The Fluorescent Light Organ

I was contacted recently by a fellow named Doug Booth Jr. regarding an obscure type of music-triggered light display using regular fluorescent lighting tubes. Similar to the classic "color organ" of which there are many different types, the Fluorescent Light Organ (FLO) uses the slightly differing electrical characteristics of a set of fluorescent tubes wired in parallel to produce an interesting display.

*****Warning! High voltages present inside some of the circuits posted here can injure or be fatal, and may still be present long after power has been removed from the device. Only work on or modify vacuum tube amplifiers or other high voltage equipment if you have experience with high voltage electronics and are familiar with proper safety procedures. If you are unfamiliar with this type of electronics, please be safe and find someone who has the qualifications to do the work for you. Glass fluorescent tubes contain mercury, are fairly fragile, and can be extremely hazardous. Small glass fragments and poisonous substances are released if they are broken. Always handle these types of tubes carefully and keep them away from children and pets. Any experimentation that you do with the information presented here is at your own risk.*****

Doug was kind enough to send me an article that he wrote regarding the FLO, which is presented below:

The Fluorescent Light Organ

Can you imagine a light organ in which the lights are illuminated directly by the energy of the music signal? One in which the musical spectrum is not segregated into x-number of frequency bands, and each musical note has access to every light? One in which the lights present a close approximation in appearance to an actual pipe organ? One which displays an almost infinite array of patterns of light and dark playing across a multitude of parallel fluorescent tubes?

The above is a sketchy description of the Fluorescent Light Organ. It was invented in or before the 1950's and presented in a magazine article around 1956 entitled "The Light Organ." I have added the word Fluorescent to the title to differentiate between it and the multitude of Light Organs which have been invented and developed in more recent years, using anything but fluorescent lamps. This device predates the availability of home computers, so it doesn't require one. Nor does it use frequency selective networks or silicon controlled rectifiers or triacs to control the lamps

This device is not for the faint of heart since it involves High Voltage and dozens of fragile glass tubes. Left alone the Fluorescent Light Organ is eager to provide years of enjoyment, but at a rowdy party it could be Dangerous! I accept no responsibility for anything which happens as a result of anyone reading this article.

One would expect a group of fluorescent tubes of the same type, connected all in parallel to all light up when enough A/C voltage is applied. Well this is just what happens in the Fluorescent Light Organ when it is receiving high-volume audio at its input, but reduce the volume a bit and most of the lamps go black. Some remain lit, according to which ones ignite at various audio frequencies at lower voltage than the others. Since the music continually changes in pitch and volume, the effect is to vary the location and intensity of whichever tubes are lit. The tubes are fixed in place fairly close to each other and there is much dynamic interaction of their electric fields. The display is somewhat dim except at high volume so it is best viewed in almost darkness. During daylight hours The Fluorescent Light Organ is usually mistaken for a white curtain.

Treble notes will light the top (hot) end at the tubes at first and if the note gains volume the light will continue down the tube until it is lit full length. If strong bass music is added it will interfere with the lighting from the treble, causing some parts of the tubes to be dark while the rest of it is still lit as patches of dark dance all over the display. This phenomenon is very transient and beautiful to see. Some people have said this can't happen. It can be demonstrated to appear with certain selections of music.

The Fluorescent Light Organ is a one-of-a-kind instrument. It can be Googled now in April of 2017, and there is no result except other types of light organs. It is controlled entirely by the audio frequencies, volume and rhythm presented to its input. This device became known in a small article by its inventor in an electronic enthusiasts' magazine in 1956. Therefore, there is no computer or controller associated with it. The music controls directly. I have constructed Fluorescent Light Organs with 6 to 40 fluorescent tubes, with 4 foot and 8 foot tubes and they all worked. I do not know the maximum number of tubes which could be connected in a single organ.

DISCLAIMER; Beware! The Fluorescent Light Organ contains high voltages! The fluorescent tubes used are made of very thin glass and will break easily. These tubes contain a high vacuum, and when broken they implode with force, scattering small fragments of sharp glass about for several feet and releasing the tiny bit of mercury which provides the vapor to make the electric arc inside them. The white fluorescent powder coating the glass will also be scattered. It is not known whether or not an imploding tube in the array would cause a domino effect involving all 40 or however many tubes would be in the display- a catastrophe to be sure. I, Douglas Booth, Jr. am not responsible for any mishaps, accidents or malfunctions of any one else's experiments which may result from becoming aware of the Fluorescent Light Organ. Used fluorescent tubes or ones with a burned-out filament work as well as new ones as long as the vacuum is intact and the blackened ends can be hidden.

The Circuit:

The driver amplifier in the original magazine article showed only the output stage which was a single-ended audio amplifier with an audio output transformer or inductive load. No speaker was connected because when the fluorescent tubes fire the audio at this point is distorted. The connection to the array of tubes was made through a capacitor of one microfarad rated at over one thousand volts. It connected directly to the plate of the power output tube, and the other terminal connected to the "rail" across the top ends of all the tubes in parallel. This is high-voltage audio and probably should be carried to the array by a length of RG8 coaxial cable with the shield grounded to the amplifier chassis.

Connect the other end of the shield to the "rail" running across the bottom ends of all the tubes in parallel.

Fluorescent tube sockets could be employed to hold them in the array, but I used them only once when making a portable 40 tube display with 4 foot tubes on squares of pegboard. I found these sockets in an ancient stock sale display at an electronics warehouse for $0.15 each. For all my other organs, except my current one, I just soldered the tube pins to two 12 gauge bare copper wires running parallel across the top and bottom ends of the tubes

The Fluorescent Light Organ which is in my music room now uses 8 foot tubes of the type used in department stores before the LED replacements became available. They have only one pin, 3/8 inch in diameter at each end, essentially neon tubes with white phosphor to glow. I found strips of screen-door constructing material 8 feet long, shaped into a metal box inch across by 3/8 inch thick, back when Sears had everything. I drilled 38 holes in one flat side, 3/8 inch in diameter for my tubes' single pin, spacing them two and three-quarters inches apart on center. I prepared the second strip (or "rail") the same way. One rail I placed on the floor along the wall where I wanted the Fluorescent Light Organ, about 4 inches out. Then the 38 (that is all I could fit on one 8 foot rail) tubes were set into the holes in the bottom rail, leaning against the wall. A strip of painter's tape was then run across all the tubes to keep them upright. The top rail, being slightly flexible was then attached across the tubes top end pins, working from one end, one at a time. The top rail was then screwed to 4 studs in the wall with insulating brackets The bottom rail was then pushed by degrees back against the baseboard. This put the glass part of the tubes just over one inch apart. This measurement is purely arbitrary and it works well for me. However, experimentation with this spacing could perhaps result in an even better operation.

I became concerned that since the coupling capacitor carrying the high-voltage audio to the top rail of the array might short-circuit. This would result in a very high DC voltage from the plate of the output tube in the amplifier being continuously present on the top ends of the tubes along with the audio driving signal, without warning! After some experimentation I discovered that a step-up transformer could be utilized to provide the drive audio from the low-voltage loudspeaker terminals of the amplifier instead of getting it from the plate circuit directly. The first step-up transformer I tried came from a neon sign, capable of producing 30 Kilovolts or so from a 110 Vac input. Since the amplifier I now use has a 110 Volt output as well as 4,6,and 8 ohm loudspeaker outputs, the rig worked pretty well. I soon noticed a reduced lighting effect of the organ at the higher audio frequencies. I theorized this could be due to some built-in filtering to curb RF interference in the neon transformer, and started looking for a step-up transformer with better high-frequency response. When I finally connected an old cylindrical Ford auto spark coil primary connector to the 4 ohm loudspeaker output of my amplifier and connected its high-voltage end to the top and bottom rails of the Light Organ and turned on the music-Eureka! The final modification came after a few of the tubes seemed to hog the show, being lit brighter and longer than the others. Disconnecting the ground wire from the bottom rail from the spark coil ground (amplifier ground) mostly cured this. This means that the bottom rail connection to the amplifier is only through the carpet and the concrete floor beneath. This gives a much more interesting and beautiful performance, just a bit dimmer. The audio drive current to the tubes is very small, being fed through a wire too thin for most people to see in normal room lighting, so it seems there is no source for the lighting energy. After folks' eyes become accustomed to the dark, though, turning up the volume will light all the 38 lights brightly enough!

I have always used a tube amplifier to drive the Fluorescent Light Organ because I have read that tube amplifiers are not damaged by a short-circuit on their output, whereas a transistor output stage might be. The amplifier I use currently and for the last 30 or so years is a Bogen industrial amp with 4 output tubes in push-pull parallel, rated at 100 watts out. An amp with less power would probably work also. I get my signal from the left Wharfdale speaker in my stereo setup with no tone-shaping. I would never use an automatic level control because with my hand on the volume control of my stereo, I am the MAESTRO!!!

Doug Booth, Jr. C.P.B.E. Light Organ Developer


Thank you for sharing this information, Doug!

Here is a diagram of the original FLO schematic using a vacuum tube power amplifier as described in his article. I consider this circuit to be very dangerous and strongly do not recommend using this method.

Next is a diagram using an automobile type ignition coil. As Doug states above, other high voltage type transformers can be used instead of the ignition coil. I consider this circuit to be much safer than the previous one, although still hazardous, and suggest this method as the one to use if you are building your own FLO.

Here is a picture of Doug's large FLO installation. Now that looks impressive!

Here are a couple of pictures showing the details of the mounting and wiring:

Based on Doug's information I built a prototype FLO to see how easily it could be done. Since I had a bunch of 15 inch fluorescent tubes on hand they were an obvious choice for the project. For the high voltage I used a salvaged laser power supply transformer with a 100 watt power amplifier driving the primary and the high voltage secondary connected to the tubes. Since these tubes were relatively small I hoped that the lower voltages would still be sufficient to work. Here is a picture of the assembled prototype:

When first tested only some of the tubes would light up, and once one had been lit for a while it tended to draw most of the current preventing the other tubes from lighting. As well, I had to run the power amplifier fairly hard to get things working. Apparently the voltages needed to be a bit higher to make this prototype work well. As well, these particular tubes were a mix of different types, with some almost new and some well used, so that might have contributed to the problems.

In order to get higher voltages, I inserted a standard 120V primary 25V secondary power transformer into the circuit, with the secondary connected to the amplifier and the primary connected to the laser transformer. In theory the new transformer should boost the high voltage almost five times higher than before. This modification allowed the amplifier to run at a more comfortable level, but did nothing to change the problem with only some of the tubes working.

I then experimented with adding resistors in series with each tube, and found that 22k resistors allowed all of the tubes to function. Below is a picture of the resistors temporarily in place.

The lamps were not quite as bright as before, but now the FLO appeared to be functioning satisfactorily. Here is a video a video of it in action:

Although I'm sure that Doug's big FLO is much more spectacular and interesting to watch than this small one, for the zero cost and small amount of effort that this project required the result is quite amazing!