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DiffusedlightCeiling

A good example to illustrate the difference between hard and soft shadows: Through a very narrow opening of curtains, daylight is falling into this hotel room. Horizontally, the opening is only a few centimeters wide – the corresponding shadows are very hard. The vertical shadows, however, are very soft because the curtains let some light in from the ceiling to the floor. In the studio, this effect can be simulated with a Striplite 60, a litestick and with narrow softboxes like the 30x120 or the 30x180 cm softbox, especially when these are equipped with the additional strip mask.

Diffused lighting fixtures

Polarization of light is very useful in many aspects of optical microscopy. The microscope configuration uses crossed polarizers where the first polarizer (termed: the polarizer) is placed below the sample in the light path and the second polarizer (termed: the analyzer) is placed above the sample, between the objective and the eyepieces. With no sample on the microscope stage, the light polarized by the polarizer is blocked by the analyzer and no light is visible. When samples that are birefringent are viewed on the stage between crossed polarizers, the microscopist can visualize aspects of the samples through light rotated by the sample and then able to pass through the analyzer. The details of polarized light microscopy are thoroughly discussed in our microscopy section of this primer.

Unpolarized incident light (natural sunlight, for example) is polarized to a certain degree when it is reflected from an insulating surface like water or a highway. In this case, light waves that have the electric field vectors parallel to the surface are reflected to a greater degree than those with different orientations. The optical properties of the insulating surface determine the exact amount of reflected light that is polarized. Mirrors are not good polarizers, although many transparent materials will be very good polarizers, but only if the incident light angle is within certain limits. In this case, the particular angle inducing maximum polarization is known as the Brewster angle given by the expression:

Diffused lighting interior design

Average soft light sources have about the same sizes as the objects or set-ups they illuminate: Let’s say a 50 by 50 cm softbox for a narrow-cropped portrait or an 80 by 140cm softbox for a full-body shot. The shadows on the under- and backgrounds are still clearly visible, even when they are not sharply defined anymore. Big parts of these shadows show gradations, and a small core shadows still exist. Small and fine details, however, do not appear in the shadow. The texture of our object is now shown in lower contrast and is therefore not as clear as in hard light. Soft light still increases the contrast of the object a little, but less than a hard one. The color saturation finally is somewhere in between the one derived from a hard light (high) and a diffused light (low). Being soft, our light source got a certain size (it is not a point anymore) and the distance from it becomes very important: The closer we get, the bigger the light source becomes (seen from the perspective of the object or model). This means that our light becomes softer when we get closer, and harder, when we use it over larger distances. A light of about 100 by 100cm placed at 4 meters from the model has the same hardness as a source of half the size (50 by 50 cm) at half the distance (2 meters). Due to the inverse square law, we expect other effects (higher contrast when placing the light closer to the object or model). When we bring the 100 by 100 cm softbox to half the distance (we will have to reduce the power by about 2 f-stops) the light will be a lot softer.The following light shapers can be used as soft lights:

The light does not show any direction anymore and the only contrast remaining in the photograph is the contrast of the object itself. The structure of the object’s surface is as flat as possible, almost invisible and the color saturation is heavily reduced.The following light shapers can be used as diffused lights:

DiffusedLightBulb

Now the light source is huge. Shadows no longer exist as the light is big enough to shine all around the object or model.

The lenses of the sunglasses have polarizing filters that are oriented vertically with respect to the frames. In the Figure 2 above, the blue light waves have their electric field vectors oriented in the same direction as the polarizing lenses and, thus, are passed through. In contrast, the red light wave is perpendicular to the filters and is blocked by the lenses. Polarizing sunglasses are very useful when driving in the sun or at the beach where sunlight is reflected from the surface of the road or water leading to glare that can be almost blinding.

When current is applied to the electrodes, the liquid crystalline phase aligns with the current and loses the cholesteric spiral pattern. Light passing through a charged electrode is not twisted and is blocked by polarizer 2. By coordinating the voltage on the seven positive and negative electrodes, the display is capable of rendering the numbers 0 through 9. In this example the upper right and lower left electrodes are charged and block light passing through them, allowing formation of the number "2".

Natural sunlight and almost every other form of artificial illumination transmits light waves whose electric field vectors vibrate in all perpendicular planes with respect to the direction of propagation. When the electric field vectors are restricted to a single plane by filtration, then the light is said to be polarized with respect to the direction of propagation and all waves vibrate in the same plane.

This concept is illustrated in Figure 1 below, and we have also constructed an Interactive Java Tutorial that explores the interaction of light waves with polarizers. In this example, the incident light electric field vectors are vibrating perpendicular to the direction of propagation in an equal distribution of all planes before encountering the first polarizer. The polarizers illustrated above are actually filters containing long-chain polymer molecules that are oriented in a single direction. Only the incident light that is vibrating in the same plane as the oriented polymer molecules is absorbed, while light vibrating at right angles to the plane is passed through the first polarizing filter. In Figure 1, polarizer 1 is oriented vertically to the incident beam so it will pass only the waves that are vertical in the incident beam. The wave passing through polarizer 1 is subsequently blocked by polarizer 2 because the second polarizer is oriented horizontally with respect to the electric field vector in the light wave. The concept of using two polarizers oriented at right angles with respect to each other is commonly termed crossed polarization and is fundamental to the practice of polarized light microscopy.

Diffusedlightfor Photography

This type of polarized light is often termed glare and can be easily demonstrated by viewing the distant part of a highway on a sunny day. The reflection and polarization of light according to the Brewster theory can be more thoroughly examined with our Brewster’s Angle Java Tutorial. Light reflected by the flat surface of a highway is partially polarized with the electric field vectors vibrating in a direction that is parallel to the ground. This light can be blocked by polarizing filters oriented in a vertical direction as illustrated below in Figure 2 with a pair of polarized sunglasses.

Diffused lighting examples

What are the three basic categories of light? Looking at the hardness (or softness) of light is certainly the most simple and easy way to classify it. However, we can never call a certain light shaper hard or soft (with the exception of a point light source that is always hard). Depending on the size and the distance between the object and the light, the same light shaper can once be hard, soft or even diffused. Let’s have a closer look at these three categories:

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One of the most common uses of polarization today is the liquid crystal display (LCD) used in numerous applications including wrist watches, computer screens, timers, clocks, and many others. These devices are based upon the interaction of rod-like liquid crystalline molecules with an electric field and polarized light waves. The liquid crystalline phase exists in a ground state that is termed cholesteric where the molecules are oriented in layers where each successive layer is slightly twisted to form a spiral pattern. When polarized light waves interact with the liquid crystalline phase the wave is "twisted" by an angle of approximately 90 degrees with respect to the incident wave. This angle is a function of the helical pitch of the cholesteric liquid crystalline phase, which is dependent upon the chemical composition of the molecules (it can be fine-tuned by small changes to the molecules).

An excellent example of the basic application of liquid crystals to display devices can be found in the seven-segment LCD numerical display (Figure 3). Here, the liquid crystalline phase is sandwiched between two glass plates that have electrodes attached similar to those depicted in the illustration below. In figure 3, the glass plates are drawn with seven black electrodes that can be individually charged (these electrodes are transparent to light in real devices). Light passing through polarizer 1 is polarized in the vertical direction and, when no current is applied to the electrodes, the liquid crystalline phase induces a 90 degree "twist" of the light and it can pass through polarizer 2, which is polarized horizontally and is perpendicular to polarizer 1. This light can then form one of the seven segments on the display.

Looking at the light of a point light source, we will see very clearly defined shadows. On a background or underground there is either light or shadow, but nothing in between, no gradations. Even the finest details provoke a clear shadow. The structure of any object (e.g., textile, skin) is pointed out very clearly. A very hard light source is the only one that does not change its characteristics if we vary the distance to the object (but according to the inverse square law it does change the power). The shadows remain the same: very sharp. Hard lights may increase the contrast of the object. The areas directly lit may be burnt while the shadows remain very dark.The hardness of the light finally has an influence on the color saturation. Small and hard lights increase the saturation of the picture while soft, and especially diffused lights reduce it.