It means “may you always keep your inner joy, warmth, personality, and sense of self.” It’s a kind wish that the person never becomes dull, discouraged, or emotionally drained.

What “light” means

“Light” usually stands for goodness, hope, kindness, confidence, or the positive energy someone carries. In this kind of phrase, it’s not literal light, but a metaphor for what makes someone feel vibrant and alive.

What “spark” means

“Spark” points to energy, passion, charm, creativity, or that special thing that makes someone feel uniquely themselves. Saying “never lose your spark” is basically saying, “keep that lively part of you.”

How it sounds in practice

People often say this when they want to encourage someone who seems tired, stressed, or going through a hard time. It can also be a warm compliment, meaning the speaker sees something bright and beautiful in the other person.

Simple paraphrase

A natural plain-English version would be: “I hope you always stay true to yourself and keep your inner brightness and energy.”

TL;DR: It’s a poetic way of wishing someone keeps their positivity, spirit, and authentic self.