Here are some possibilities:
If "lourde" refers to weight:
* Léger(e) - light
* Facile(e) - easy
* Simple(e) - simple
If "lourde" refers to atmosphere or feeling:
* Léger(e) - light
* Joyeux(euse) - joyful
* Heureux(euse) - happy
* Gai(e) - cheerful
If "lourde" refers to something being difficult or demanding:
* Facile(e) - easy
* Simple(e) - simple
* Léger(e) - light
* Agréable(e) - pleasant
It's essential to consider the specific context to determine the most accurate opposite for "lourde".