How fast does light travel when I turn on my lamp?

[texasH53D]

Today I was sitting at my desk where I volunteer and it was kind of slow so I started messing with my desk lamp. I wondered how fast light travels from the bulb to the desk surface, but I didn't know.

What I want to know is about how fast does the light travel to hit the desk when the light bulb from the lamp is about 12 inches above the desk?

How fast does it take for my eyes to see that light?

And there was even a sort of small rainbow in the circumference of the light, where light meets shadow, why is that?

Also, I blocked the bulb with my hand and I would separate and close my fingers really fast a couple of times (well I guess not that fast, but as quick as I could), how fast does light take to reach the desk then?

I know these are weird questions but I'm curious to know!

 

[Mordred]

honestly, you couldn't google the speed of light?

http://en.wikipedia.org/wiki/Speed_of_light

$c\ =\ 2.99792458\ \times\ 10^{8}\ m\ s^{-1}$. By the way the rainbow is due to refraction, think of a prism. It would take longer for your brain to register the light that hits your eyes than it would for the light to reach your eyes from the lamp. Also your eyes can only register changes at a limited frequency. If I recall its approx 60 hrzt. Your TV takes advantage of this when it changes the image

 

[Bandersnatch]

the lamp is about 12 inches above the desk

how fast does light take to reach the desk then?

Plug the speed of light and the distance(in metres) into the equation for speed: V=dt, and after a bit of elementary algebra you'll get almost exactly 1 nanosecond.

To visualise how short a period of time that is, if your body were to live as many nanoseconds as your life expectancy is in seconds, and assuming you're about 20 now, you'd die in less than two seconds, three if you are to live past 100.

Incidentally, 3 nanoseconds is about as much as one cycle of modern commercial processors(i.e., a 3GHz processor), which should help you appreciate how fast these things are.

 

[adjacent]

To visualise how short a period of time that is, if your body were to live as many nanoseconds as your life expectancy is in seconds, and assuming you're about 20 now, you'd die in less than two seconds, three if you are to live past 100.

Incidentally, 3 nanoseconds is about as much as one cycle of modern commercial processors(i.e., a 3GHz processor), which should help you appreciate how fast these things are.

More precisely, one nano second is $\frac{1}{1000000000}$(One billionth) of a second! Which means during one second, there are 1000000000 nanoseconds.So imagine how fast 1 nanoseconds would pass.

 

[sardar]

I can provide some answers to your questions about the speed of light. Light travels at a speed of approximately 299,792,458 meters per second in a vacuum. However, the speed of light can vary depending on the medium it is traveling through. In air, light travels at a slightly slower speed of about 299,702,547 meters per second.

In terms of how fast the light from your lamp reaches the desk, it would take approximately 1/299,702,547 seconds for the light to travel 12 inches (or about 30.48 centimeters) in air. This means that the light would reach the desk almost instantly, as the speed of light is incredibly fast.

When it comes to seeing the light, the process is a bit more complex. Once the light reaches your eyes, it enters through the cornea and passes through the lens, which helps to focus the light onto the retina at the back of your eye. The retina contains specialized cells called rods and cones, which are responsible for converting light into electrical signals that are sent to the brain. The brain then interprets these signals as images, which is how you see the light from your lamp.

The small rainbow you saw at the circumference of the light is known as a diffraction pattern. When light passes through a small opening or around an object, it bends or diffracts, creating a pattern of colors. This is why you saw a rainbow-like effect around the light.

Finally, when you blocked the light with your hand and quickly opened and closed your fingers, the light would still reach the desk at the same speed as before. However, your hand and fingers would be blocking and unblocking the light, creating a strobe-like effect that may make it seem like the light is moving faster or slower.

In summary, the speed of light is incredibly fast and it would reach the desk almost instantly when you turn on your lamp. The process of seeing the light is a complex one that involves the conversion of light into electrical signals in the retina. The rainbow effect and strobe-like effect you observed are both due to the properties of light and how it interacts with different objects. I hope this helps to answer your questions and satisfy your curiosity!