WO2010133987A1

WO2010133987A1 - Design spaces for high wattage ceramic gas discharge metal halide lamp to minimize arc bending

Info

Publication number: WO2010133987A1
Application number: PCT/IB2010/051886
Authority: WO
Inventors: Ray Gibson
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2009-05-18
Filing date: 2010-04-29
Publication date: 2010-11-25
Also published as: TW201123259A

Abstract

A high wattage (HW) ceramic gas discharge metal halide (CDM) lamp (10) has a shaped discharge vessel (12) with an amount of mercury (Hg) and a distance (ED) between the discharge electrodes (13a, 13b) designed to result in high voltage operation with minimal bending (d) of the discharge arc, making such lamps candidates for replacement of quartz metal halide (QMH) lamps in high voltage ballasts. Applications include high wattage applications such as very high bay, warehouse, roadway, parking lot and sports lighting.

Description

Design spaces for high wattage ceramic gas discharge metal halide lamp to minimize arc bending

BACKGROUND OF THE INVENTION

This invention relates to ceramic gas discharge metal halide (CDM) lamps, and more particularly relates to a design space for such lamps enabling operation at high wattage with minimal arc bending.

Currently the lighting market for white light is dominated by quartz metal halide (QMH) lamps which have been available in wattage ranges from 35W to 2000W. These lamps are typically used in shop and retail lighting (low wattage), high bay commercial and industrial lighting (medium wattage), and very high bay, warehouse, roadway, parking lot, and sports lighting (high wattage) applications.

High wattage (HW) QMH lamps (750W and above) have high luminous efficacies, up to 120 LmAV, and a range of color temperatures from 3000 K to 5600 K with 4000 K being the most used in the North American market. These lamps operate at high voltages compared to the lower wattage lamps, the 750W and IOOOW QMH lamps for example having nominal voltages of 200 volts and 265 volts, respectively.

These high voltages, which are achieved through long arc lengths and high mercury (Hg) dose weights, are employed to keep lamp currents to levels that minimize electrode heating losses, and to keep magnetic ballast losses low. However, these design features can lead to arc bending, arc helical instabilities, and color de-mixing, leading to lifetimes of less than 16,000 hours, marginal color rendering (color rendering index (CRI) values of about 65), and poor lumen maintenance over life caused by blackening and sodium loss.

CDM lamps employ a ceramic discharge vessel of polycrystalline alumina (PCA) surrounded by an outer glass envelope and a base sealed to the envelope to provide a gas- tight enclosure. The discharge vessel has a certain shape to accommodate high internal pressure and provide minimal thermal gradients. The discharge vessel typically contains a fill of an inert gas, a metal halide salt mixture and mercury, the fill capable of sustaining an arc discharge between a pair of discharge electrodes situated at opposing ends of the discharge vessel. The discharge electrodes are connected to the base via frame wires and lead wires, which also support the discharge vessel. The particular combination of metal halide salts and their proportions in the salt mix largely determine lamp characteristics such as lumen output, the correlated color temperature (CCT), and the color rendering index (CRI) of the lamp.

The first generation of CDM lamps utilized a cylindrically-shaped PCA discharge vessel (also called an arc tube). These lamps typically exhibited luminous efficacy values of less than about 100 Lm/W, which is comparable to those of low to medium wattage QMH lamps. A newer generation of CDM lamps having shaped PCA discharge vessels have exhibited luminous efficacy values of 120 Lm/W or more. See International Patent Publication Number WO 2008/129466 A2. Since CDM lamps are generally superior to QMH lamps in lifetimes (up to 20,000 hours or more), color control, lumen maintenance (up to 80 percent) and color rendering (CRI values over 90), the finding of higher luminous efficacy values has led to investigation of CDM lamps for high wattage applications in which these lamps could compete with or even out perform existing QMH lamps in these applications. Thus, an opportunity exists for HW-CDM lamps to replace HW-QMH lamps in existing fixtures employing QMH-type ballasts which require lamp voltages of 200V or higher. However, there are at present no commercial CDM lamps on the market above about 600 watts. Moreover, existing CDM lamps operating at lamp voltages above 150V exhibit instabilities, color de-mixing, and arc bending.

SUMMARY OF THE INVENTION

The invention provides a design space for a high wattage CDM lamp which allows operation at the high voltages needed to retrofit the lamp into existing HW-QMH magnetic ballast systems, while at the same time minimizing arc bending and color de-mixing.

In accordance with the invention, it was found that the lamp voltage necessary to operate high wattage CDM lamps on HW-QMH ballasts is higher than that needed for a HW- QMH lamp of comparable wattage. Specifically, lamp voltage values for such HW-CDM lamps were found to fall within the range of about 200 to about 260 volts. Within this range, control of the electrode separation distance ED between the discharge electrodes in the discharge vessel as well as the amount of mercury (Hg) dose in the discharge vessel in accordance with the teachings of the invention results in arc bending in the vertical orientation of lamp operation of up to about 4 mm. In accordance with the broadest aspect of the invention, a high wattage (HW) ceramic gas discharge metal halide (CDM) lamp comprises: a ceramic discharge vessel with a central portion enclosing a discharge space, and a pair of end portions; a pair of discharge electrodes extending through the respective end portions into the discharge space; the discharge electrodes being separated by an electrode separation distance ED; a fill comprising a mixture of mercury (Hg), one or more metal halide salts including sodium halide (NaI) and an inert gas; and an outer glass envelope surrounding the discharge vessel, and a base, the outer glass envelope sealed to the base to form a gas-tight enclosure for the discharge vessel; characterized in that the mercury (Hg) is present in an amount within the range of about 75 mg to about 210 mg, the electrode separation distance ED is within the range of about 13 to about 23 mm, and the operating voltage is within the range of about 200 to about 260 volts, resulting in arc bending in the vertical orientation of operation of up to about 4 mm.

In an embodiment of the invention in which the nominal color temperature of the lamp is about 3000 K (referred to herein as 3K), the Hg is present in an amount within the range of about 115 mg to about 210 mg and the electrode separation distance ED is within the range of about 14 to about 23 mm. Preferably, the values for the amount of Hg and ED fall within the design space bounded by the points a, b, c and d, which are the points of intersection of lines defining the design limits of arc bending and voltage, respectively, as shown in Fig. 4, resulting in arc bending of from about 1 mm to about 3 mm. Most preferably, the values for the amount of Hg and ED fall within the design space bounded by the points a, e, f and d, which are the points of intersection of lines defining the design limits of arc bending and voltage, respectively, shown in Fig. 4, resulting in arc bending of from about 1 mm to about 2 mm.

In an embodiment of the invention in which the nominal color temperature of the lamp is about 4000 K (referred to herein as 4K), the Hg is present in an amount within the range of about 75 mg to about 170 mg and the electrode separation distance ED is within the range of about 13 to about 23 mm. Preferably, the values for the amount of Hg and ED fall within the design space bounded by the points a, b, c and d, which are the points of intersection of lines defining the design limits of arc bending and voltage, respectively, shown in Fig. 5, resulting in arc bending of from about 2 mm to about 4 mm. Most preferably, the values for the amount of Hg and ED fall within the design space bounded by the points a, e, f and d, which are the points of intersection of lines defining the design limits of arc bending and voltage, respectively, shown in Fig. 5, resulting in arc bending of from about 2 mm to about 3 mm. Such lamps are particularly useful in very high bay, warehouse, roadway, parking lot, and sports lighting applications.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be further elucidated with reference to the drawing in which:

Fig. 1 shows a high wattage (HW) ceramic gas discharge metal halide (CDM) lamp having a shaped PCA discharge vessel according to one embodiment of the invention;

Fig. 2 shows the shaped PCA discharge vessel of the embodiment of Fig. 1; Fig. 3 shows a high wattage (HW) ceramic gas discharge metal halide (CDM) lamp having a shaped PCA discharge vessel surrounded by a quartz shroud according to another embodiment of the invention;

Fig. 4 is a graphical representation of a design space of Hg dose (mg) versus electrode distance ED (mm) for a 3K CDM 750W lamp having high operating voltage and minimal arc bending according to one embodiment of the invention; and

Fig. 5 is a graphical representation of a design space of Hg dose (mg) versus electrode distance ED (mm) for a 4K CDM 750W lamp having high operating voltage and minimal arc bending according to another embodiment of the invention.

The Figures are diagrammatic and not drawn to scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 shows a high wattage (HW) ceramic gas discharge metal halide (CDM) lamp 10 having a PCA discharge vessel 12 including a central prolate spheroid-shaped portion 12a enclosing a discharge space 14, and a pair of tube-shaped end portions 12b and 12c. A pair of discharge electrodes 13a and 13b extend through the end portions 12b and 12c of the discharge vessel 12 into the discharge space 14. An outer bulb-shaped envelope 15 surrounds the discharge vessel 12 and discharge electrodes 13 and 14 and is sealed to a base 25 to provide an air-tight enclosure. Discharge vessel 12 and discharge electrodes 13 and 14 are supported within bulb-shaped envelope 15 by electrically conducting frame members 16, 17 and 18, which are in turn supported by electrically conducting supporting elements 19, 20 and 21. Supporting elements 19 and 20 are anchored by press seal 22, which maintains a vacuum or gas-filled environment within bulb-shaped envelope 15. Supporting element 21 is anchored by a dimple 15a at the top of the bulb-shaped enclosure 15.

Electrical leads 23 and 24 extending from base 25 are electrically connected to discharge electrodes 13 and 14 via supporting elements 19 and 20 and frame members 16, 17 and 18, respectively. A getter 26 is attached to the frame member 17.

The discharge space 14 is filled with an inert starting gas, mercury and a mixture of metal halide salts chosen to provide the desired luminous characteristics to the arc discharge.

Fig. 2 shows the electrode separation distance ED between the tips of the discharge electrodes 13a and 13b of the discharge vessel 12 of Fig. 1, as well as the distance d which measures arc bending as the amount of lateral displacement of the arc from the central axis A of the lamp electrodes. The prolate-spheriodal shape of the central portion (12a) of the discharge vessel (12) is designed to accommodate high internal pressure and provide minimal thermal gradients.

Fig. 3 shows another embodiment of the HW-CDM lamp 30 of the invention, which is similar to the embodiment of Fig. 1 , except that a cylindrically-shaped quartz containment shroud 32 is positioned to surround discharge vessel 120, to contain the discharge vessel and its contents in the event of lamp failure. Shroud 32 is secured in position by supporting elements 34 and 36. Antenna wire 38, typically molybdenum wire, wound around the outside wall of shroud 32, enhances mechanical strength of the shroud as well as the starting characteristics of lamp 30.

In accordance with the invention, it was found that the lamp voltage necessary to operate the HW-CDM lamp on HW-QMH ballasts requires a higher voltage than is required for a HW-QMH lamp of comparable wattage. For a CDM 750W lamps operating on a commercial CWA, M149 ballast (M149 is the ANSI designation for the QMH 750W lamp) the lamp voltage would have to be between 230 and 250 volts. A QMH lamp on the same ballast would only need to have a voltage of 200 volts. The higher voltage is required due to the lower power factor of the CDM lamp (about 0.75-0.85) compared to that of the QMH lamp (about 0.92-0.94). Some specific details of such a HW-CDM lamp operating at 240 volts that would operate at 750W on an M 159 ballast CWA ballast systems designed for QMH lamps and result in an acceptable level of arc bending. In the table, salt quantity is the amount of metal halide salts, Hg is the amount of mercury, ED is the distance between electrodes, Pf is the power factor, and arc bend is the amount of lateral displacement d of the arc from the central axis A of the lamp are given in Table I below.

Table I

3K 4K units

Salt Qty 70 80 mg

Hg 180 200 mg

ED 20 20 mm

ED*HG 3600 3600 mm

Volts 240 240 V

Pf 0 778 0 764

Arc Bend 0 4 0 6 mm

Example Several sample 750W CDM lamps of the type shown in Fig. 3 were made for testing, having 2-piece injection molded Er-doped PCA discharge vessels or arc tubes. This shaped arc tube had a wall thickness of 1.2mm and an OD of 24.5 mm, and a wall loading in the range of 24 W/cm²to 30 W/cm². Both 3K and 4K lamps were made with with Ar/Kr⁸⁵ as the fill gas, 80 mg of metal halide salts and various amounts of Hg in the arc tube, sealed in an ED37 outer bulb.

In general, the 3K salts have a lower voltage than 4K salts due to the greater NaI content. The 3K salts require about 40 mg higher Hg dose than the 4K salts for the same electrode distance.

Due to the relatively high pressure in this large arc tube - up to 25 bars - all lamps were made with a 28 mm ID x 70 mm quartz containment shroud wrapped with a moly coil.

Arc tube power was measured in both vacuum and gas filled environments and at four primary voltages - 200, 220, 240 (rated), and 260 volts. It was concluded that to achieve 750 watts on a M149 CWA, QMH ballast, a lamp voltage of about 240 volts is necessary. This corresponds to a Hg dose of about 110 mg for a 4K lamp and about 150 mg for a 3K lamp. These values will be somewhat different depending on the arc length and quantity of salts, and if the outer bulb is gas filled or not.

A vacuum outer bulb results in a 20 volt increase over a gas filled bulb; there is about a 5 volt per mm increase of arc length; 3K salts require about 50 mg greater Hg dose than a 4K design for the same electrode distance; the Hg dose results in about 1.2 volt/mg change. Lamp voltage and arc bending in vertical operation were measured and also modeled for both 3K and 4K lamps with different Hg doses and electrode separation distances ED. The 3000 K lamps have a different model than 4000 K lamps due to the differences in the metal halide salt dose chemistry; but mainly from differences in the NaI content. Analysis of the data revealed models that included the design factors: electrode separation distance (ED) and Hg dose. The model equations for voltage and arc bending are as follows:

Voltage = 1.18 Hg (mm) + 5.66 ED (mm) + 1.88 NaI (mg) - 4.98 NaI (%) Arc bending (mm) = 1.941 - 0.0298 Salts (mg) + 0.212 ED (mm) - 0.0782 NaI (%), where Salts is the total amount of metal halide salts in the discharge vessel, NaI (mg) is the amount of NaI in the Salts and NaI (%) is the weight percent of NaI in the Salts.

By collecting the models for the lamp voltage and arc bending, design spaces for both a 3K and a 4K CDM 750W lamp have been found, and are graphically represented in Figures 4 and 5.

Fig. 4 shows design spaces for a 750W CDM lamp optimized for 3K operation (color temperature of about 3000 K). A first design space is bounded by the points a through d, which are at the points of intersection of diagonal lines representing the lower and upper limits for voltage of 200 and 260 volts, with horizontal lines representing lower and upper limits of arc bending of 1 and 3 mm, respectively.

A second design space is bounded by the points a, e, f and d, which are at the points of intersection of diagonal lines representing the lower and upper limits for voltage of 200 and 260 volts, with horizontal lines representing lower and upper limits of arc bending of 1 and 2 mm, respectively. Fig. 5 shows design spaces for a 750W CDM lamp optimized for 4K operation (color temperature of about 4000 K). A first design space is bounded by the points a through d, which are at the points of intersection of diagonal lines representing the lower and upper limits for voltage of 200 and 260 volts, with horizontal lines representing lower and upper limits of arc bending of 2 and 4 mm, respectively. A second design space is bounded by the points a, e, f and d, which are at the points of intersection of diagonal lines representing the lower and upper limits for voltage of 200 and 260 volts, with horizontal lines representing lower and upper limits of arc bending of 2 and 3 mm, respectively. Photometry measurements were taken after 100 hours for three sets of 750W samples having 4-5 samples per set: 3K with gas in the outer bulb; 4K with gas in the outer bulb; and 4K with vacuum in the outer bulb. The results are shown as average values for each set in Table II.

Table II

The invention has necessarily been described in terms of a limited number of embodiments. From this description, other embodiments and variations of embodiments will become apparent to those skilled in the art, and are intended to be fully encompassed within the scope of the invention and the appended claims.

Claims

CLAIMS:

1. A high wattage ceramic gas discharge metal halide (CDM) lamp (10) comprising: a ceramic discharge vessel (12) with a central portion (12a) enclosing a discharge space (20), and a pair of end portions (12b, 12c); a pair of discharge electrodes (13, 14) extending through the respective end portions (12b, 12c) into the discharge space (14); the discharge electrodes (13, 14) being separated by a distance ED; a fill comprising a mixture of mercury (Hg), one or more metal halide salts including sodium halide (NaI), and an inert gas; an outer glass envelope (10) surrounding the discharge vessel (12), and a base (25), the outer glass envelope (10) sealed to the base (25) to form a gas-tight enclosure for the discharge vessel (12); characterized in that the Hg is present in an amount within the range of about 75 mg to about 210 mg, ED is within the range of about 13 to about 23 mm, and the operating voltage is within the range of about 200 to about 250 volts, resulting in arc bending in the vertical orientation of operation of up to about 4 mm.

2. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 1 in which the Hg is present in an amount within the range of about 115 mg to about 210 mg and ED is within the range of about 14 to about 23 mm, and the nominal color temperature of the lamp is about 3000 K (3K).

3. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 1 in which the Hg is present in an amount within the range of about 75 mg to about 170 mg and ED is within the range of about 13 to about 23 mm, and the nominal color temperature of the lamp is about 4000 K (4K).

4. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 2 in which the values for the amount of Hg and ED fall within a design space bounded by the points a, b, c and d, which are the points of intersection of lines defining the design limits of arc bending and voltage, respectively, as shown in Fig. 4, resulting in arc bending of from about 1 mm to about 3 mm.

5. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 2 in which the values for the amount of Hg and ED fall within a design space bounded by the points a, e, f and d, which are the points of intersection of lines defining the design limits of arc bending and voltage, respectively, as shown in Fig. 4, resulting in arc bending of from about 1 mm to about 2 mm.

6. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 3 in which the values for the amount of Hg and ED fall within a design space bounded by the points a, b, c and d, which are the points of intersection of lines defining the design limits of arc bending and voltage, respectively, shown in Fig. 5, resulting in arc bending of from about 2 mm to about 4 mm.

7. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 3 in which the values for the amount of Hg and ED fall within a design space bounded by the points a, e, f and d, which are the points of intersection of lines defining the design limits of arc bending and voltage, respectively, shown in Fig. 5, resulting in arc bending of from about 2 mm to about 3 mm.

8. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 1 in which the relationship between voltage, mercury (Hg) and electrode separation distance ED is defined by the equation: Voltage = 1.18 Hg (mm) + 5.66 ED (mm) + 1.88 NaI (mg) - 4.98 NaI (%), where NaI (mg) is the amount of NaI in the metal halide salts and NaI (%) is the weight percent of NaI in the metal halide salts.

9. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 1 in which the relationship between arc bending, mercury (Hg) and electrode separation distance ED is defined by the equation: Arc bending (mm) = 1.941 - 0.0298 Salts (mg) + 0.212 ED (mm) - 0.0782 NaI (%), where Salts is the total amount of metal halide salts in the discharge vessel, NaI (mg) is the amount of NaI in the Salts and NaI (%) is the weight percent of NaI in the Salts.

10. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 1 in which the metal halide salts are present in the amount of from about 70 mg to about 90 mg.

11. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 1 in which the shape of the central portion (12a) of the discharge vessel (12) is designed to accommodate high internal pressure and provide minimal thermal gradients.

12. The ceramic gas discharge metal halide (CDM) lamp (10) of claim 11 in which the shape of the central portion (12a) of the discharge vessel (12) is a prolate spheroid.