DIRECTIONAL 



ANTENNA 



F'jg. 10-3 Viewing lights, camera and strobe ligtil. and tioming antennae clustered on the brow of SEA OTTER- (Arctic Manne) 



Mercury Vapor — A gas discharge light that 

 produces light by passing a current through 

 mercury vapor under pressure. 



Thallium Iodide — Similar to the mercury 

 vapor light, but with the addition of thallium 

 to the mercury in the arc tube to increase 

 lumen efficiency and produce a different 

 spectral output. 



Incandescent lights radiate throughout 



the visible portion of the spectrum and con- 

 centrate most of their energy in the red area. 

 The mercury principal line is at approxi- 

 mately 4,400 Angstroms (blue); the thallium 

 line is at approximately 5,350 Angstroms 

 (green). Referring again to Figure 10.4, it is 

 seen that the gas discharge lights produce a 

 color spectrum least attenuated by absorp- 

 tion. 



473 



