Total Internal Reflection in Water "Bucket of Light"

A beam of laser light can be trapped inside a stream of water by suffering total internal reflection-the aquatic equivalent of a fiber optic cable. In our setup we have a 2-liter soda bottle with a hole cut into the side. The bottle is filled with water and a few drops of milk. A 5 mW HeNe laser is brought up to the side of the bottle, so that the beam exits the bottle via the hole. The laser light undergoes total internal reflection as the stream of water falls into the bucket in a cohesive stream.
Some of you may notice that the white bucket glows with the same color as the laser light, even after the water has stopped flowing into it! How can this be? Does the light keep reflecting around inside the bucket? Did we somehow find a way to violate conservation of energy? This part of the demo is a trick, of course: a network of red LEDs line the bottom of the bucket!
For more details on how we set up this demo, see
sciencedemonst...

[@mighty_her4784]

you had me with the LED! hahaha, great demonstration thank you!

[@iam_gabru_ravidassia5529]

What is your Instagram id

[@octahedralnuke8917]

nvrgonagiveuup

[@Wnsgur0115]

That light of the bucket keeps my attention over 10 min (double time of this video), What a trick!

[@ccc3]

I kept scratching my head as to what was going on when the bottom was revealed and then realized this was posted on April 1. Well played, Harvard, well played

[@jeffdodson]

i like the little magic trick at the very end, Daniel! :)

[@DanielRosenberg]

Thanks! It’s my own design, with a FET that switches on the LEDs when the water covers two nickel foil strips. I’ll put that on the list of behind-the-demo videos to make.

[@ishanr8697]

With my students I normally use a measuring cylinder filled with water impregnated with a bit of pink highlighter fluid and a green laser. It fluoresces yellow and looks fantastic!

[@AxcelleratorT]

Well played! Thumbs up!

[@maureenedonovan9935]

Amazing. So much to learn.

[@fowlfables]

Who else needs to pee now?

[@SIMARON-TV]

amazing , thanks for the experience

[@Muonium1]

That soda bottle looks about as 80s vintage as that HeNe!

[@NatSciDemos]

you are correct!

[@stevephillips73]

If the light is completely trapped inside the stream of water, why do we see the red color of the laser in the stream? That means some of the light is escaping from the stream, doesn't it?

[@NatSciDemos]

Yes you are correct, to make the demonstration more visible to the audience we add a couple drops of milk to the water so that some of the light scatters off to the side of the water flow.

[@sukhps]

nice observation

[@HilliIndustries]

Darth Vader peeing...

[@RahulKumar-xp6mc]

Wow beautiful phenomenon

[@kumarrishabh7042]

Just mind blown

[@WhoFramedRogerRabit]

I came here to explain my job to people, and now I have to pee.

[@268TERI]

Cool! Thank you!

[@zero-bl1fq]

The light is still in the bucket?...woww

[@SkyDarmos]

Why is the water still shining after landing in the bucket? Does that mean we can store light in a bucket like that?

[@NatSciDemos]

No, that part of the demo is actually a prank-the bucket is illuminated by LEDs that we wired to the bottom of it to make it seem like the light is stored in the bucket, in violation of conservation of energy. The illuminated stream of water, however, is a real phenomenon.

[@awar4300]

Wow... thanks a lot

[@dailyscience......77]

Wow ,super activity

[@Itzblu777]

5 year old me at 2am at my friends birthday party sleepover after I drank all the red glowsticks

[@atlantaguitar9689]

So now we can route lasers inside of water - just when we thought squirt guns were safe toys.

[@VOIBLE]

This is beautiful. Can I use a part of this footage especially from opening the bottle cap to water flowing down? Of course, credits will be given on video and description.

[@ramizr]

Lmao this is enough to fool my non-science background friends 😂

[@kricketflyd111]

I am going to create a Hindu meditation spa with showers and falls that do that.

[@eternallove6798]

Are those lights at the bottom of the bucket and why are they there? What purpose do they serve? I have questions and need answers.

[@NatSciDemos]

Yes there are battery powered LEDs that automatically turn on when water is added to the bucket. Their purpose is to provoke questions and discussion about wether the laser light will keep reflecting around inside the bucket after the stream of water has stopped, resulting in a "bucket of light."

[@danatheus264]

They prompted questions in my mind for sure! So does the light continue to reflect in the water in the bucket?

[@odettemanlove1759]

@@NatSciDemos So is the answer yes since the color didn't change?

[@pradeepsharma8718]

After the bottle got empty , why water in bucket is glowing sir.

[@kenmiles32]

It is a prank.Check the date of uploading

[@sto2779]

We need to see how far the TIR of the laser in the water goes down.

[@Kristinapedia]

Now I gotta pee.

[@AliVeli-gr4fb]

very cool

[@fasligand7034]

why is the bucket still lit up in red after the experiment?

[@mjk0104]

You should read the description :)

[@fasligand7034]

@@mjk0104 haha indeed, or watch the video to the end, my bad!

[@eternallove6798]

What are those in the bottom of the bucket and why?

[@artsmith1347]

Where are your laser safety glasses?

[@allencampbell3350]

Anybody else need to pee now?

[@LearnWithFardin]

What?? 1:27 Is there a source of light inside the bucket!!

[@Inndjkaawed2922]

Awesome

[@joanrodriguez4145]

Why does the water pour out of the hole in the bottle only after the cap is removed?

[@Kristinapedia]

Air flow. Ever pour Any liquid out of a bottle or jug and it goes "glug glug glug" ? That’s Because there's not enough air going in to allow the liquid to come out. Put a straw into the bottle so the inside end of the straw is an air pocket and then the liquid will flow out smoothly. Science 101.

[@johnblair1119]

@@Kristinapedia science 1001

[@edgarntondeisingoma2587]

Someone explain the ending part where the bucket is shining

[@NatSciDemos]

The flashlight in the bucket is a prank to make it seem like the laser light has been captured in it.

[@BrianThomas]

Natural as the water runs out the pressure is reduced. Question: even though the light source maintains the correct angle of acceptance. Why does the light follow the flow almost all the way? I noticed at the end when the light falls out of the water stream. Looks very nice in slow motion. Is this because the angle of reflection is grater than the angle of refraction?

[@NatSciDemos]

The short answer is that every time the laser light inside the stream of water encounters the inner wall of the stream (i.e. the water-air interface) the angle of incidence with that interface is less than the critical angle needed for total internal reflection. For more explanation, see hyperphysics.gsu.edu/hbase/phyopt/totint.html and sciencedemonstrations.fas.harvard.edu/presentations/bucket-light

[@johnnytarponds9292]

LMAO! Excellent!

[@marcodev3375]

Not totally reflected. I still see light leaking out from the water flow. If totally reflected, we shouldn't see the light, right?

[@NatSciDemos]

To make the demonstration more visible we added a few drops of milk to the water, which scatters the light from within the liquid.

[@fadli1987]

Lol.. i got prank

[@akhilat3007]

👏👏👏👏👏

[@darklove6251]

What would happen to the laser beam if the bucket was a fish tank full of water

[@NatSciDemos]

In that case the laser light could reach the bottom of the tank and reflect (at least partially) off of whatever's there.

[@darklove6251]

@@NatSciDemos that’s pretty cool that means light can be completely redirected. What if you shined a bunch of lasers at the hole in the top.

[@karenstein9468]

Why the "few drops of milk"? Is that just to add a little opacity so the color show up better?

[@NatSciDemos]

Basically yes--the milk scatters the light off to the side so that we can see it better.

[@jamieparker3317]

Go to the bathroom before watching this.

[@leozendo3500]

1:29 why is the bucket still glowing red?

[@NeetchianQueen]

Ha Ha NICE!

[@dimassmirnoff6378]

Наука епта.

[@yellowwtangg]

Neon piss

[@MrAirpilot1]

Why the LED trick in the bucket? A serious experiment marginalized by showmanship. Too bad the "scientist" isn't serious...

[@soundpainter2590]

Happy April fools day !!

[@JustinJones_now]

Diagnosis: hematuria.

[@Nuy48]

Nice

[@maxnguyen3503]

Oooof...That water pouring out of the bucket looks like knowledge pouring out of my brain

[@MartinALopez-gz5kf]

Girl really? Why would you make you question the light inside the bucket. I was pissed because I actually thought for one hot second light actually stayed in the bucket. LMFAo

[@tanishqkumar4016]

Haha, this isn't the concept of total internal reflection, this is the glowing water in real! 😀

[@Simonjose7258]

You should have used a yellow laser.

[@Curiousitydriven]

Why that bucket is glowing red after water flow stopped

[@NatSciDemos]

we hid a flashlight in the bottom of it

[@Akel-di4kx]

Who's from alan walker ?

[@azimalif266]

Is it possible to use bent acrylic tube to redirect sunlight to a shaded place?

[@NatSciDemos]

Yes.

[@usman710]

Trapping light near indefinitely will be one of the biggest achievemnts of mankind

[@belavarplaniie8933]

Elegant presentation!

[@Buzzhumma]

Thank you

[@gurdevsingh5637]

Good video

[@vanotank1645]

НАХУЯ!?

[@leonardtramiel8704]

The red LEDs in the bucket ruin this video. Faking things is NOT a good way to do science demos!

[@tonyazrael8223]

What's wrong with a little humor in a science demo? Don't be lame.