THE LAWS OF LIGHT

These are 3 laws and 1 effect that define how light travels. Because electromagnetic radiation is weightless and massless, Newton’s 1st and 3rd laws of motion are apparent in light's interaction with objects.

NEWTON’S LAWS OF MOTION:

1. An object in motion stays in motion unless acted upon.

3. For every action there is an equal and opposite reaction.

Because light has no weight or mass to physically move matter, the reactive force applies only to itself through every interaction. This is what makes it so easy to predict.

The following laws define how light travels:

Inverse Square Law
Law of Reflection
Law of Refraction
Diffraction (effect)

To be technical, this is 1 law of origin, 2 laws of travel, and the 4th is not a law, but affects travel due to the wave-nature of light.

It is not neat. Light as no obligation to fit into the box of human organization.

1. INVERSE SQUARE LAW

The inverse square law begins at light's inception point, when the photon is first created. This simply describes radiation intensity from an origin spread over distance. It applies to gravity, water, particle dispersion (like spray paint). This law takes effect every time light is expelled from matter.

We know that light travels forever until an interaction. The inverse square law says that light will shoot in all directions from a point source, and travel forever in all directions.

The result is that with a resource dispersed over distance, the intensity falls off at a calculable rate. And so a formula is derived from it: Intensity =1/d2

Where 1 is your initial intensity measurement. And d is the distance. Because your first measurement distance is arbitrary, it always equals 1, and further calculations are multiples of that original length. So for simplicity, its best to take a measurement in whole distances such as feet or meters.

This formula can be visualized in a few ways. A numerical value (such as f-stop), over a 2 dimensional curve graph, or volumetrically. But the formula presents that when you double the measuring distance, the intensity drops 2 stops (or becomes 1/4 of the last intensity). So, numerically, a first measure at f11, when double that distance, your meter will read f5.6. Double the distance from your previous measure, now f2.8. Double previous measure again, now f1.4 and so on. The result is a quick decline and slow taper off.

To calculate it visually, a known intensity must first be established, then double that distance from the source will be 25% of the previous measured intensity. You may calculate again at twice the distance from the second measurement, the intensity will be again 25% from the second measurement.

2. LAW OF REFLECTION

The law of reflection states that a ray will reflect off a surface at opposite the angle of impact. We use the normal, a 90 degree dividing line of the surface, to identify the impact angle to be mirrored on the reflecting side. Reflection is functionally the same as Newton's first law, for every action there is an equal and opposite reaction. And since light is massless, it can't push anything away, therefore it acts wholly on itself.

The law of reflection is easily visualized on a graph. A laser on a mirror is the same effect.

So the chain of custody of light so far would be: Light will shoot in all directions, and travel in a straight line forever until it hits a surface and reflects at opposite the angle.

The law is simple and surface randomness of materials are the reason for diffuse scattering. This is why uniformly flat surfaces reflect the most in the opposite impact angle.

When a surface is not uniformly flat (like a mirror) but is uniformly random, like a sanded surface or fine powder, then the reflections do not collectively exit in the same direction, but random directions, this is a matte surface. Most materials you see in the world are a mix of matte and smooth surfaces. Sometimes they are layered on each other, such as the smooth reflective layer of oil on human's matte skin. Although the older you get, the more stretched and reflective your skin gets.

3. LAW OF REFRACTION

This is otherwise known as Snell's Law. A mechanic not witnessed by eyes commonly, refraction describes light as it passes from one medium into another. For example from air to glass. Or from glass to water. In this case the impact angle refracts, aka bends (slows), into the second medium, determined by the new material’s density. If it exits back into the original medium, it will continue in the original angle of impact.

This is because every material that light may pass through carries with it a different density that slows light travel. This is called the refractive index, a number denoting the material's density. When impacting at an angle, light changes directions as it travels in the slower medium (what we call "bending").

If you were to string a variety of differing mediums together and shoot light into it at an angle, you would see the ray bend in slightly different directions as it crosses the next threshold. This is the basis for optics design. Together with altered glass densities, new optics designs can be made smaller and sharper.

On a film set, on the fly judgment of refraction is incalculable. Most surfaces that refract in our world are glass and water, neither of which are squared or straight to a camera lens typically. But this helps you understand the effects you might see when you encounter clear irregular surfaces.

4. DIFFRACTION (EFFECT)

Diffraction describes the apparent bending of a wave around corners. A perfect two-dimensional analogue is water. The more similar in size and sharpness the edge is to the wave, the more prominent the effect is. Waves react most intensely to edges similar to or smaller than its wavelength. As the edge increases in size, the effect decreases in intensity because the transition from edge to void is more gradual. As a result radio waves that are the size of mountains, will diffract around mountains, but visible light being smaller than the mountain doesn't. Visible light will diffract around it's 300-700nm wavelengths.

There is no formula for this. It is relative to the wavelength size. It is visualized by the image to the right.

At first glance, it may seem that diffraction would be its own scientific law. But the mechanic by which diffraction occurs is more complicated than it appears to our eyes. That’s why I described it as the apparent bending around corners. To our Newtonian brains, the wave seems to wrap around objects. To understand what is informing this reaction, we must look back into the nature of how light originates.

A great mathematical explanation treats the wavefront as infinite points of spheres of energy that emits in all directions in accordance with the inverse square law. However, The neighboring atoms also produce a sphere of energy, and collectively all the spheres cancel each other out except for the one spot that is open for energy to escape, which is in one direction. This shoulder-to-shoulder chain of canceled wavelets results in a wavefront. When these wavefronts reach an opening or an edge, there is a natural void. In this void there is nothing to cancel out this spherical wave that has just passed it, and so the spherical waves push out in accordance with the inverse square law as it would have naturally if there wasn't a cancellation wave next to it. It’s called the Huygens-Fresnel principle.

The Huygens-Fresnel principle is a phenomenally accurate classical approximation that models how light appears to behave under wave optics. However the "spherical wavelets" don’t physically exist, they are mathematical constructs that yield the right result.

The true explanation is Quantum Electro Dynamics, which describes field theory, and otherwise yields the same result as Huygens-Fresnel but absent of the infinite points. Because in real life, those points are a way for use to measure and create the effect with numbers.

So, while diffraction is defined as a wave curving around an corner, in reality it is a series of constructive and destructive interference working together to create an illusion that we see.

At the wavelengths that our eyes are sensitive to, we do not encounter diffraction. However, our instruments can. Small apertures on cameras interacting with the extremely small photo sites on the sensor creates an environment for diffraction, which results in a slight scattering of the individual wavelengths, and renders haziness in the image. This occurs around the f16 aperture of a lens and worsens the smaller the aperture goes.

Because an aperture is a 3D object and not a flat plane, the blade edges becomes an extra point of diffraction interaction for the light. And at smaller apertures, this brings those diffracting waves closer together causing interference and generating an Airy disk pattern, as opposed to a point of light. Thus light that should be hitting one pixel, is now hitting multiple pixels, causing a hazy image.

The smaller the phorocytes on the sensor, the more susceptible to diffraction your image will be. This inherently creates a limitation for camera sensor resolution. For more resolution, we must move to a larger sensor, not a more density.

The common misconception is that the image to the right is in itself diffraction. When you google "diffraction", this image or similar appears.

It is understandable because it is the most visual and bombastic effect of diffraction. But the image itself is an interference pattern achieved when two diffracting waves overlap.

This effect is achieved by creating at least one void and one edge on either side so the resulting diffracting waves may intersect. The void can be a hair or wire, two slits or holes in a thin surface. The smaller the void, the wider the pattern on the screen and easier to resolve with the eye. The larger the void (or further the slits), the more the pattern will blur over itself.

The redirected waves will intersect with each other and interfere constructively and destructively. The dark spots are not destroyed, but instead re-allocated to the bright regions. Yes, the bright regions are brighter. So the luminous output hasn't changed, and the law of conservation is unbroken.

INTERFERENCE PATTERN