Method of making a plasma lamp
View Patent ↗An apparatus and method for achieving desired spectral emission characteristics in plasma lamps is disclosed. The apparatus and method use multi-layer thin film optical interference coatings to selectively reflect a portion of the light such that it can be absorbed in the plasma. The multi-layer thin film coating is applied to any surface of the lamp, which substantially surrounds the plasma. The number and thickness of the layers in the coating are selected to ensure that significant portion of the selected light emitted from the plasma is reflected by the coating and absorbed by the plasma. The properties of the coating, reflectance, transmittance and absorption are determined as a function of plasma and lamp characteristics. These characteristics include the spectral emission characteristics of the plasma, the spectral absorption characteristics of the plasma, the physical dimensions of the plasma, the angular distribution of the light emitted from the plasma on the coating and the geometry of the coated surface.
1. A method of making a high intensity discharge lamp having a vaporizable fill material of one or more metal halides forming a light emitting plasma during operation of the lamp, said method comprising the steps of:
selecting a fill material comprising halides of sodium, scandium and thorium; and
filtering the light emitted from the plasma,
so that the operating characteristics of said lamp include a lumens per watt greater than about 85, a color rendering index greater than about 80, and a correlated color temperature between about 3000° K. and about 6000° K.
2. The method of claim 1 wherein the step of filtering the light comprises providing a notch filter which reflects at least seventy percent of the light generated by the lamp within a narrow wavelength band in the visible spectrum and transmits at least seventy percent of the light generated by the lamp within the visible spectrum and outside of said narrow band.
3. The method of claim 2 wherein the notch filter reflects at least eighty percent of the light generated by the lamp within a narrow wavelength band in the visible spectrum and transmits at least eighty percent of the light generated by the lamp within the visible spectrum and outside of said narrow band.
4. The method of claim 2 wherein the narrow wavelength band is substantially centered on a wavelength of about 590 nm.
5. A method of making a lamp comprising the steps of:
(a) providing an arc tube containing a light emitting plasma;
(b) determining the spectral emission characteristics of the plasma;
(c) identifying wavelengths of light undesirable for transmission from the lamp;
(d) determining the spectral absorption characteristics of the plasma;
(e) identifying respective regions within the plasma efficient in absorbing light at each of the identified wavelengths; and
(f) providing a filter on the arc tube that substantially reflects the plasma-emitted light at the identified wavelengths back towards the identified respective regions.
6. The method of claim 5 wherein the step of providing a filter comprises the steps of determining the number and thickness of the layers in a multilayer coating and applying the coating to a surface of the arc tube.
7. A method of making a plasma lamp comprising:
(a) determining the spectral emission from the plasma;
(b) determining the location in the plasma of one or more arcs emitting light at one or more wavelengths of interest;
(c) determining the angle of incidence to the arc tube of the light emitted at one or more of the wavelengths of interest;
(d) determining the number and thickness of the layers of a multilayer coating for application to the arc tube so that at least a portion of the light emitted from the plasma at the one or more of the wavelengths of interest is reflected by the coating toward the arc emitting the light at the wavelength of interest; and
(e) applying the multilayer coating to the arc tube.
8. The method of claim 7 wherein the CRI of the light transmitted by the coating is greater than about 80.