03 - Bucket of light: The physics behind photos

Think for a second… how much light is required to create a photo? Can the amount of light be quantified?
The speed of light has been famously known as C in physics and is 299 792 458 m/s. Since light is a continuous source of energy there is a volume that can be associated with it based on the surface area.

The volume of light required to create a photo on a sensor is a CONSTANT value [lets call  VOLUME_LIGHT] and can be kept in a bucket

VOLUME_LIGHT[Constant]= Surface Area X Height

is also equal to

VOLUME_LIGHT[Constant]= [2* Surface Area]   X   [ Height / 2 ]

Summary: To create a photograph a constant volume of light is required and the same volume can be captured by different types of buckets as long as the volume is same.

Lets peek at the formulae again

VOLUME_LIGHT[Constant]= Surface Area X Height

When written in terms of height as “distance travelled by light”

VOLUME_LIGHT[Constant]= Surface Area     X       [Speed of light   X    Time To cover the distance or height]

Speed of light being constant

CONSTANT= Surface Area          X         Time to cover the height or distance

Now relating back to previous posts,

• Surface area is nothing but the Aperture of the lens which allows the light to flow in
• Time to cover the distance is nothing but the shutter open time or shutter speed

CONSTANT = Aperture Value  X  Shutter Speed

Means given sensor requires a certain amount of light to take a photograph, the aperture and shutter speed can be adjusted to allow the required light to reach the sensor. A combination of values can be used for these 2 parameters (different types of buckets). E.g. if shutter speed is reduced then aperture can be increased and vice versa to allow the same amount of light to take the photograph.