transmission vs transmittance

transmission and transmittance both are nouns.

Word	Noun	Adjective	Verb	Adverb
transmission	Yes	No	No	No
transmittance	Yes	No	No	No

As nouns, transmission and transmittance are synonyms defined as:

transmission and transmittance: the fraction of radiant energy that passes through a substance

transmission (noun)	transmittance (noun)
the act of sending a message; causing a message to be transmitted	the fraction of radiant energy that passes through a substance
the gears that transmit power from an automobile engine via the driveshaft to the live axle
communication by means of transmitted signals
an incident in which an infectious disease is transmitted
the fraction of radiant energy that passes through a substance