I get lots of questions via email from people wanting to know how to use a lensatic compass, and I think I've covered that pretty well in a series of two posts. They give the basics of how they work, how to shoot an azimuth, how to get a bearing, and so on. After reading those two articles anyone should be able to go out and perform basic land navigation with a map and lensatic compass.
What I haven't covered in much detail is some of the nuances of lensatic compasses, such as the tips and tricks to getting the most out of them in the field. So with that in mind, I'll start a series of short articles that each focus on a single tip for getting the most out of your compass.
This one will deal with night and low light navigation, a topic that could span several lengthy articles on its own. I'll get around to that one of these days.
Most people are aware that lensatic compasses are fitted with small amounts of tritium around the dial. This is a low level radioactive isotope that is used in a multitude of applications where self-powered illumination is necessary. It has replaced radium in recent decades after it was discovered that radium exposure is linked to an increased occurrence of bone cancer.
Tritium is considered safe for external use because it is a weak beta particle emitter - so weak in fact that the radiation it emits cannot penetrate human skin. Have no fear, the science here is sound a proven.
It has a half life of about 12 years. This means that at around the 12 year mark, the tritium in your lensatic compass will have radiated about half the energy that it has to offer. At the 24 year mark it will be another half of that, and so on. So the tritium will continue emitting "light" for quite a long time before it goes completely dark.
If the tritium in your compass has become dim such that you can't read the compass at night, you can "charge" it up with any flashlight. In the event that you're under strict light discipline (in a military setting, for example) you can simply sup your hands around the compass and the head of the flashlight so that no light escapes. Putting the two in a opaque bag or enclosure is effective as well.