'light-reliant' originates as a compound of the English words 'light' and 'reliant'. 'light' comes from Old English 'līht' meaning 'light, brightness', and 'reliant' derives from the verb 'rely' (from Old French 'relier'), ultimately from Latin 'religāre' meaning 'to bind'.

'rely' changed from Old French 'relier' and Middle English forms such as 'relien' into the modern verb 'rely', and the adjectival form 'reliant' (verb + -ant) developed in Modern English; the compound 'light-reliant' is a relatively recent descriptive formation in Modern English combining 'light' + 'reliant'.

Initially, elements of the root (from Latin/Old French) had senses related to 'binding' or 'fastening', but over time 'rely' shifted to mean 'to depend on', and the combined form 'light-reliant' came to mean 'depending on light'.