VEB Leuchtenbau Wittenberg v2.0
This fluorescent light was produced in 1989 in East Germany by VEB Leuchtenbau Wittenberg. It has an air-tight design with one centimetre thick borosilicate glass which makes it suitable to use in explosion-sensitive areas. These lights where often used in places like laboratories and chemical plants. This model is comparatively rare because of its small size that only uses two 18w fluorescent bulbs.
The state owned company was perhaps better known as Paul Mrosek KG, its namesake being a pioneer in the field of industrial fluorescent lighting. His products are highly utilitarian, but they are beautifully designed as well. We found “Typ 86.11.1” at a place that imports industrial vintage and fell in love with it. Since it has a prominent place in our living room and is an important part of our lighting plan the electronics needed an upgrade to comply with the demands of its new environment.
The original electronics consist of two cold white Narva T12 fluorescent tubes (also from ’89), a magnetic ballast, two neon starters and a MKP capacitor. The solid core wiring was loosely routed through the enclosure; economic and practical for use in a factory, not to aesthetically pleasing when applied in a living room.
v1.0 Modernizing core functionality
In stage one of this project, the lamp upgrades to an electronic ballast, gets outfitted with new wiring and it is refurbished. In terms of refurbishment, it is thoroughly cleansed, freshly greased and the internal framework is resprayed. Special care was taken to conserve the original details. The cold white tubes are replaced by (new old stock) warm-white tubes by Narva! This redesign is about improving upon a great product, while respecting its legacy.
Working principle of a hot-cathode FL
The lamp consists of a glass tube filled with an inert gas like Argon and a tiny amount of Mercury. On each side of the tube a tungsten electrode can be found that emits electrons into the tube by thermionic emission. The electrons ionize the inert gas and create an arc. The heat of the arc vaporizes the Mercury and its atoms start to collide with the fast moving electrons in the tube. These collisions excite the atoms onto a higher level of energy. When the atoms return to their stable energy state, they give off the difference in energy in the form of photons at the frequency of UV-light. These photons hit a coating of phosphors on the glass tube and are converted into visible light.
Original electronics (magnetic ballast + starter)
Alternating current (50Hz) is passed through a ballast, which steps up the voltage (420V in case of the original Weltor in this lamp) and limits the current flow through the electrodes by inductance. A fluorescent lamp has the properties of negative resistance; an increase in current through the fluorescent tube causes a drop in voltage across it. Without a ballast the dropping voltage would result in an ever increasing current flow, until the lamp destroys itself.
To get the arc started a high voltage is needed; that is where the glow tube starter in the original configuration of this lamp comes into play. The starter contains a bi metallic switch which is normally open. When power is applied a (neon) glow discharge takes place which causes the switch to heat up and close, ending the glow. This supplies current to the electrodes in the main lamp and starts the -local- thermionic emission. After about 1 to 2 seconds the bimetallic contacts cool and open the circuit again. The magnetic field in the ballast collapses and sends an inductive kick through the lamp that starts the arc. This process repeats itself until the arc is realised, hence the flickering of older lamps.
Improved electronics (digital ballast)
The lamp is retrofitted with a digital ballast from BAG electronics (BCD57.1) that is mounted on a custom bracket that fits in the original position of the ballast. By using this type of control gear, the fluorescent tube can be maintained -as opposed to switching to led- while yielding significant advantages over the original components:
- Flicker free operation by driving the lamp at 50-125 KHz
- 1-10V Dimming interface, dimmable between 3-100%
- Smart electronics that monitor lamp operation and control the start.
- More power efficient
The new electronics not only improve the performance of the lamp, it offers way more control. Stage 2.0 of this project takes advantage of those features.
v2.0 Preparing for the future
Currently in progress…