Light without shadow
The e³ lamps belong in the category of low-pressure discharge lamps. They consist of thin glass tubes with a diameter of about 3mm. The tubes can be processed mechanically, which allows for flexible adjustment of their shape. Most specimens are coated on the inside with doped ceramic materials and also contain a so-called getter, that is, a chemically reactive material that helps to keep the vacuum clean for as long as possible. In addition, there is a special mixture of inert gases present at a pressure between roughly 2mbar and 0.7bar.
The lamps contain high capacity corrective phosphors which can also contain individual dopants that generate red, green and/or blue emission. The latter are used to produce and refine the desired light spectrum (light color). The standard operating voltage for e³ light sources is 24 V.
Functional principle
The complex principle on which e³ (energy efficient excitation) technology works is based on the ionisation of vaporous or gaseous particles. Careful process control enables production of short-lived clusters (exciplexes) emitting ultraviolet, visible and/or infrared light. Selective combination of these emissions can be used to obtain the desired light spectrum.
The plasma processes also produce a small amount of light at extremely long wavelengths, and this can be used to control and regulate the processes according to a patented method. Applying voltage produces an electrical field which accelerates electrons and elementary particles (ions, atoms, molecules) inside the glass tube, causing them to collide. The electrons emitted from these collisions are refined in the ceramic layer by adding, filtering and/or converting high energy photons (3 to 6 eV) into low energy photons. Photons then exit the glass tube with the desired light spectrum.
Inert gases are used as buffers in the tubes because they make it relatively easy to arrive at a stable ionisation. Depending on the set of components, different types of clusters, and hence different emissions from elementary particles, can be produced.
Optimising the lighting process
Undesired material removal from electrodes, also known as sputtering, strongly reduces the life span of traditional fluorescent lamps such as CCFLs or energy-saving lamps. High voltages, low temperatures, and uncontrolled regulation are only some of the processes that can cause accelerated ageing and premature failure. The material removal also modifies the gas atmosphere inside the glass tube through chemical processes, which further accelerates the ageing process.
It had been long thought that electrode sputtering was an unavoidable hazard, but e³ light sources (Figure 1) illustrate that this conclusion is incorrect. Thanks to control of the complex physical processes present during discharge, intelligent activation and the use of special materials in manufacturing, e³ lamps are virtually free of sputtering problems and their effects. This increases the performance as well as the life span of the products.
Figure1: Due to their small diameter, e³ tubes can be produced in a wide variety of forms
Typically, light sources of similar size, such as CCFLs, are usually close to conductive materials, for example reflectors, screens or shells. These create parasitic capacitances between the light source proper and its surroundings, which in turn causes leakage currents. These leakage currents cause a decrease in amperage from the hottest to the coldest point of the light source. As the light intensity depends on the amperage inside the lamp, this leads to the undesired effect of the lamp appearing significantly brighter on its hot than on its cold side.
e³ light sources offer a remedy for leakage currents and parasitic capacitances – without reductions in operating frequency (typical operating frequencies of e³ lamps being 100 to 250kHz) or lamp voltage. The key lies, among other aspects, in the significant reduction and meticulous control of the operating impedance. Operating impedance is 4 to 6 decades less than the lowest amount possible in fluorescent lamps, CCFLs or other related fluorescence technologies today.
The behaviour with temperature of light sources is another important point. As most fluorescent lamps used today are based on mercury-arc excitation, many of their characteristics directly depend on the achievable amount of vapor pressure, which is in turn heavily influenced by temperature. Over time, several technologies have been aimed at reducing this dependency, all with varying degrees of success. For example, while less gas pressure inside the lamp reduces reabsorption of the light generated, it also encourages electrode sputtering. For this reason, modern energy-saving lamps use amalgams, although this is not a totally satisfactory solution either, as the lamps consequently have a very long warm-up time and their life span becomes shortened by frequent on/off cycles.
Issues with operating temperature are obviated with e³ technology as the light generating process avoids any dependency on a single variable such as mercury vapor pressure. A dynamic equilibrium within the allowable parameter space is generally the case, and this equilibrium can be shifted in different directions and to varying extents, thus enabling dynamic process control and intelligent activation during operation. This makes it possible to superimpose the respective achievable equilibria of several different elementary processes in a way that ensures the desired temperature independency over a very wide temperature range, even way below 0°C.
Measuring efficiency
Global Lightz determine the efficiency of their light sources (without shells, reflectors and light guides) through measurements with an integrating sphere at an ambient temperature of 25°C (Figure 2). Data measured include the amount of electrical power (watt) that is effectively used, as well as the quantity of light emitted (lumen). These data are integrated over the visible light spectrum and averaged over a short succession of measurements (three to five). All efficiency measurements are taken at the full load specified for each test item. This is a significant departure from testing standards for LEDs, which is typically carried out during filtering and grouping (binning) of individual color values, measured at very low amperages (often 10mA) and with very short pulses (often a pulse of 10ms) at a temperature of 20°C.
Figure 2: A staff member of Global Lightz measures an e³ light source
Total cost of ownership
In order to analyse the total cost of ownership of light sources, the manufacturer calculates each cost factor for the maximum life span of the product and adds them up. The calculation also needs to account for the number of make-and-break cycles for which the product is designed and the question of its recyclability. The calculated life span of e³ products is based on the mean time to half brightness – the period of time it takes for the lamp to lose half of its initial brightness.
Standard products are specified for an average life span of 75000 hours at 25°C. These numbers are based on field data from 15 years of product use in more than 70 countries with the most diverse climatic conditions. Furthermore, the products reliably meet special requirements in terms of shocks, vibration, humidity or extreme temperature.
Examples of use
Due to their ruggedness and temperature independency, e³ light sources are, among other things, suitable for outdoor applications such as street lighting. A further characteristic that makes e³ fundamentally different from CCFLs and LEDs is the fact that e³ light sources produce shadowless light. Global Lightz is currently developing an e³ lighting solution for a leading manufacturer of commercial refrigerators. Compared to LEDs, it allows a more appealing display of goods, especially since e³ technology has a clear advantage over LEDs when it comes to simulating daylight and dynamic light: while LEDs approximate the daylight spectrum from the edges of the RGB color space, e³ light sources directly access the daylight values of the Planckian curve.
Apart from commercial applications, this artificial daylight, free from shadows and distortion, also offers interesting possibilities for laboratories and similar environments. At the Light+Building 2010 fair in Frankfurt, Global Lightz presented an e³ lamp with a continuously variable color temperature between 2000 and 20000K, thus simulating daylight just as easily as candlelight or the light of incandescent bulbs (Figure 3).
Figure 4: Light for interior design: the latest e³ light source can simulate both incident daylight and the light of candles or bulb.
Summary
e³ light sources can produce up to twelve times the brightness of an incandescent lamp at only ten per cent of its power consumption. Their long life span of more than ten years and resistance to extreme ambient temperatures from -35 to +250°C enable a very wide range of applications. In contrast to all other light sources, e³ lamps are capable of producing practically shadowless light in very close proximity to the natural daylight spectrum.
About the Author:
Dipl.-Ing. (FH) Ruediger Simon is Managing Director and head of operations of Global Lightz. He gained many years of experience with strategic projects in the areas of industrial lamps and light sources from previous employment in the international light market.
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