RatioMaster

Lamp Power Supply

PTI lamp power supplies are highly-regulated DC units that provides very stable power for xenon, mercury, and mercury/xenon compact arc lamps as well as tungsten-halogen lamps.

Specifications

Lamp power capacity: 75 to 200 watts
Height: 100 mm (3.9 inches)
Width: 100 mm (3.9 inches)
Length: 210 mm (8.3 inches)
Weight: 1.9 kg (4.2 pounds)
Window diameter (D): 65 mm

Technical Information on Lamps

Compact Arc Lamps
High pressure gas discharge lamps having an arc length which is small compared with the size of the electrodes are called short arc or compact arc lamps. Depending on rated wattage and intended application, the arc length of these lamps may vary from about a third of a millimeter to about a centimeter. These lamps have the highest luminance and radiance of any continuously operating light source and are the closest approach to a true "point" source.

The envelope is made from optically clear quartz material of various grades and has a spherical or ellipsoidal shape. The grade of the quartz will determine the amount of ozone generated. The most widely used material for the electrodes is tungsten.

Most compact arc lamps are designed for DC operation. This results in better arc stability and substantially longer life. DC systems consist of an igniter and a regulated power supply. High voltage pulses (up to 50,000 volts) break down the gap between the electrodes, ionize the gas and heat the cathode tip to thermionic emitting temperatures.

Note that higher wattage lamps do not necessarily yield more light intensity. When higher illumination intensity is needed, lamps must be selected with greater brightness, and this does not always increase with lamp wattage.

Xenon Lamps
Xenon compact arc lamps are filled with several atmospheres of xenon gas. They reach 80% of final output within 10 minutes or less of starting. The arc color is very close to daylight (6000 deg. K). The spectrum is continuous in the visible range and extends far into the ultraviolet. A Xenon lamp exhibits strong lines in the near infrared between 800 and 1000 nm and some weak lines in the blue portion of the spectrum.

Xenon compact arc lamps are made with rated wattages from 75 to 30,000 watts and are available for operation in either a vertical or horizontal position. The breakdown voltage between the electrodes will run from 10kv for a small lamp up to 60kv or more for lamps rated 30kw.

The luminous efficacy of Xenon compact arc lamps is approx. 30 lumens per watt at 1000 watts, 45 lumens per watt at 5000 watts, and over 150 lumens per watt at 20kw.

Polarization
Some lamps can only be mounted one way in the PowerArc housing since the anode (+) and cathode (-) have different diameters, thus making accidental polarization reversal nearly impossible. However, some lamps have the same diameter anode and cathode, allowing room for error. Refer to the lamp manufacturer's data sheet for proper identification of the anode and cathode.

Note that reversed polarization will result in immediate and permanent damage to the lamp electrodes. A lamp that has been fired with reversed polarization will have obvious physical damage to the electrodes. A damaged lamp will fire, but it will exhibit unstable performance and a severely shortened operating life.

Lamp Stability
Short term stability is measured over seconds, while long term stability is measured over minutes, hours, or even days.

Short term stability is affected by arc "wander," "flare" and "flutter." Arc wander is the movement of the attachment point of the arc on the cathode surface. Typically the arc moves around the conical cathode tip in a circular fashion, taking several seconds to move a full circle. Arc flare refers to the momentary change in brightness as the arc moves to an area on the cathode having a preferential emissive quality over the previous attachment point. Arc flutter is the rapid side-to-side displacement of the arc column as it is buffeted by convection currents in the xenon gas which are caused as the gas is heated by the arc and cooled by the envelope walls.

Arc wander and flare can be reduced by a slight decrease in the operating current. For example, a 75 watt xenon lamp rated at 5.4 amps may be operated at 4.5 amps for the first one or two minutes of operation, after which the current should be brought up to the specified normal operating level.

Lamp Life
The useful life of compact arc lamps is determined primarily by the decrease of luminous flux caused by the deposit of evaporated electrode material on the inner wall of the envelope. Frequent ignition accelerates electrode wear and hastens the blackening of the envelope. Average lamp life is based on approximately 20 minutes of operation for each ignition. The end of the lamp life is the point at which the UV output has decreased by approximately 25%, the arc instability has increased beyond 10%, or the lamp has ceased to operate under specified conditions. Lamps should be replaced when the average lamp life has been exceeded by 25%.

As the lamp ages, the operating voltage will increase. Lamp current should be decreased to maintain output until the minimum operating current is reached. At this time the lamp should be replaced.

Lamp life varies with different types. Check the manufacturer's specifications for the rated lamp life.