For example, I’m sitting on my front porch which overlooks the town. Miles away I can see streetlights, signs, etc. How does the source project light to my location, yet doesn’t illuminate my location?
Holy moly friends, thanks for the awards and stuff. I didn’t think this question would spark so much interest, lol. I am thoroughly grateful for all your replies.
In: Physics
The concept that comes into play here is called intensity. What you refer to as illumination would mean that the light in your area is high intensity. Intensity can be measured in photons per unit area per second. If you consider a point which is giving off photons in every direction, they will all travel away from the point at the same speed. If you know the frequency of the light and the power being supplied to the source, you can calculate the exact number of photons being emitted per second. You can then imagine that all of these emitted photons travel outward at the same speed in a shell and as they travel outward, that spherical shell of light expands. You can then assume a radius from the source and the area upon which photons would be incident. Take a ratio of the incident area on your eye to the total surface area of the shell, then multiply the emitter’s photons/second by that number. That is the number of photons per second which are striking your retina. You could also multiply that ratio by the emitter’s power output to obtain the total power delivery to your retina. There are a bunch of different ways to calculate varrying definitions of intensity, like irradiance, radiance, luminous intensity, etc, but they’re all relatively similar. Generally, the higher these various numbers are in your eye, the brighter a source seems to you.
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