Method of starting an HID lamp and ballast incorporating same

1. A method for starting an HID lamp using an igniter circuit, comprising the steps of:

(a) obtaining a cumulative probability function of breakdown times, P(t), for the lamp at a voltage, V;

(b) determining a minimum pulse length, T p , for a selected probability of ignition, P ign ;

(c) if the lamp is operable at the minimum pulse length, then operating the lamp with a DC pulse having a duration T p and voltage V;

(d) or alternatively, if the lamp is not operable at the minimum pulse length, then determining a relaxation time, T rel , for a burst mode, selecting a probability of ignition per burst, P b , calculating a minimum number of pulses, n p , in a burst, determining a number of bursts, N b , for the selected probability of ignition, and operating the lamp in the burst mode with N b bursts separated by relaxation time, T rel , with each burst having n p pulses of voltage V.

2. The method of claim 1 , wherein the igniter circuit is switched to operate in a continuous pulse mode after the lamp ignites in the burst mode.

3. The method of claim 2 , wherein the continuous pulse mode continues for the remainder of a takeover phase after which the igniter circuit is shut down.

4. The method of claim 1 wherein the cumulative probability function of breakdown times is obtained by repeatedly applying a fast-rise DC pulse to the lamp at the voltage V and measuring a breakdown time.

5. The method of claim 4 wherein the application of the DC pulse and the measurement of the breakdown time is repeated for between about 1000 to about 5000 times.

6. The method of claim 1 wherein the selected probability of ignition is at least 95%.

7. The method of claim 1 wherein the selected probability of ignition is at least 99%.

8. A ballast for operating a high intensity discharge lamp, the ballast having an igniter circuit and an igniter control circuit, the igniter circuit generating voltage pulses having a magnitude V, duration T 1 , and spaced T 2 apart, the igniter control circuit repeatedly causing the igniter circuit to apply bursts of the voltage pulses to the lamp by cycling the igniter circuit on for a period of about n p ·(T 1 +T 2 ) where n p · is a minimum number of pulses for a selected probability of ignition per burst and then off for a relaxation time of T rel , the igniter control circuit repeating the cycle until a first breakdown in the lamp.

9. The ballast of claim 8 , wherein the igniter control circuit switches the igniter circuit to a continuous pulse mode after the first breakdown.

10. The ballast of claim 9 , wherein the igniter control circuit turns the igniter circuit off when a thermionic arc is established in the lamp.

11. A ballast for operating a high intensity discharge lamp, the ballast having an igniter circuit and an igniter control circuit,

the igniter control circuit obtaining a cumulative probability function of breakdown times, P(t), for the lamp by repeating causing the igniter circuit to apply a fast-rise DC voltage pulse of magnitude V to the lamp and then measuring and storing a breakdown time, T B , for each voltage pulse applied;

the igniter control circuit using the cumulative probability function of breakdown times to determine a minimum pulse length, T p , for a preselected probability of ignition, P ign ;

the igniter control circuit determining if the lamp is operable at the minimum pulse length, and then, if the lamp is operable at the minimum pulse length, operating the lamp by causing the igniter circuit to apply to the lamp a DC pulse having a duration T p and voltage V;

or alternatively, if the lamp is not operable at the minimum pulse length, the igniter control circuit determining a relaxation time, T rel , for a burst mode, calculating a minimum number of pulses, n p , in a burst for a preselected probability of ignition per burst, P b , determining a number of bursts, N b , for the preselected probability of ignition, P ign , and causing the igniter circuit to operate the lamp in the burst mode with N b bursts separated by relaxation time, T rel , with each burst having n p pulses of voltage V.

12. The ballast of claim 11 , wherein the igniter control circuit obtains the cumulative probability function of breakdown times by applying the fast-rise DC pulse about 1000 to 5000 times.

13. The method of claim 11 , wherein the igniter control circuit switches the igniter circuit to operate in a continuous pulse mode after the lamp ignites in the burst mode.

14. The method of claim 13 , wherein the continuous pulse mode continues for the remainder of a takeover phase after which the igniter circuit is shut down by the igniter control circuit.

15. The method of claim 11 wherein the preselected probability of ignition is at least 95%.

16. The method of claim 11 wherein the preselected probability of ignition is at least 99%.