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Physics/Science of Light (PART 4)

Physics/Science of Light
(How you could implement it + create dramatic compelling art scenes)

Light: Exposure

Exposure affects value. Eyes and cameras have to adjust for the amount of light in view. If one area of light is over and under the adjustment threshold, that information flattens out and loses colour.

If we map out a scene using a histogram on a camera, the top of the vertical axis will indicate the highest amount of light (photons) meanwhile the bottom of graph will indicate the least amount of photons. With both our eyes and the cameras we can see only a portion of the spectrum/range. Our eyes have a wider range than the camera but we still have a harder time catching everything that we see. This is because of the trillions and trillions of photons that are streaming and bouncing off of objects and then flying into our eyes from a bright light like the sun. It is difficult for our optic nerves, brains and senses to interpret all the information that bombards us. Even with the light source out of view, cameras have a hard time with bright light.

Essentially what happens in a camera on the histogram is, anything above the threshold (overexposed by light),anything outside of that range is going to flatten out in white.

And anything outside of the bottom range on the histogram is going to flatten out as black. Our eyes operate similarly, but what's different with our eyes is that our eyes are navigating while our brains are compensating for it. Our brains are making these calculations, like a complex computer would; constantly adjusting the exposure level in specific areas. Our irises are dilating and contracting to compensate for the amount of light that's coming in. Our brains can put together a picture that is more complete than a single camera image would be.

When the light source and shadows have the same exposure,(as shown above) the image tends to look very unnatural, it's become popular, we often see this type of range in HDR imaging. That's high dynamic range, so when people talk about HDR (High Dynamic Range) Imaging. Those who use this method try to take data that belongs to a larger part of the spectrum and compress it with the lower dynamic range. This is a process that a camera cannot do on its own. Often what they will do is brighten up the shadows(unexposed areas) and darken the sky in a landscape setting photograph; this application tends to make the image look unnatural.

According to this example (the red sphere) the top part of the sphere is being exposed to massive amounts of photons which are hitting our eyes or the camera sensor, our eyes/camera sensor can't handle that data so it blows out towards white.

Whereas in the middle of the sphere, there exists fewer photons but that area is still lit which allows to approximate what the actual local colour of the sphere can be. If we examine the shadow portion of the sphere, we can see that the information is lost and we're only left with darkness.

So if you were to paint a sphere with a regular lighting scheme it often helps to add just a bit of exposure on the top part; this enhances it with realism.

When exposed from the sky, the shadows become dark (underexposed).

It's a common occurrence when a strong main light source(ie. the sun) blows out (overexposes) portions of surfaces facing towards it. These overexposed areas doesn't always have to trend towards white but they can appear very de-saturated/dull as opposed to the areas that are underexposed (shadows) which usually appear more saturated. Notice how value, saturation, and hue are changed by exposure.

Nature usually has fairly simple lighting schemes.

Occlusion tends to lean towards more warm colours. There are exceptions to this but in a lot of cases it just looks right when you paint it in deep warmer colour, rather than a deep cooler colour or just a black or grey.


At dawn, things tend to be a lot bluer, because we have the blue lights in the sky(especially just before dawn) along with not having the direct sunlight present anymore.

The occurrence that's interesting about dawn, dusk or anytime of the time where the sun is at one side or the other is that we get a gradient in the sky. The gradient in the sky becomes a specialized area light source. During this time of the day we also have the sun as the light source; it has a slightly yellow/orange cast to it (especially in the morning).

Artificial Lighting:

Movies usually fake night lighting using filters and carefully controlled lighting.

Shade: Has soft blue cast, spots of sunlight are blown out.

Examining these leaves you're able to see how they're being lit from underneath (underneath them) from the ground and on the topside they're being lit from the sky; which causes them to trend more towards a blue tint.

Overcast: Light is very soft and neutral.

Bright Overcast
Bright Overcast:

Has sun diffused through clouds so there is a stronger directional light source.

With bright overcast, the sun is peaking through the clouds which causes it to diffuse within the clouds on one part of the sky. In this case, the sun is still behind the clouds and in this lighting scheme all of the shadows in the scene will become a lot softer. The forms become rounder, but you still get a definite direction of the shadows being cast.

Winter Lighting
Seasons affect the direction and colour of the light throughout the day.

During winter seasons, you tend to lose a lot of saturation because the skys during this time of the year tend to be hazy and overcast. The sun gets very bright and tends to blows everything out.

Light: Indoors

Indoor light is defined mostly by radiosity and occlusion. Window light will be coloured by what's outside (and will usually overpower other lights. You need to learn and practice more on occlusion and bounce light if you're going to painting indoor scenes.

Indoors +Sun Lit Bands of Lights

Dark rooms with a focused band of light coming from the sun can become the new light sources for indoors and start creating bounce light on the walls.

When you've got an enclosed room all of the surfaces in that room become light sources for your scene. Windows tend to be cooler than your indoor average lights. Indoor lights are usually going to be a tungsten bulbs which tend to be warmer. With that being said, when you have warm indoor light mixed with the cool light from the window, the two contrast interestingly with each other and you get a warm cool relationship going on.

When you're creating a lighting scheme it's always good to think in terms of warms and cools so you can set off two light sources from each other.

Of course when your indoors in a dark setting (as shown above), any specific areas that are being lit (such as sunlight coming in from the window) becomes the light source for the room.

Tungsten bulbs give off orange-coloured light. Almost any standard light bulb is going to give an orange cast light.

Many fluorescent lights have a greenish-blue cast.

Mixed lighting creates interesting colour combinations. When your mixing cool light sources with warm light sources or man-made sources with natural sources you tend to get some interesting combinations.

Candle or fire light is red-orange.


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