In old glow sets, which dominated the market a dozen or so years ago, the characteristic red bulb plays a special role. It is the heart of the entire system – a simple interrupter that gives rhythm to the Christmas twinkle. The mechanism is based on the phenomenon of thermal expansion of metals. The bimetallic strip, placed inside the bulb, reacts to the flow of current, heats up and bends, temporarily disconnecting the circuit.. After cooling down, it returns to its place and the cycle starts again. As a result, the entire chain of lights pulsates at an even rhythm – without additional drivers or electronic systems.
This solution was inspired by classic thermal interrupters, used in traffic lights and simple electrical systems already in the mid-20th century.
The red color of the bulb was a deliberate attempt by the producers – allows you to easily distinguish the functional element from other bulbs. Replacing this lamp with a regular one results in the loss of the flickering effect, so the entire chain lights up continuously. In the 1990s and 2000s, many users, unaware of its role, tried to replace it with another bulb, which unfortunately led to frustration and the mistaken belief that the set was defective.
From an engineering point of view, the system based on a bimetallic bulb was almost an ideal of simplicity. It did not require additional electronic systems, and its operation was based solely on the physics of materials. The bimetallic strip, reacting to temperature changes, acted as a natural switch. Thanks to this, the lamp sets were cheap to produce, resistant to failures and available to mass consumers. In Central Europe, where the lighting market developed dynamically in the 1980s and 1990s, such solutions have become standard in homes, offices and public spaces.
However, as time passed, limitations appeared. The incandescent light bulbs were heating up to high temperatures, and this unfortunately increased the risk of burnout and increased energy consumption. In the 2000s, more attention began to be paid to issues of safety and energy efficiency.
European standards, i.e. the ErP directive of 2009, gradually eliminated traditional light bulbs from the market, opening the way for LED technology. Although the bimetallic interrupter was a brilliant solution in its simplicity, it could not meet the new requirements – both in terms of energy savings and durability. Today it remains a fascinating example of how clever physics has been able to shape everyday technology for decades.
LEDs consume even several times less electricity than classic light bulbs, and at the same time they almost do not heat upand. This is of real importance in homes where the lights stay on for hours, often near dry Christmas tree branches, curtains or paper decorations. Lower energy consumption also means lower bills and less load on the home electrical installation.
Their durability is equally important. Modern LED lamps can operate for many seasons without replacing individual elements, they are shock resistant and less susceptible to failure of the entire chain. Additionally, manufacturers today offer a wide selection of colors, light temperatures and effects, controlled by remote control or application, which a few years ago was reserved only for expensive decorative installations. LEDs simply fit better into the pace of modern life: they are convenient, predictable and hassle-free.
