Am a guy, planning to get this tattooed and coming from a Latin-illiterate background (never studied Latin in my life). Context: to remind me of God's guidance throughout my life and to continue to trust in Him. More context from the bible can be found in John 8:12, where it says "I am the light of the world. Whoever follows me will never walk in darkness, but will have the light of life."
I did a Google translate from English to Latin and it shows, "Lux aeterna rector mihi". However, digging further I also found that "lucis" can also mean light and "aeternus" is basically the masculine version of "aeterna". (Need verification on this)
Also, just out of curiosity, the modern Italian translation (again from google) reads "la luce eterna mi guidi", and I can't help but to wonder how did this evolve from traditional Latin. It's pretty interesting.