISCHARGE
The foreground lighting in this night-time view of the Golden Temple, Amritsar, is vapor discharge. This strongly blue-green light, contrasts with the orange of the incandescent-lit Golden Temple itself, behind. In this instance, the color contrast helps the image.
ARTIST’S STUDIO
A Beijing artist’s studio lit by multi-vapor lamps high in the ceiling. In this kind of situation, in which there is no other lighting for comparison, and in which the colors of the paintings need to be accurate (that is, grays neutral), aiming for a neutral white balance is the best option.
FLUORESCENT LIGHTING
This underground railway station platform is lit with Fluorescent lighting. In the far distance, it is apparent a different kind of lighting is used in the stairway.
The important thing to remember is that in most photographs it is the appearance that counts. Occasionally, you may have a need for absolute accuracy, and there are ways of doing this (see here), but most of the time the color simply needs to look acceptable to someone viewing the finished image.
The white balance camera settings are the first point of control, essential if you are shooting JPEG or TIFF, less so if you are shooting Raw. The difference is that with the first two formats, the camera will process the image and deliver a particular color balance as you shoot. With Raw, the white balance settings are kept separately from the Raw capture data, allowing you to choose which color temperature and hue/tint you prefer during post-production.
Clearly, as long as you don’t mind spending extra time on the computer, Raw has the advantage. Nevertheless, even though any white balance can be chosen at this later stage, there are some advantages to choosing the best-looking white balance at the time of shooting. One is that it gives you an opportunity to check the result at the time by comparing the LCD screen with the scene. Admittedly, the camera screen does not give an ideally calibrated view, but it is better than nothing. The fluorescent settings (there may be more than one according to the model of camera) are the obvious choice, but as fluorescent color casts are unpredictable, they are not necessarily the best. Also consider using the auto setting, and varying the color adjustment if your camera has this. With more time available, set a custom white balance, although this can be a complicated procedure.
MIXED LIGHTING: WELDING
The temperature at the tip of a welding arc typically exceeds 6500 K, giving a bluish light when seen against the background of filtered daylight in this studio.
In any case, you must judge the way the color of the scene looks to you in some way, and this is especially important for Raw shooting. It often helps to remember a key color, and if there is a gray or other shade of neutral in the scene, this is worth noting. If you have time, one great help is to place a color target such as a ColorChecker in the scene and take a reference shot. Unless you need total accuracy, you do not need to perform a thorough profiling—simply being able to compare the target visually with the image is likely to be sufficient. You can also perform a basic balance by using the Gray Point dropper in Curves or Levels.
The problem of the sometimes strange cast from a broken spectrum can go beyond just the sensor’s reaction. The eye also can receive different color information from that seen under daylight. Metamerism is when two color surfaces appear the same under one light (such as daylight) but different from each other under another light (as often happens with fluorescent lighting). This doubles the difficulty of judging how a scene should appear, and there is no obvious solution. Just be aware that some colors may shift independently of the majority.
Now more widely used, vapor-discharge lamps are capable of high output and come in several flavors, the color depending largely on the type of gas. They share their basic principle with fluorescent lamps passing an electrical discharge through a gas. Here the gas contains metal vapor, which emits light, and Mercury is one of the principal components. The problem for photography is in the broken spectrum and emission spikes, and also in the shortage of long red wavelengths. The eye is less sensitive to the missing long red wavelengths than both film and sensors, and tends to accommodate the color output, seeing it as more or less white, while the sensor records it as more blue/green. In addition, red surfaces in a scene will tend to look darker and duller, again because of the deficiency in longer red wavelengths.
MIXED LIGHTING: DAYLIGHT AND INCANDESCENT
Daylight reflected from a courtyard, entering the scene from the right, contrasts with the incandescent lighting entering from the left. Their effect is very noticeable on the white clothing of this priest in a Shanghai temple. As in many other situations, two opposed lighting sources in one image has the potential to be attractive rather than a problem.
MIXED LIGHTING: MARKET
A street market in Kuala Lumpur contains a mix of daylight with 2800 K incandescent lamps hanging over each stall.
A few subjects reveal themselves in an image only by means of motion blur. One of the most obvious is a firework display. Even to the human eye, it is the rapid movement of points of light appearing as streaks that create the intended effect. A sharply frozen image taken at a short shutter speed would look like nothing more than bright points. Unless there is a significant amount of drifting smoke illuminated by the explosions, the shutter speed will have no significant effect on the overall brightness of the scene; instead, it determines the length of the streak in the frame. Generally, the longer the better, although it is usually sensible to keep one exposure to one burst of the display. The wider the angle of lens, the more certain you are of framing the display fully, but in any case, pay attention to the first burst for predicting the position of subsequent bursts in the sky. An alternative technique with a telephoto lens is to loosen the tripod head slightly, follow the rocket trail upwards, and when it reaches its highest point, quickly lock the head and open the shutter.
One fairly obvious method of handling a scene lit by different types of light source with opposing color balances is to treat it as two (or more) layers, one for each light source.
The principle is to concentrate first on color correction for each light-source layer at a time, and save the problem of combining them until later. Thus, for one image layer, you should focus entirely on only one light source, ignoring the effects this has on parts lit by any other source. For the next layer, do the same for the other light source. With three or more different light sources this can become unnecessarily complicated, but with two it is perfectly manageable.
The color adjustment method can be any of the ones discussed previously, including setting the Gray Point or White Point, applying a complementary overall color filter (Photo Filter in Photoshop), Hue/Saturation sliders, Color Balance sliders, and others. This depends very much on being able to identify which parts of the scene have been lit—and therefore color-shifted—by which light source, and this will be easier in some photographs than in others.
The next step is to blend the two (or more) layers in a sensible and realistic way. Again, Photoshop offers a huge variety of ways of doing this, but it is probably wise not to get obsessed with the relative merits of each method. In the end, we are dealing pragmatically with photographs. If the influence of each light source is clearly related to an obvious value, such as brightness, there is likely to be a procedure that can blend the layers simply. In the example here of the Japanese table detail, the brightness of the recessed glass lamp meant that incandescent lighting, at around 3000 K, affected most of the highlights in the scene, while the shadow areas were for the most part lit by the much bluer evening daylight (around 6000 K). This made a procedural blend an easy choice, using some trial and error with the Blending Options from the Layers palette, and settling on Soft Light.
A glass artwork set in a table and lit from beneath. Photographing it at dusk gives a choice of two very different color temperatures. Fortunately, most of the incandescent lighting is at the high end of the tonal range, giving the opportunity to blend the two images as layers, selecting the blend on the basis of brightness (orangier version underneath).
INCANDESCENT WHITE BALANCE
DAYLIGHT WHITE BALANCE
THE FINAL RESULT
Blending options, deselecting the darker tones from the upper layer.
A different approach to the same problem. Daylight entering from the small window contrasts sharply and not very pleasantly with the incandescent lighting of this bathroom.
Incandescent white balance
Daylight white balance
The bluer (incandescent) version is pasted in as the upper layer. The unwanted, overly blue areas are erased with repeated brush strokes.
The result lacks some punch, so a low amount/ high-radius USM filter is applied to the flattened layers.
Otherwise, a hands-on approach using erasing or brushing, allows more personal choices. One obvious choice is to erase the “wrongly lit” areas from the upper layer, paying careful attention to the size, opacity percentage, and hardness of the brush. Another is to use the History Brush. In this case, one method is to make the necessary color adjustments to one image, add another layer with its own, different adjustments, flatten the image, and use the History Brush tool to restore selectively from the original. This is more complicated to set up, but some people find restoring more intuitive than erasing. If you are using brushes in any of these ways, make sure that the number of History States is set high enough in Preferences before you start.
A direct approach to the problem of mixed light sources is to select the color effect of one and then shift it or filter it toward a more pleasing or neutral result.
There are a number of ways of targeting specific colors in an image, and these vary according to the image-editing software, and whether you’re working on a Raw file, converted JPEG, or TIFF. If you’re working on converted files, beginning with Photoshop, the two most convenient are Replace Color (see here) and Hue/Saturation, both found under Image > Adjustments. Hue/Saturation has been around for a long time, and Replace Color is actually a more focused version of the procedure, with an added preview of the areas selected. In either case, the technique involves first selecting the most intense area of the offending color, and adjusting the range of the selection. The three parameter sliders Hue, Saturation, and Lightness can then be adjusted to taste. In Hue/Saturation, once you have selected a color range from the drop-down menu, clicking on part of the image will refine that selection. A third procedure that is less intuitive is Selective Color, also under Image > Adjustments.
There are two possible drawbacks to these otherwise excellent and easy techniques. One is that the choice of color alteration is not fully flexible. It relies on Hue shift by degree, Saturation, and Lightness, and misses out on arbitrary color filtering (such as Photo Filter, also under Image > Adjustments) and contrast control. The other drawback is when a targeted color also covers other objects and surfaces in an image that you do not want to change. In the latter case, for example, imagine a blue vase in an interior view lit by both incandescent light and daylight. If you decide to select the blue cast from daylight and shift that, the same effect will happen to the vase. A sensible and manageable solution is to use the History brush to restore those areas.
A more laborious, but potentially more accurate, method of selection is to define the areas of the image that you want to change. There are several ways of doing this, including such selection tools as the Magic Wand, Quick Selection tool, or Color Range feature to name a few. These create selections that can then be modified by expanding, contracting, selecting similar values, and so on. Alternatively, there is direct mask painting, which can then be used as a selection. Often, selection is more accurate by using a combination of these methods; for instance a quick selection by first using the Magic Wand, converting this into a mask, then modifying by erasing and painting, and possibly blurring.
Increasingly Raw conversion software, such as Apple Aperture and Adobe Lightroom, allows for basic selections to be made. This makes it possible to amend localized regions of an image, such as a selective color change. Another example of Raw conversion software, DxO Optics Pro, features a Multi-Point Color Balance tool that negates the need for selection by allowing the user to shift several points while viewing a preview on the right of the screen (see here). All these Raw converters make non-destructive editing much more easily accessible to photographers who have become used to the many tools in “pixel” image editors (such as Adobe Photoshop) which act on specific areas of an image. And because you’re working on unprocessed 12- or 14-bit Raw data, the results will have fewer artifacts.
Color balancing in DxO Optics Pro, called Multi-Point Color balance, allows several points to be clicked, and then the color shift specified by dragging around a color wheel.
The image as opened in DxO, original on the left, changes applied on the right. This is the default, with some automatic corrections.
The first point is in the shaft of light, which I want to be neutral. Note that sampling very bright tones can create huge shifts in the rest of the range, but this will be taken care of in the next sample.
The second sample is in the water, which I want to make more vivid. The third and final sample is on the stalactites at right, which are too red because of the incandescent lighting.
In Lightroom we can make a selection and apply a localized color change.
Compared with the daylight illuminating the near ceiling tiles, the farthest part of the room appears too “hot.”
Using Lightroom’s Adjustment Brush and its associated sliders, a selection is quickly made of the offending area. Here we’ve selected Color mode.
Selecting a light blue to “paint” over the reddish cast provides a more balanced result.
Photoshop’s Replace Color tool replaces areas of color without selecting them separately.
Original
The exact sample points are critical. Red dots mark the points sampled, and show the importance of finding the point that encompasses the entire area that we want to shift.
With the precise sampling point finalized, the hue is lowered slightly, as is the saturation, and the lightness increased, all to match the rest of the steps.
The result judged a little too yellow.
The final result
Using Selective Color, the yellows are chosen, and their precise hue manipulated for a more neutral, creamier effect.