How to Listen to Light




About: I've built some weird stuff over the years, but most of that stuff has remained unseen by the world outside of me and a few friends. But then one day, one of these friends, he says to me, "Hey Jack, you sho...

The human eye cannot discern flicker with a frequency greater than roughly 30 Hz. A light turning on and off faster than this does not appear to be turning on and off. Instead it appears to have a constant intensity to the eye.

Human ears however are much faster, that is, better able to perceive a signal changing quickly in time. The human ear can detect frequencies from roughly 20 Hz to 20 000 Hz, provided those frequencies arrive as sound.

Now suppose there were an easy way to change light of time-varying intensity, into sound of time varying intensity. Then you could "hear" light that was flickering too fast for you to see it.

The humble silicon solar-cell can convert a time-varying light signal into a time-varying electrical signal. This small electrical signal can then be fed to an audio signal amplifier and converted into sound.

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Step 1: Parts:

1 audio amplifier (Radio Shack Catalog #:277-1008)
1 1/8-inch (3mm) headphone plug, can be mono or stereo
1 small Silicon solar cell with approximately 1 cm2 in area
1 1/2-inch PVC pipe cap
some wire, solder, epoxy, black paint, etc.

Step 2: Assemble and Wire Up the Light Sensor.

The wiring diagram, first pic in the stack below, shows how to wire the solar cell to a mono audio plug, or how to do the same trick with a stereo plug. Basically for the case of a stereo plug, it is wired up so that electrically it's a mono plug.

In words the tip of a mono audio plug is named "tip", and the ring shaped conductor behind the tip is named "ring". I have connected the positive side of the solar panel to tip, and the negative side to ring. In the little picture in the wiring diagram, ring is labeled with a "1".

The second pic in the stack below shows the actual wiring itself.

You might be wondering what kind of dark magic was necessary to turn that messy box of solar panel shards, shown in step one, into the pretty little perfect circle which will fit neatly inside a 1/2-inch PVC pipe cap. The answer is shown in step 3, sort of, and step 3 is optional.

You see, working with little solar panel shards is kind of a pain in the ass, and I don't recommend you do this unless
(a) You're a masochist - that is, you like pain and frustration
(b) You don't have a pre-made solar cell that will neatly fit inside the light shield

By the way, the "light shield" is another name for the PVC pipe cap. It's intended to block out stray light. In step 4 I paint it black, for extra super-duper light blocking ability.

Step 3: (OPTIONAL STEP) Cutesy Recycled Circuit Board Circles!

Uh... lets see... This step involved: De-soldering parts from a junk circuit board. Cutting off a piece of depopulated board with a radial arm saw. Using a hole saw to cut out some little circles. Then attaching the circles to a bolt, and loading this bolt into the drill press, for purposes of slimming down the circles, decreasing their radii by placing a file against their edge, while the drill press is spinning them. Then sanding the paint off the little circles by rubbing them against a sheet of sandpaper held to a clipboard.

Then I carefully broke off a piece of solar panel shard. Then carefully soldered it to one of the little circle boards I made, and then I soldered some wires to the appropriate places on the panel.

Verily, this is the story of the genesis of the little circular solar-cell board seen in Step 2.

Step 4: Gluing and Painting

The purpose of the little PVC pipe cap enclosure is twofold.

One is that it offers some mechanical protection for the solar cell, which is kinda delicate. So the board and wiring are glued in place with epoxy.

The other purpose is to block out light coming from most directions. So I do like the old Stones song suggests, and paint it black.

Step 5: Test the Light Sensor (in DC Mode)

This is just a quick test to see if the light sensor is working, not wired up backwards, etc.

I switch my multimeter in small-dc-current mode, then connect the probes to the audio plug and see what happens.

It looks like the light from the fixtures above is causing the solar cell to produce about 20 microamps of current.

This is good.

Step 6: Plug It In. Turn It On.

The plug from the light sensor goes to jack on the audio-amplifier labeled "INPUT".

Then turn the turn the little gain/volume knob on the side to turn it on.

Also important: the amplifier should have a 9V battery installed in it, or a power source of some kind.

Step 7: Various Light Sources

Many artificial forms of light vary in intensity with frequencies in the audio region. Some examples include incandescent light bulbs, LED displays on microwave ovens and other kitchen appliances, computer monitors, TV-remotes, etc.

Provided you've put everything together correctly, you will hear some kind of sound coming out of the amplifier when the solar cell is receiving light from a time-varying source.

In case all you have are non-varying "DC" sources of light, like sunlight, try waving your hand back-and-forth in front of the solar cell, quickly blocking and unblocking the light reaching it. This should produce a soft clicking noise at each dark-to-light, light-to-dark, transition.

Step 8: LED "tea Light" Candles Play Music for Some Reason


Just place the light sensor near the LED candle and in many cases you'll hear cheap electronic music coming out the amplifier. The one in the picture below plays "Fur Elise".

It is also possible to tap into these little LED candles and listen to the music via wire, as shown in this instructable:

I suspect that the reason for this is that those mass-produced music chips also work well as a source of time varying "flicker". That is, this signal looks like flickering light when driving an LED. The same signal sounds like cheap electronic music when driving a speaker. The same chips are used for both, or at least that's what I suspect. If anyone can confirm this hypothesis via a source in the Chinese knick-knack industry, please comment.

Step 9: Some Captured Sound Samples

For those of you who asked for them, I captured some sound samples from the light-to-sound project.  These are uncompressed .wav files, sampled at 44 KHz and 16 bits per sample.  Each is roughly 10s in duration. 

I realize downsampling to a lower sampling rate, and/or encoding to a compressed format  (like mp3) would certainly save y'all some space, and download time.  But this might also introduce artifacts into the sound that weren't there in the first place, and I'm trying to be scientific about this, sorta.

This additional step was added on 20 Nov, 2009, about a 1+1/2 years after the bulk of this instructable was published.  Sorry it took so long. I don't have a good excuse for this.

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    43 Discussions


    4 years ago on Introduction

    Mr. Jackalope-z :-),

    I looked at your name and immediately saw the connection - THEN noticed the picture - very clever!.have you been to the Dakota's? That's the only place I've EVER heard of or seen a "jackalope!" Very, very good!!!

    2 replies
    Jack A LopezLisaL14

    Reply 4 years ago on Introduction

    I think jackalopes can be found all over the North American continent, and typically dead specimens are much more common than live ones.

    For example, at 0m+40s into this video,

    Rob Zombie shows us a mounted jackalope, just the head, at his house in California.
    But this jackalope was not native to California. Rob says he ran over it with his car, while driving through Wisconsin.

    In response to your question, I have never been to North Dakota, or South Dakota. Although I have been to Montana, which I think borders one of those Dakotas, probably the North one.


    8 years ago on Introduction

    Would be Very Interesting to listen to Modulated Laser Light.

    Maybe even have 2 way line-of-sight laser communication.

    2 replies

    Reply 4 years ago on Introduction

    Alaska and Hawai'i are states in the USA, there are only 50 of them despite what some of our politicians may think.
    I have, for periods of time, lived and worked on some 60 islands like Adak, The Big Island, Moloka`i, Maui, Lana`i, Oahu, Kawa`i and Ni`ihou. Out of all the islands I have been to Hawai'i MoBettah Sistah.
    Hawai'i will always be my home where ever I happen to live.



    11 years ago on Introduction

    I did this once a IR remoted played part of the twilight zone theme song! it is landing!

    1 reply

    8 years ago on Step 9

    Thanks...I had really wanted to record the sound my light listener made but had no time...

    2 replies

    Reply 9 years ago on Introduction

    Now people can sell battery powered tea light candles for privacy concerns, to help confuse laser window monitoring bugging equipment!

    Although it won't work well against the good optical bugs because a technician will just tune out the frequency of the tone generated tea light music.

    Can I get an LED that plays the theme from "Get Smart" please?
    Dunt da daaa DA!
    Dunt da daaa Duh!


    9 years ago on Introduction

    I made one of these with a broken solar light. I figured it would have a nice enclosure and well, it was the only panel I had in my house.

    2 replies

    That works. Or at least I'm guessing that it worked... Have you found any interesting sounding light sources?


    9 years ago on Step 8

    Actually you are half right.
    They are prob using the music chip as a template that produces a smooth flicker cycle they have tons of.
    The second part is because our brains naturally like certain sounds, patterns and tones. We change them over time, but there is a larger portion of these tones and patterns in classical music. I believe Bach is the winner in that category.
    In that way flicker would cycle would be more pleasing.


    9 years ago on Step 2

    hey, would it be possible to use a solar panel from a calculator? would i just hook up the cables on that directly to the 3mm plug?