1. Optical study of the breakdown phenomenon in High Intensity Discharge lamps
Freddy Manders, Marco Haverlag
Philips Lighting Eindhoven
Paul Aben, Job Beckers, Winfred Stoffels
Technical University of Eindhoven

2. Outline Introduction Experimental Set-up Experimental results
HID lamps
Background
approach
Experimental Set-up
Power supply
Lamps under investigation
Experimental results
DC ignition of low aspect lamps
DC ignition of High aspect lamps
AC ignition
Conclusions

3. Philips One of the biggest lamp manufactures in the world
In Eindhoven pre-development of all lighting sources
Halogen
Fluorescent
Compact fluorescent
LED
HID
etc
Introduction
Experimental
set-up
results
Conclusions

4. PRACTICAL APPLICATIONS
USED FOR:
High efficiency
High colour rendering
PRACTICAL APPLICATIONS
Stadiums
Tennis courts
Parking lots
Automotive
Shopping malls
Beamers
Introduction
Experimental
set-up
results
Conclusions
Burner is filled with:
Starting gas (Noble gases, e.g. Xe & Ar)
Buffer gas (e.g. mercury)
Radiation emitting substance (e.g. Na, Ce, Dy, Ca, …)

5. We need to lower the ignition voltage of the gas discharge
Background
HID lamps Ignition voltage
~ 4 kV (300 mBar, pulse ignition, standard HID lamps)
~ 18 kV (10 Bar Xe, pulse ignition, Automotive lamps)
Issues
1 st electron, small lamps ( Automotive, UHP)
insulation materials (cables, lamp cap, etc)
Safety issues, bigger lamps
More expensive electronics
The lamp should always ignited
We need to lower the ignition voltage of the gas discharge
Introduction
Experimental
set-up
results
Conclusions

6. Approach Try to understand how breakdown in HID lamps happens
Study breakdown process in model lamps with an ICCD camera and change a few parameters
Gas type (Ar / Xe)
Gas pressure (300 mBar, 700 mBar )
Length / diameter of the lamp
Positive / negative voltage
Voltage source (Pulse, AC)
Introduction
Experimental
set-up
results
Conclusions

7. Experimental set-up Introduction Experimental set-up results
Conclusions

8. Experimental set-up Lamps Voltage source Low aspect ratio burners
Argon, p = 300 mbar, d = 7 mm
High aspect ratio burners
Diameter = 4 mm
Argon and Xenon
electrode distance: 1.5 cm and 2.7 cm
300 mbar and 700 mbar
Introduction
Experimental
set-up
results
Conclusions
Pulse source of 5 kV with a rise time of 10 nsec.
AC voltage source from 25 kHz up to 3 MHz
Voltage (kV)

9. Experimental results DC pulse ignition of low aspect lamps
DC pulse ignition of high aspect lamps
AC ignition
Introduction
Experimental
set-up
results
Conclusions

10. Low aspect ratio: Argon 300 mBar, -4.0 kV
High voltage side
Grounded side
17 ns
0 ns
6 ns
12 ns
Introduction
Experimental
set-up
results
Conclusions
18 ns
3 ns
7 ns
13 ns
19 ns
4 ns
9 ns
14 ns
21 ns
5 ns
10 ns
15 ns
max

11. Low aspect ratio: Argon 300 mBar, -4.0 kV
Introduction
Experimental
set-up
results
Conclusions
9 nsec
High voltage ionization expands spherical
High voltage ionization is not uniform, channels are visible, streamers.
Grounded emission becomes, because of the interaction with the wall

12. Low aspect ratio: Argon 300 mBar
-4.0 kV
-3.0 kV
-2.5 kV
20 nsec
41 nsec
59 nsec
73 nsec
99 nsec
7 nsec
11 nsec
16 nsec
17 nsec
21 nsec
16 nsec
29 nsec
40 nsec
51 nsec
59 nsec
Introduction
Experimental
set-up
results
Conclusions

13. Low Aspect ratio: Argon 300 mBar, -2.5 kV
Introduction
Experimental
set-up
results
Conclusions
59 nsec
High voltage emission region expands spherical
High voltage emission region is diffuse, burner is almost completely filled with ionization
No grounded electrode emission is visible

14. Low aspect ratio: Argon 300 mBar
-4.0 kV
+4.0 kV
+2.5 kV
2 nsec
7 nsec
39 nsec
Introduction
Experimental
set-up
results
Conclusions
6 nsec
11 nsec
60 nsec
8 nsec
16 nsec
99 nsec
17 nsec
11 ns
128 nsec

15. Low aspect ratio: Argon 300 mBar
-4 kV
+4 kV
+2.5 kV
Introduction
Experimental
set-up
results
Conclusions
16 nsec
8 nsec
99 nsec
In all 3 pictures mechanism is streamer
Negative streamers are in general more diffuse.
+4 kV: clearly streamer mechanism
+2.5 kV: slower and more diffuse

16. Conclusions low aspect ratio lamps
At high negative over voltage (-4 kV)
discharge is a streamer
For lower voltage there is a transition
to a Fast Ionisation wave (-2 kV)
Negative streamers are more diffuse then positive
Discharge always starts at powered electrode because of interaction with wall
Introduction
Experimental
set-up
results
Conclusions

17. High aspect ratio burners
Argon, p = 300 mbar, d = 1.5 cm, V = +4kV
Introduction
Experimental
set-up
results
Conclusions
0 ns
52 ns
94 ns
8 ns
58 ns
99 ns
15 ns
69 ns
107 ns
23 ns
75 ns
109 ns
25 ns
84 ns
121 ns
39 ns
85 ns
48 ns
93 ns

18. High aspect ratio burners: Ar300 mBar, +4kV
Introduction
Experimental
set-up
results
Conclusions
85 nsec
streamer along burner wall
very little branching
grounded emission expands spherical and is diffuse

19. High aspect ratio burners: +4kV
Ar 300 mBar
Ar 700 mBar
Xe 300 mBar
23 ns
52 ns
75 ns
85 ns
121 ns
109 ns
99 ns
23 ns
51 ns
71 ns
85 ns
115 ns
98 ns
89 ns
22 ns
39 ns
57 ns
85 ns
140 ns
135 ns
106 ns
Introduction
Experimental
set-up
results
Conclusions

20. High aspect ratio burners: +4kV
85 nsec, Ar 300 mBar
Introduction
Experimental
set-up
results
Conclusions
85 nsec, Ar 700 mBar
85 nsec, Xe 300 mBar
Ar300: little branching, intense emission at grounded electrode
Ar700: much branching
Xe300: much branching, very little emission at grounded electrode

21. High aspect ratio burners: Ar 700 mBar - 4kV
Introduction
Experimental
set-up
results
Conclusions
0 ns
97 ns
269 ns
9 ns
108 ns
272 ns
20 ns
143 ns
301 ns
21 ns
188 ns
303 ns
29 ns
212 ns
313 ns
39 ns
242 ns
320 ns
257 ns
54 ns
340 ns

22. High aspect ratio burners: -4kV
Introduction
Experimental
set-up
results
Conclusions
257 nsec
High voltage ionization (negative voltage) very diffuse and at a very low intensity
At grounded electrode streamers are formed
Two different mechanisms during one discharge

23. Conclusion high aspect lamps
More interaction with the wall because the distance to the wall is smaller
Positive discharge branch more then negative
Negative discharge is more diffuse and slower
The higher the pressure the more branching
Xe branches more then Ar
Introduction
Experimental
set-up
results
Conclusions

24. Comparison of velocities at + 4 kV
velocity / (106 m/s)
d = 1.5 cm
d = 2.7 cm
Ar300
1.9 ± 0.1
1.6 ± 0.1
Ar700
1.3 ± 0.1
1.1 ± 0.1
Xe300
1.7 ± 0.1
1.4 ±0.1
Xe700
1.2 ± 0.1
1.0 ± 0.1
Introduction
Experimental
set-up
results
Conclusions

25. Comparison of velocities at + 4 kV
velocity / (106 m/s)
d = 1.5 cm
d = 2.7 cm
Ar300
1.9 ± 0.1
1.6 ± 0.1
Ar700
1.3 ± 0.1
1.1 ± 0.1
Xe300
1.7 ± 0.1
1.4 ±0.1
Xe700
1.2 ± 0.1
1.0 ± 0.1
Introduction
Experimental
set-up
results
Conclusions
1.2
1.2
1.2
1.2

26. Comparison of velocities at + 4 kV
velocity / (106 m/s)
d = 1.5 cm
d = 2.7 cm
Ar300
1.9 ± 0.1
1.6 ± 0.1
Ar700
1.3 ± 0.1
1.1 ± 0.1
Xe300
1.7 ± 0.1
1.4 ±0.1
Xe700
1.2 ± 0.1
1.0 ± 0.1
Introduction
Experimental
set-up
results
Conclusions
1.4
1.4
1.4
1.4

27. Comparison of velocities at + 4 kV
velocity / (106 m/s)
d = 1.5 cm
d = 2.7 cm
Ar300
1.9 ± 0.1
1.6 ± 0.1
Ar700
1.3 ± 0.1
1.1 ± 0.1
Xe300
1.7 ± 0.1
1.4 ±0.1
Xe700
1.2 ± 0.1
1.0 ± 0.1
Introduction
Experimental
set-up
results
Conclusions
1.2
1.1
1.1
1.1

28. Conclusions velocity measurements
Out of the camera pictures it is possible to calculate the velocity of the discharge. The speed are all in the order of 10^6 m/s which is normal for a streamer discharge
The velocity results for the high aspect ratio lamps with 4 kV show that there are some relations:
Introduction
Experimental
set-up
results
Conclusions
The factor the velocity changed
Distance between electrodes changed from 1.5 cm to 2.7 cm
1.2
Gas pressure changed from 300 to 700 mBar
1.4
Gas type changed from Ar to Xe
1.1

29. Breakdown voltage for AC ignition for high aspect lamps
Introduction
Experimental
set-up
results
Conclusions
-29%
-26%
For DC pulse ignition ~ 4 kV is needed to ignited the 700 mBar Xe lamps so AC lowers the breakdown voltage with ~ 50 %

30. Experimental results (AC ignition - Xenon)
Two regimes in which the burners can ignite
Introduction
Experimental
set-up
results
Conclusions

31. Experimental results of 300 mBar Xe (AC ignition)

32. Discharge travels via the wall
700 mBar of Xe
30kHz
Low frequencies:
Discharge travels via the wall
Looks like pictures of pulse ignition (streamer-like channels, branching)
80kHz
Introduction
Experimental
set-up
results
Conclusions
140kHz
High frequencies:
Discharge travels through the gas
Ionisation channel has the shape of a streamer …
200kHz
300kHz
400kHz

33. Maximum velocity of ionisation front:
300 mBar Xenon at 200 kHz
Introduction
Experimental
set-up
results
Conclusions
Maximum velocity of ionisation front:
Contradiction:
Shape looks like a streamer-like discharge
Maximum velocity of the ionisation channel is in the order of those in Townsend discharges.

34. Conclusions on AC ignition
AC ignition voltage about 50-60% lower than pulse ignition voltage
Ignition voltage is a decreasing function of frequency
At relatively low frequencies the ionisation channel travels along the wall
At relatively high frequencies the ionisation channel travels through the gas
Ionisation channel builds up step-wise over many periods
Ionisation channel only grows during voltage maximum
Introduction
Experimental
set-up
results
Conclusions
Possible explanation: Due to alternating E-field more charged particles stay in the volume, and are able to ionise for a longer time.
The higher the frequency, the more charged particles stay in the volume.

35. Thank you for your attention!