Arc instability

Arc instability

The arc of a xenon lamp is not completely stationary, and several additional factors will contribute to its instability:
Inadequate operating current
Excessive current ripple
Excessive inrush current
Excessive forced cooling
Improper lamp tilt
Advancing age of lamp

An outward appearance of arc instability is "flicker", which is a sudden change in useful light in a given application. Flicker can be caused by several factors, some of which are listed below:

Lamp current: Operating a lamp at low current causes the cathode tip to run to cold. This results in not enough electrons being supplied by the cathode tip, which causes the arc to move over the cathode tip surface looking for electrons. If the current is too high, the cathode tip runs too hot, which results in the evaporation of the thorium. The causes too few electrons to be emitted from the cathode, with resulting arc instability.
In-rush current: High in-rush currents on a repeated basis cause the erosion of the cathode tip, which leads to arc instability.
Bulb cooling: Excessive cooling of the bulb can cause thermal instability of the gas inside, which leads to turbulence and arc instability.
Start-up time: Immediately after lamp ignition, some instability occurs as the lamp components are heating up. This effect passes after a few minutes of operation.
Burning position: As specified in the section describing burning position, the closer to vertical a lamp is operated, the better its stability. As the lamp is operated off of its vertical or horizontal axes, the instability increases.
Lamp life: As a lamp progresses through its lifetime, one of the normal changes is the structure of the electrodes and a gradual increase in arc instability.
Focusing: Optimum performance of a xenon lamp in an optical system is when the cathode hot spot is positioned in the correct spot of the optical collector. If the lamp is not focused precisely and the tail of the arc is partially placed in the collection point of the optical collector, then flicker will result.



		Arc instability The arc of a xenon lamp is not completely stationary, and several additional factors will contribute to its instability: Inadequate operating current Excessive current ripple Excessive inrush current Excessive forced cooling Improper lamp tilt Advancing age of lamp An outward appearance of arc instability is "flicker", which is a sudden change in useful light in a given application. Flicker can be caused by several factors, some of which are listed below: Lamp current: Operating a lamp at low current causes the cathode tip to run to cold. This results in not enough electrons being supplied by the cathode tip, which causes the arc to move over the cathode tip surface looking for electrons. If the current is too high, the cathode tip runs too hot, which results in the evaporation of the thorium. The causes too few electrons to be emitted from the cathode, with resulting arc instability. In-rush current: High in-rush currents on a repeated basis cause the erosion of the cathode tip, which leads to arc instability. Bulb cooling: Excessive cooling of the bulb can cause thermal instability of the gas inside, which leads to turbulence and arc instability. Start-up time: Immediately after lamp ignition, some instability occurs as the lamp components are heating up. This effect passes after a few minutes of operation. Burning position: As specified in the section describing burning position, the closer to vertical a lamp is operated, the better its stability. As the lamp is operated off of its vertical or horizontal axes, the instability increases. Lamp life: As a lamp progresses through its lifetime, one of the normal changes is the structure of the electrodes and a gradual increase in arc instability. Focusing: Optimum performance of a xenon lamp in an optical system is when the cathode hot spot is positioned in the correct spot of the optical collector. If the lamp is not focused precisely and the tail of the arc is partially placed in the collection point of the optical collector, then flicker will result.