is a small device used with cheap pocket cameras, first introduced in the 1960s, to serve as a disposable illumination
source. Rather than using expensive reusable flash lamp
s, 'pocket' cameras up until that point used flashbulb
s - small disposable glass bulbs which contained a quantity of a pyrotechnic
substance. When the shutter was tripped, the camera would ignite the substance in the bulb, producing a flash of bright light which would provide illumination for the shot. Although of uneven quality and only useful for one shot, flashbulbs nevertheless brought the ability to shoot in low light to the hobbyist photographer, just as low-cost cameras had brought photography itself within range of the budget enthusiast.
The main problem with flashbulbs, however, was that they needed to be replaced after each shot. In addition, they were always hot after discharge, and if they were handled too soon, they could crumble - resulting in bits of plastic and/or glass (depending on construction) all over the place. This caused a sometimes-frustrating delay for the photographer, who might be attempting to take multiple photos while their subjects posed, for example.
Kodak introduced several new cameras in its Instamatic line in the late 1960s. One of these used the 126 film cartridge (which had been around since the line's start in 1963) and had a socket on the top. This socket was for the new flashcube that Kodak was marketing along with the proprietary cartridge film.1
The flashcube was designed to complement this. It contained four roughly standard flashbulbs, filled with the same pyrotechnic, but they were set inside a clear-walled plastic cube perhaps twice the dimensions of standard gaming dice. Each bulb was set along one edge, and there were reflective panels of plastic set from each corner in to the center, making a rough parabolic reflector around each bulb to better utilize the light and protect the cameraman from the glare.
At each shot, the camera would trigger the currently forward-facing bulb using electricity (provided by a battery) through the socket. When the camera was wound for the next picture, the flashcube would rotate ninety degrees, presenting a fresh bulb for use. In this manner, four shots could be taken in rapid succession; reloading was a much quicker operation, since the cube itself was not weakened by the bulbs' detonations, and socketing the cube's base was not nearly as delicate an operation as handling the fragile fresh bulbs themselves. As an added bonus, the whole assembly could be more simply packaged for retail sale, as the sturdy plastic cube itself provided a great deal of both durability and padding, and (best of all!) could be priced higher for the convenience. Kodak, which was manufacturing and selling the pocket cameras on the 'razor and blades' model, rubbed its hands at yet another means of lining its pockets.
Of course, the Flashcube (tm) was quickly copied, as GE and Sylvania produced licensed Flashcubes and then their own Magicube, with a different mounting system and a physical trigger using piezoelectrics to avoid the requirement for a camera battery. Once the genie was out of the bottle, all manner of packaging schemes arose. Another popular method was the flip-flash, a vertical bar containing ten bulbs set into a flat plastic package which stuck up from the camera and socketed into an electrical connection. These were fired as squibs, powered by a battery in the camera, using a set of traces in the socket and a simple fusing path which advanced the live trace as each bulb was used. After five shots, the user would 'flip' the bar to mount at the other end, using a mirrored set of traces - hence the name. Another variant of this was the flashbar, which had all ten bulbs in a line and was mounted horizontally atop the camera. This was popular with Polaroid, whose cameras did not have top-mounted shutter buttons and did not need the top space.
The Flashcube was used for many purposes, though. Children, ever the eager discoverers, swiftly realized that what would go pop for a camera would also go pop if thrown hard against a rock - and the Flashcube, being marketed as 'safer' since it was so carefully cocooned in plastic, was easier to get a hold of (especially if you were holding a camera and had an innocent face). These could then be used for all manner of entertainment, either on their own (throwing them against rocks didn't work nearly as well as individual bulbs, and trying to extract the bulbs nearly always broke them, but oh, the fun to be had with Learn-Your-Electricity! kits...) or with assistance. For example, toy grenades that used Flashcubes for effects (United States Patent 4461117).
Once xenon flashlamps and capacitors got cheap enough that even disposable cameras could pack decent flash systems, an entire industry went poof (ha!) practically in the night (double ha!). Still, many of my summer camp memories are brought back to me by the sight of snarled grey fibers behind glass, or the smell of hot burning plastic.
1 Thanks to DonJaime for patiently correcting my obstinate incorrectness regarding the history of Kodak Instamatics. :-)