The ADELINE project aims to develop a new generation of very low energy lamps where the fluorescent discharge between cathode and anode is no more initiated and sustained, as in the present lamps, by a very energy costly thermo-emissive hot cathode (cathode heating, extraction and acceleration of electrons for producing the cathode plasma), but by about 1 cm surface-wave plasma produced at the cathode with a microwave electric field, at a power below one watt. The expected gain in electric power is higher than a factor of 2. The absence of hot cathode also allows for the substitution of mercury by sulfur, very reactive at high temperature, but whose UV spectrum (280 - 400 nm), close to the visible domain (in contrast to the resonant peak line of mercury at 253.7 nm) provides an additional gain of factor 1.4 on the conversion of UV photons into visible photons by using optimised phosphors. So, by direct comparison with commercially available mercury tubes of 100 lm/W, one may, from now, anticipate light efficiencies of the order of 100 × 2 × 1.4 = 280 lm/W.
Furthermore, with the direct control of the cathode plasma density (and consequently of the discharge current) by microwaves, ballast become useless, hence significant gains in terms of electric power reduction (of the order of 17% at equal discharge powers) and cost reduction. At last, by initiating the plasma with microwaves, instantaneous lighting of the discharge lamp can be obtained, as also the modulation of the discharge current by using a dimmer or by remote control of connected lamps.
A second challenge of the ADELINE project is the study of N2/O2 gas mixtures at low oxygen content (< 1%) as a potential alternative to sulfur (of low volatility at cold temperature) for the production of UV photons close to the visible range. When, in the case of sulfur, UV photons come from the molecular spectrum of S2, it is, in the case of N2/O2 gas mixtures, the formation of NO molecules in the excited states NO(A) and NO(B) which is responsible for the important emission of UV photons, in particular in the 200 – 275 nm domain for the NO_gama system and in the 280 – 400 nm domain for the NO_beta system. It is this last spectral domain, contiguous to the visible domain, that should be promoted (by adjustment of discharge operating conditions) in order to obtain a maximum efficiency in the conversion of UV photons into visible photons with optimised phosphors.
The last challenge of the ADELINE project deals with the choice of phosphors. The conversion of UV photons into white light requires to associate at least 3 phosphors emitting in the red (R), the green (G) and in the blue (B), thus constituting a RGB system such as the sum of their emission spectra covers the whole visible domain. The choice of inorganic phosphors exhibiting high stability under thermal or photonic stress and especially chemical stress (with regard to sulfur and oxygen) forces itself. The excitation domain of phosphors must also fit in with the UV spectrum of S2 or N2/O2 emitters and their quantum conversion efficiency be close to unity.
The program includes the design and production of a series of models and prototypes with different parameters (e.g., phosphors or formulations of RGB systems) at the successive stages of the project progress, from pre-models of hybrid discharges up to lamp prototypes in order to determine their colorimetric characteristics (rendering colour index RCI and correlated colour temperature CCT index) and to measure their nominal values, electric power in W and light flux (or light efficiency) in lm (or lm/W).
The valorisation strategy mainly focuses on tertiary and domestic lighting sectors with the fluorescent tubes and the fluorescent compact lamps where the absence of ballast and hot cathode strongly facilitates miniaturisation.
Madame Ana Lacoste (Laboratoire de Physique Subatomique et de Cosmologie)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
Pprime Institut P' : Recherche et Ingénierie en Matériaux, Mécanique et Energétique
LPSC Laboratoire de Physique Subatomique et de Cosmologie
ICCF INSTITUT DE CHIMIE DE CLERMONT-FERRAND
Help of the ANR 408,312 euros
Beginning and duration of the scientific project: December 2020 - 42 Months