Electric lamp and discharge devices – With gas or vapor – Having a particular total or partial pressure
Reexamination Certificate
1999-09-15
2003-10-21
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having a particular total or partial pressure
C313S483000, C313S564000, C313S571000, C315S112000, C315S117000, C315S291000, C315S307000
Reexamination Certificate
active
06635991
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of adjusting a desired spectrum of the light emitted by a gas discharge lamp during its operation, wherein the gas discharge lamp comprises a discharge chamber closed in a gastight manner with a first ionizable substance and a second substance less readily ionizable than said first substance both present in the discharge chamber, at least a portion of the first and of the second substance being in the gas state during operation, and which gas discharge lamp is operated under mm voltage and current conditions such that at least the gas of the first substance can be ionized and the second substance can be excited.
It is known to adjust the spectrum of the light emitted by a finished gas discharge lamp during its operation. The lamp is operated for this purpose by means of very short pulses of high power. The pulsatory character (with pulse durations of the order of 1 microsecond) makes the electron temperature very high, so that the less readily ionizable gaseous substance, for example neon, is excited and starts contributing to the spectrum.
Such a method has the disadvantage that a comparatively expensive electronic circuit is required for generating the high-power pulses of very short duration.
SUMMARY OF THE INVENTION
According to the invention the ratio of i) the partial pressure of the first substance to ii) the partial pressure of the second substance is adjusted in dependence on the desired spectrum.
It was found that the modification of the ratio of the partial pressures renders it possible to adjust the spectrum. The ratio between i) the intensity integrated over a wavelength range which is a fraction of the wavelength range of the full desired spectrum and ii) the intensity integrated over the wavelength range of the entire desired spectrum is changed thereby. Both the first substance and the second substance contribute to the spectrum by the emission of light. It has long been generally known that an energy-saving lamp positioned outside in winter shows a color deviation at least during starting as a result of the temperature conditions and accompanying lower partial mercury pressure, but no proposals for adjusting the spectrum of the light of a gas discharge lamp as desired are as yet known to Applicant which involve the modification of the partial pressure of a gas present in the gas discharge lamp. It depends on the application what a desired spectrum will be. The wavelength range of the desired spectrum will correspond to the wavelength range which plays a part in light-dependent physiological processes in the case of lamps used in greenhouses. The use of lamps for illuminating a human domestic or professional ambience requires a wavelength range to which the human eye is sensitive. It is noted here that, if luminescent substances are used, it will be clear to those skilled in the art that a desired wavelength range as mentioned above is derived from a desired wavelength range with which the luminescent substances can be suitably excited. The following definitions are used in the present application. The term ‘reference pressure’ is understood to mean the partial pressure which prevails in a non-operating gas discharge lamp when this lamp has a temperature equal to the temperature of the portion of the lamp which defines the pressure of the first substance.in the situation in which the lamp is on (this is usually the coldest spot in the discharge space of the lamp) while the lamp is operated at an ambient temperature of 25° C. Under these conditions, that portion of the first substance which is in the gas state is distributed at least substantially homogeneously in the cavity of the lamp's discharge chamber. The reference pressure serves as a measure for indicating how much of a certain substance should be present in the gas state for a functional gas discharge lamp. As will be explained further below, the concentration of the first substance may differ locally during operation of the gas discharge lamp. In that case, the term ‘local partial pressure’ will be used for the relevant location. The essence of the present invention is that the local partial pressures are adjusted in that portion of the discharge lamp where the discharge takes place, i.e. in the discharge space. Where the ‘partial pressure’ is referred to without further particulars herein, the local partial pressure such as prevails in the center of the discharge space is meant, the center being that portion of the discharge space which lies farthest away from the wall. The first substance and the second substance differ from one another by their different emission spectra. Small differences may be sufficient in the case of luminescent materials, such as phosphors, provided luminescent materials are used which have different sensitivities to the two mutually resembling emission spectra. Usually, the pressure of the gas mixture in the lamp will be between 10 and 10,000 Pa. The second, less readily ionizable substance will usually be present in excess quantity compared with the first substance. The ambient temperature will generally be at least 15° C.
Advantageously, the ratio of the partial pressures is modified such that the ratio of i) the intensity integrated over a wavelength range which is a fraction of the wavelength range covering the full desired spectrum to ii) the intensity integrated over the wavelength range of the full desired spectrum is changed by at least 3% with respect to a preset value.
The modification by at least 3% renders possible a change which is subjectively observable for a user. The emission spectrum is defined as the emission spectrum as it can be measured at the inside wall of a gas discharge lamp.
In a major embodiment, a gas discharge lamp provided with a luminescent material is utilized, and one of the substances in the gas state emits visible light having a first spectrum while another substance in the gas state emits UV radiation, which UV radiation excites the luminescent material so as to emit visible light having a second spectrum different from the first spectrum.
The emission of visible light renders it possible to achieve a modified spectrum without a further luminescent material being necessary for this in addition to the luminescent material necessary for converting UV radiation into visible light.
Advantageously, a rare gas is used as the second substance, in particular neon or xenon. Mercury is suitable for use as the first substance.
Such substances are highly suitable for operating the gas discharge lamp according to the invention. In particular, neon renders it possible to change the proportion of red light through direct emission. Xenon is interesting because of its UV emission spectrum which is different from that of mercury, so that it can be used in combination with mercury. Mercury is interesting as the first substance because its partial pressure can be adjusted by means of a gas/liquid or gas/solid phase transition.
Advantageously, therefore, in order to modify the partial mercury pressure, the gas discharge lamp is provided with liquid mercury or an amalgam, the temperature of which is adjusted for adjusting the ratio of i) the partial mercury pressure to ii) the partial pressure of the second substance.
The reference pressure of mercury can thus be modified in a simple and inexpensive manner (by means of a gas/liquid or, in the case of an amalgam, a gas/solid phase transition), and accordingly also the local partial mercury pressure and the spectrum of the light of the gas discharge lamp.
In an interesting embodiment, the temperature of the gastight sealing wall of the discharge chamber is adjusted by electric cooling and/or heating means which are in heat-conducting contact with the wall.
The cooling and/or heating means may be suitably chosen from i) a current resistor provided on at least a portion of the wall of the gas discharge chamber and ii) a Peltier element. The current resistor may be, for example, a current-conducting coating, such as a tin oxide coating, provided on
Bakker Levinus P.
Kroesen Gerardus M. W.
Patel Ashok
Roy Sikha
U.S. Philips Corporation
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