Characteristics of Light

INTENSITY

The ‘strength’ of the light. The same object under a more intense light will look brighter. The higher the wattage of a same type of bulb, the more intense the light it emits. In photography, light intensity is measured in ‘foot-candles.’

(Note that how bright things look depends only partly on the intensity of the light falling onto them. It also depends on how reflective they are. Black jeans look brighter in the sunshine than they do in the shade because the light falling onto them is more intense. A white shirt under the same light as the jeans will look brighter than the jeans because it reflects more light back.)

Fall-off
Imagine you are standing at the top of a very tall ladder, right up under a studio lamp aimed straight down the ladder. You take one step down the ladder; and the intensity of the light on the top of your head drops by half. Now imagine you are near the bottom of the ladder, under the same lamp. Take one step down the ladder…there is hardly any drop in the intensity of the light falling on your head at all.

‘Fall-off’ is about how rapidly or slowly a light drops in intensity. The closer an object is to a light source, the more rapidly the light drops in intensity, and ‘falls-off.’ The further away it is, the more gradually the light falls off.

Sunlight falls off very very gradually: a person can walk a mile up a mountain and you won’t notice any difference in the intensity of the light their face. Candlelight falls-off very rapidly: step a foot away from a candle, there will be a dramatic drop in the intensity of the light on your face. So.. to mimic sunlight, pick your most powereful lamp, and put your subject as far away as possible from it. To mimic candlelight, pick your least powerful lamp, and put your subject as close as you can to it. To mimic a desk lamp… a street lamp…

CONTRAST

Contrast is about the separation of tones in an image. The higher the contrast, the greater the separation of tones.

Motion picture photographers will often refer to the contrast between the intensity of the lit (key) side and the shadow (fill) side of the subject, expressed as ratio. A 2:1 ‘key to fill’ ratio means the light on the key side is twice as intense as it is on the fill side; in other words, there is one f-stop difference between them. This is considered relatively low contrast, or ‘flat’ lighting, typical of conventional studio portraiture, and broadcast television interviews. A 4:1 ‘key to fill’ ratio means the light on the key side is four times as intense as the light on the fill side; in other words there is a two f-stop difference between them. A ratio greater than 4:1 is starting to get into the kind of contrastiness that analogue film handles much better than video. An 8:1 ratio is considered very contrasty for video, only somewhat so for many film stocks.

Photographers are also often concerned with the overall range of brightnesses within a shot, and will talk about this in terms of of an f-stop difference between the brightest and darkest areas of the scene, taking into account not just light intensity but also the reflectivity of objects. The concern is usually whether the range of brightnesses within a scene will or will not fit within the range of brightnesses that the video or film stock can render in detail. Generally speaking, the greater the contrast between the brightest and darkest areas of a scene, the more likely it is that the video or film stock will not be able to render both the bright areas and the dark areas in detail.

SPECULARITY: HARD VS SOFT.

The easiest way to recognize a hard vs. a soft light is to look at the shadow lines. When hard light casts a shadow there is a sharp, hard-edge distinction between the light and its shadow. When soft light casts a shadow it’s hard to say for sure where the light stops and its shadow starts. The distinction is gentler, less ‘edgy’, more graduated. Hard light is generally more reflective than soft light: it will pick up the sheen of a leather jacket, or a sweaty forehead where softer light will not.

Hard light comes from specular—small, point-like—sources. The smaller the source, the more parallel its rays, and the clearer the distinction between light and shadow. Soft light comes from large, broad sources. The broader the source the less parallel its rays, and the fuzzier the distinction between the light and its shadow.

Size is relative. The sun, thought admittedly a gigantic source, is so very very far away that it is very very small in relation us, and so effectively a small, close to point, source. A 3-foot square ‘softlight’ backed-off to cover a car is small (and not all that soft), but lighting a watch, enormous (and very soft).

The sun, on a clear day, is a very small source, casting a very hard light. On an overcast day, the sun is diffused—spread out—over the whole breadth of the cloud cover. It it now a very large source, casting a very soft light. Similarly, a bare bulb casts a harder light than a bulb inside a rice-paper lampshade, or turned to bounce off the whole of the ceiling.

To soften a hard light, make the light source bigger, broader, in relation to the subject: diffuse it over a larger surface area—shine it through a sheer curtain, bounce it off a ceiling— and/or bring it closer to the subject.

COLOUR

If red, green, and blue light shine on the same spot, the spot will appear white. You can think of white light as made-up of these three colours—the additive primaries of light—aka RGB. Light will appear coloured if strongly deficient in one or more of the primaries.

The human eye, with some help from the brain, accepts a broad range of light sources as white that are, in fact, composed of unequal amounts of the primaries. Daylight is bluish; standard ‘indoor’ Tungsten bulbs emit an orangey light; most fluorescents emit a greenish light. If we take both daylight and tungsten light into the same view (imagine looking at a desk lamp in front of a window), we can sort of see the difference: the indoor light looks warm and cozy against the cooler light outside. But if we are looking at things under only one or the other (imagine walking around outside in daytime), our brain makes adjustments so that we see the light as pretty close to white.

The video camera is not so accommodating. It sees colour deficiencies as they really are, physically speaking. It does not adjust them to read as white—unless we tell it to.

When we ‘white balance’ a video camera, we are telling the camera what colour of light we want it to read as white. Usually we are telling the camera to read as white a light we ourselves already see as white: an ‘indoor’ tungsten light (which we see as white but is actually orange) or the ‘outdoor’ daylight (which we see as white but is actually blue).

Some situations involve more than one kind of light source, and so different colours of light. These are known as ‘mixed light’ or ‘mixed source’ conditions. The standard way to deal with mixed indoor/outdoor light is to put blue gels on your indoor Tungsten lamps, to make their orangey light the same colour as bluish daylight. You then white balance for the now consistently bluish light—i.e. tell the camera to see it, like we do, as white.

DIRECTION

When we talk about the direction of a light, we are talking about where the light is coming from, in relation to the subject, as seen from the position of the camera.

Light coming from directly behind the subject is called backlight. Subjects lit with a backlight alone are rendered in silhouette: we see no detail on the camera side of the subject; it is entirely in shadow. A backlight outlines the shape of things; helps distinguish the subject from its background.

Light coming from 3 ‘o’clock or 9’oclock is called sidelight. Side-lit subjects are half lit, half in shadow. Sidelight tends to accentuate the three-dimensionality of things, and to bring out the texture of surfaces (plaster, pock-marks, wrinkles, noses).

Light coming from directly in front of the subject is called… ‘front light.’ The camera-side of the subject is entirely in the light, and the shadow falls directly behind the subject, where we don’t see it. With no shadow to cue us to the three-dimensionality of things, we lose our sense of the shape of the subject; it looks ‘flat.’

Light coming from half way between side and front light is called ‘3/4 front light,’ or simply ‘3/4 front.’ A ¾ front light puts the subject mostly in light, but retains enough shadow area to give a sense of its shape. ¾ front is often the default position for a key-light, especially in portraiture.

Light coming from halfway between sidelight and backlight is called ‘3/4 back light,’ or simply a ‘3/4 back.’ A ¾ back placed on the opposite side of a side or 3/4 front light, adds a sliver of a highlight on the shadow side of the subject, at the same time as it helps to differentiate the subject from its background. A ¾ back light, coming from below, is sometimes called a ‘kicker.’
Low angle light (coming from below the subject) casts shadows upward, lending a ghoulish look to faces, especially if it is a (rarely seen in nature) hard low angle light. Soft low angle light is not nearly so instinctively disturbing.

High angle light (coming from above the subject) casts shadows downward. It can shade-in the eyes of people with deep eye sockets. A top light is a light that shines down from directly above the subject. Outdoor scenes lit by the noonday sun can seem more two-dimensional, ‘flat’, due to the lack of shadows when the sun is directly above us.