||The long arc Krypton lamp is manufactured solely for one very special application - the optical pumping of Neodymium : YAG lasers. Their strong shortwave infra-red radiation between 750 and 900nm is perfectly suited to this application. As a light source however, the krypton discharge is rather inefficient, achieving only some 30 lumens per watt. Like xenon, its emission spectrum is fairly well balanced over the visible 380-780nm range, thus the light has a whiteish appearance and the colour rendering properties are good by comparison with other pure gas discharge lamps.
In view of the very large amount of power dissipated in such slim light sources as these, it is essential that they are cooled with a rapid flow of deionised water. Failure to provide sufficient water cooling rate results in the instantaneous destruction of the lamps - they explode. During life, the quartz devitrifies quickly, particularly in the area around the electrodes. Hairline cracks and other defects migrate both towards the centre of the tube and through the wall thickness, and ultimately the lamps fail by shattering.
Lamps are for operation on DC only and as such have specially formed electrodes at each end. The cathode has a sharply pointed tip whilst the anode electrode has a ball end. Both are machined from solid tungsten rod and can be seen in the detailed thumbnail photographs to the left. The bulb is fabricated from high purity quartz and via three intermediate graded sealing glasses, it is sealed directly to the electrode shank at either end of the tube. The flattened area of the exhaust tube tip can be seen beside the cathode.