This is another character contrast trope. Unlike the Tomboy And Girly Girl trope, both female characters are decidedly feminine - but in different ways. Light Feminines (Sweet and Serene) are generally angelic, conservative, and feels love - which Dark Feminines (Sexy and Sassy) are generally devilish, liberal, and plays with desire. In short, Light Feminines exude the aspects of traditional femininity - while Dark Feminines are feminine in a much less innocent fashion. Either type can be the Girly Girl portrayed in the Tomboy And Girly Girl contrast.

Related to Madonna Whore Complex and The Three Faces Of Eve (Child/Wife=Light; Seductress=Dark). In a Betty And Veronica love triangle, Betty is usually the Light Feminine - with Veronica being the Dark Feminine. Also, the Light Feminine is typically the Blue Oni - while the Dark Feminine is typically the Red Oni.

Examples:

• My Little Pony Friendship Is Magic: Fluttershy (Light) is kind, caring, very much like a mother to the animals. Rarity (Dark) is vain and bratty, though not quite as much so as she seems.
• Non Sequitur: Kate is the Light Feminine, while Danae is the Dark Feminine.
• Overlord: The potential queens fall into this. In the second game, the first two mistresses fall into Tomboy And Girly Girl - but also serve as a collective "Light Feminine" to the third.
• Catherine: Catherine is the Dark Feminine, while Katherine is the Light Feminine.
• Adventure Time: Marceline is the Dark Feminine, while Bubblegum is the Light Feminine.
• Final Fantasy X: Lulu is the Dark Feminine, while Yuna is the Light Feminine.
• Glee: (Male example) Blaine Anderson (Light) and Kurt Hummel (Dark). Blaine is kind, nurturing, generous, and little oblivious, Kurt is prissy, bitchy, arrogant, entitled, self-absorbed.
• Gone With The Wind: Melanie is the Light Feminine, while Scarlett is the Dark Feminine.
• Dragon Age Origins: Leliana is the Light Feminine, while Morrigan is the Dark Feminine.
• Sunrise: The Woman from The City is the Dark Feminine (hedonist, cheater), while The Wife is the Light Feminine (goodie goody all the way through).
• Gentlemen Prefer Blondes: Russell is the Dark Feminine, while Monroe is the Light Feminine.