How does intensity change with distance

There is an inverse relationship between distance and light intensity - as the distance increases, light intensity decreases. This is because as the distance away from a light source increases, photons of light become spread over a wider area. The light energy at twice the distance away is spread over four times the area.

The light energy at three times the distance away is spread over nine times the area, and so on. Notice that as the distance increases, the light must spread out over a larger surface and the surface brightness decreases in accordance with a "one over r squared" relationship.

The decrease goes as r squared because the area over which the light is spread is proportional to the distance squared. If M31 is moving with respect to the Earth, you should be able to see a change in its apparent brightness if you take two measurements at different times.

Measuring this change would allow you to calculate its speed. QED describes how light and matter interact, and is the first theory that fully reconciles quantum mechanics and special relativity. QED calls for the upholding of the inverse square law with reference to light because photons have a vanishing pole mass.

The prediction holds with other massless particles, and explains the inverse square law of gravitational force. Newton also dabbled with the Inverse Square Law in his study of gravity, where he measured the periods and diameters of the orbits of Jupiter and Saturn. He found that the forces on Jupiter and Saturn, exerted by the sun, were proportional to the inverse of the distance squared. Although the inverse square law applies to sound, gravity, and electric fields, Bullialdus focused on light to test this theory.

He did this by showing that the intensity of light I at a given distance from the origin of the light was the power output of the light source S was proportional to inverse of the squared distance.

This did not only explain that light decreases over a distance, common knowledge at the time, but that it decreases at a specific proportion to the inverse of the distance squared. This works because the Power output of the light source has to be divided by the surface area it has to cover. The aim in this investigation is to determine whether the intensity of light decreases as a proportion of the inverse of the distance squared, and I hypothesise that the real-world results will reconcile with the math.

If I measure the intensity of light at a given distance of r, it will decrease proportionally to the inverse of the distance squared. Controls: ambient light in the room, wattage of bulb, increment of measurement, reflective surfaces in the room, reflective potential of my body, angle of lightbulb, height of lightbulb.

I had to use multiple conversions and calculations to reconcile my data.