Diffused Light and its Intensity
Foot candles vs light travel distance relationships
The relationship between foot candles and light travel distance mainly depends on the type of lighting being used, as well as its intensity. The further away the light source is from the subject, the less intense it will be conversely, the closer the light source is to the subject, the more intense it will be. However, there are other factors such as brightness, color temperature, and beam angle that can also affect the intensity of the light. Additionally, the shape and size of the scene play an important role in the amount of light available for a given distance. Thus, when considering all these elements, a photographer should pay close attention to the foot candle vs light travel distance relationship to capture the desired image.

What is Tim Kang’s theory?
Tim Kang’s Theory of Light Photography is a systematic approach to lighting photography that focuses on the intensity, color, and texture of light. It emphasizes that the manipulation of the three elements of light must be carefully considered when taking a photograph in order to achieve the desired effect. According to Kang, there are four components of light – direct light, diffused light, reflected light, and ambient light – and each component has its own distinct purpose in a photograph. Therefore, when combining these elements, a photographer should pay attention to the geometric relationship between them to capture the desired image. Additionally, he also emphasizes that the direction of the light should be determined beforehand to accentuate the features of the subject and bring out their creative beauty.
Inverse Square Law of Light Diffusion
The inverse square law of light diffusion states that the intensity of illumination from a point source is inversely proportional to the distance squared from the source. In other words, the farther away from the source you get, the darker it gets. This phenomenon is particularly important for photographers and cinematographers, as it helps them understand how the amount of light reaching their subject changes with different distances.

Where, I is the intensity of light in foot candles and d is the distance between the light source and the subject.
To understand the inverse square law more clearly, we must look at some basics of physics. Light travels in a straight line and follows an inverse square law due to its nature as an electromagnetic wave. This means that the intensity of light is proportional to one over the distance squared. As distance increases, the intensity of the light decreases according to this proportionality. The same principle is applied when calculating the force exerted by gravity between two objects, resulting in the famous inverse square law of gravity.
In photography, the inverse square law of light diffusion can be used to help create beautiful, creative images. Different lighting conditions require different levels of light, and understanding the inverse square law helps photographers balance the amount of light that reaches their subject. For example, photographers may want to place their light source very far away from their subject if they are shooting a landscape photo. This will cause the light to be much softer and more subtle, as the inverse square law dictates that the further away the light source is, the less intense the light will be. On the other hand, if the photographer is shooting a portrait, they might want to keep their light source close to the subject. This would result in stronger, harsher light as the inverse square law would mean that the light will be more intense the closer the light source is to the subject.
Overall, the inverse square law of light diffusion is an important concept to understand for anyone interested in photography. By understanding how the amount of light decreases with increasing distance from the source, photographers can better control their lighting, creating the perfect environment for their subject.
To understand the light practically we should look at the soft light source and the object kept at distance away from . If the light source is 1 feet away from the source of light, source will cover 1 square feet area. Same light at 2 feet will cover 4 square feet area and at 3 feet it will cover 9 square feet of area.

The coverage of light follows the equation above, the coverage is proportional to square of the distance between the subject and the source of the light.
The intensity of light can be measured with the foot candles and lumens of the light source falling on the subject. As we have seen before that the intensity of the light reduces by square of the distance. At 2 feet the intensity of the light will drop by ¼, at 3 feet the intensity of the light drops by 1/9 and similarly at 4 feet the intensity drops by 1/16 of its original value.
If we look at the light sources and their intensities in terms of lumens, we need to find out the lumens first for each light source. But before that the measures for foot candles needs to be defined. The diagram below defines the foot candle definition most clearly.

Considering the light sources that exists, we have the lumens values for each type of light source as shown in the table below:

In the table above, if we look at 100 watts incandescent lamp, which has the intensity of 1600 lumens. At 1 foot distance the intensity of a 100-watt light is 1600 lumens.

This 4304-foot candles are roughly equal to 2 stops. This reduction of 2 stops needs to be accounted for when this distance is in place. I.e., to increase the intensity of the light on the subject to its full needs to be brought closer to light source by at least half the distance of 1 foot (~1.5) candles are roughly.