Light Torch
Why does light intensity between a light source (like torch) and a target decrease as distance is increased?
Can anyone explain using scientific reasoning? sources would be appreciated as well.
Inverse Square Law:
Stand a few steps from a wall and shine a flashlight at it. Look at the bright spot the flashlight makes on the wall. Make some observations of the spot. In particular, how big is the spot? How bright is it? When you make your observations, be sure to look at the whole spot of light, not just the bright center region.
Now walk away from the wall a few more steps, while still shining the flashlight at the wall. How has the light spot changed? Again, look at the entire spot of light. You should notice that while the central region of light hasn’t changed brightness much, the spot as a whole has gotten dimmer. You have probably also noticed this effect when you’re sitting at a campfire and your friends walk up to the fire–the closer they are to the fire, the brighter their faces become. In fact, the same principle applies to what your friends see–the closer they are to the fire, the brighter the fire appears to them.
Why does a light source (such as a flashlight or a campfire) seem dimmer the farther away it is? The reason is that the light coming from the source spreads out in all directions. You can see a campfire no matter what direction you are looking at it from–even if you are flying above and look down! In a flashlight, the body of the flashlight blocks light in some directions and redirects it out the front (using “mirrors”–the shiny silver coating you can see looking into a flashlight), so it seems to be shining in only one direction. But the light bulb inside the flashlight, like the campfire, shines in all directions.
You can see that the light from the flashlight does in fact spread out by looking at your observations from the experiment you just did. You should have also noticed that the spot got larger, not just dimmer, as you backed away from the wall. The same amount of light was now spread over more of the wall, so the spot appeared dimmer. A similar idea applies when you’re spreading jelly on a peanut butter sandwich. You start with a large glob in the middle, which is very thick but covers a small amount of the bread; when you spread the glob out to cover the entire slice of bread, it gets much thinner. The light, like the jelly, is “thinner” when it covers a larger area.
How quickly does the light get dimmer? For instance, in the experiment you just did, how much dimmer is the light on the wall when you are twice as far away from the wall as you were initially (i.e.: four steps away instead of two steps)? Try this: tape a large sheet of paper on the wall where you will be shining your flashlight. Stand about two steps from the wall and make sure the light shines on the paper. Have a friend trace a circle on the paper around the edge of the spot of light. You should then back up two more steps, and have your friend trace a circle around the light again. Take down the sheet of paper and look at the two circles. Is one twice as big as the other? Four times? You can cut out several circles about the same size as the small circle and see how many it takes to cover the large circle. You should need about four. (Or, if you draw the circles on a large sheet of graph paper, you can count how many squares are in the small circle and then the big circle. There should be about four times as many in the big circle.)
Therefore, if you are twice as far away from a light source, it should appear one-fourth as bright. Scientists call this “the inverse squared law.” In math terms, you can find the relative brightness of two objects by comparing their relative distances to you, squaring this value, and then inverting it. (Twice as many steps from the wall (4 versus 2) squared is four, and inverting four gives one-fourth: the flashlight is one-fourth as bright on the wall when you are four steps away as when you are only two steps away.)
|
|
GrippIt! Light Kit Flashlight $15.84 The GrippIt! Light Kit is the most versatile flashlight youll ever own. Enjoy ultra-bright illumination and hands-free flexibility while working on household projects, fixing your car, or even lighting a room or campsite. |
|
|
Streamlight Nano Light Key Chain Flashlight $15.99 Truly tiny, the Streamlight Nano Light is a weatherproof, personal flashlight featuring a 100,000 hour life LED. The light includes a non-rotating snap hook for easy one-handed operation when attached to a keychain. |
|
|
Streamlight Task Light 2 AA Flashlight $25.49 Have light wherever you need it with this Sreamlight task flashlight. This handy flash light is powered by just two (2) AA alkaline batteries. |
|
|
Emerson Multi-mode Night Light with Flashlight $27.49 Never be left in the dark with the versatility of the Emerson Multi-Mode Night Light with Flashlight! Get the best of both worlds with this perfect combination that is great for emergencies or when you simply need light during the night. |
|
|
Triarch International Olympian 2-light Torch Bronze Flush Mount $135 Evoke the divine with this elegant design from Triarch International. Torch bronze finish creates a classical motif for any lighting decor. |