What kind of built-in light meters in film cameras exist?

Question

There are a number of light meters built into film cameras I am aware of.

First there's selenium cell light meters, like on the below old Canonet.

Later cadmium sulphide (CdS) photocells became more common. This later Canonet model used one. It's right above the lens' front element.

After that silicon photocells started becoming the norm, with increasingly complex segmented meters using through-the-lens metering offering options such as center-weighted average metering, partial metering, spot metering and evaluative (Canon) or matrix (Nikon) metering.

Apart from the above types of meters (selenium cell, CdS cell, TTL silicon multi-segment), what other built-in meters did film cameras use? Is there some exhaustive list with useful categories?

(all images courtesy of Wikimedia Commons)

Answer 1

In addition to the electric types mentioned, there were also early chemical (actinometer) and purely optical (extinction meter) designs.

Some modern digital camera designs however will use the (CMOS or CCD) imaging sensor itself as a light meter (which is technically speaking a silicon photodiode based meter).

Also, mind that there were multi-segment CDS designs, some of which were also TTL (both to be found in the Minolta SR-T series).

In theory, electric light meters COULD also have employed gallium arsenide cells, silicon or other non-selenium solar cells in special cases.

EDIT: Or germanium photodiodes/phototransistors.

Answer 2

That's it, as far as I know. Selenium, Cadmium, Silicon.