The first thing people remark on is the honeycomb matrix encircling the lens. The “EE” stands for “Electric Eye,” and the “Matic” indicates the automatic exposure made possible by the selenium cells behind that glass.
The matrix of convex “bubbles” directs light at the selenium cell or cells in a predictable way, both in terms of amount and direction. This ensures that the light being measured is actually coming from the direction of the subject, and helps ensure that the light being sampled is a consistent fraction of the light available so it can be accurately be measured every time.
Selenium, a key component in solar panels, is photovoltaic — meaning when it is exposed to light, “electrons are knocked loose from the atoms,” (NASA’s words, not mine) producing an electrical current. The current is tiny, but measurable, and is consistent for a given amount of light.
What’s cool about this is that selenium light meters don’t need batteries to operate. Eventually the selenium cell wears out — essentially there is a predetermined number of photons a given amount of selenium can absorb and convert into electric current before it ceases to function — but that can be a very long time if you keep the meter matrix covered when not in use.