I’m going to start this post off in a photographic perspective, as photography is all about light.

According to the Sunny 16 rule, the optimal shutter speed on a bright sunny day will be the reciprocal of the ISO if the aperture is held at f/16. As I use ISO 200 for most outdoor bright sunny day shots, the shutter speed would be 1/200 seconds at f/16.

From personal experience, the optimal shutter speed in an average incandescent bulb-lit room, with no outside light source, is about 1/25 sec at 1600 ISO and f/5.6 aperture (give or take).

These are purely rough estimates and of course would vary slightly based on location, etc, but that’s beside the point. Let’s take a look at how drastic of a contrast these two lighting conditions are.

The difference between 200 and 1600 ISO is +3 stops. From 1/200 to 1/25 shutter speed, +3 stops. From f/16 to f/5.6, +3 stops. This gives a total of +9 stops of brightness between the average sunny day and the average room lit with average-intensity incandescent light. Translated into layman terms, that’s 512 times brighter (a stop is a doubling of brightness).

512 times brighter. Think about that for a second.

(Edit: Now that I come to think of it, the average shutter speed for an incandescent light bulb lit room is more like 1/10 sec or so. That’s a +/- 10 stop differential… 1024 times.)

Now think about how much incandescent power it takes to light a room to “decent” levels (which is still probably at least half a stop away from what I’m referring to). Then think about how little of the sun’s energy from 93 million miles away actually reaches any given location on Earth.

This enormous discrepancy can be accounted for on many levels. First off, energy sources. The Sun is fueled by fusion reactions inside its core, which release, well, a lot of energy, a good portion of it light energy. Light in light bulbs, on the other hand, is “created” when internal resistance and the associated heat energize electrons to their excited state in the bulb’s filament. These electrons then fall back to their ground state, releasing light energy while doing so. Secondly, the Sun’s energy efficiency is much greater. In fact, according to Wikipedia light bulbs “emit only around 10% of their energy as visible light and the remainder as infrared [radiation]”.

In summary, sun = win; light bulbs = fail.

Just some food for thought…


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