A light organ is an electronic

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

 device which automatically converts an audio signal such as music into rhythm

Rhythm

Rhythm may be generally defined as a "movement marked by the regulated succession of strong and weak elements, or of opposite or different conditions." This general meaning of regular recurrence or pattern in time may be applied to a wide variety of cyclical natural phenomena having a periodicity or...

ic light effects. In the 1970s, light organs were a popular lighting effect used in discotheques and dance parties

Party

A party is a gathering of people who have been invited by a host for the purposes of socializing, conversation, or recreation. A party will typically feature food and beverages, and often music and dancing as well....

. The multicolored lights of the light organ would pulsate to the beat of the music.

Technology

The circuit

Electronic circuit

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...

 of a light organ separates the audio signal into frequency

Frequency

Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...

 bands and controls the light channels according to the average level of each band using dimmer

Dimmer

Dimmers are devices used to vary the brightness of a light. By decreasing or increasing the RMS voltage and, hence, the mean power to the lamp, it is possible to vary the intensity of the light output...

s. A typical party light organ of the 1970s had three spotlights, red, green and blue, for sounds in bass

Bass note

In music theory, the bass note of a chord or sonority is the lowest note played or notated. If there are multiple voices it is the note played or notated in the lowest voice. While the bass note is often the root or fundamental of the chord, it does not have to be, and sometimes one of the other...

, medium frequency and high frequency.

Due to their simple structure, light organs were popular as DIY projects for electronics hobbyists in the 1970s and can still be found for sale on the internet

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

.

In 1971, the Rickenbacker

Rickenbacker

Rickenbacker International Corporation, also known as Rickenbacker, is an electric and bass guitar manufacturer based in Santa Ana, California...

 guitar company offered their 331LS "Lightshow" model (and matching bass, model 4005LS), the body of which contained a three-channel light organ (with a dimmer); each channel corresponded to the pitch of the strings being played. The soundboard on these models was replaced with thin plexiglass cutouts over a translucent moire diffraction

Diffraction

Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...

 material.

With the widespread adoption of cheap PC

Personal computer

A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...

s, some hobbyists started experimenting with using PCs for frequency analysis instead of analog filters.