Photoluminescent material is not new. It is the stuff in your kid’s ceiling stars, in old wristwatch dials, in every glow stick you have ever cracked at a concert. What is new is putting that decades old chemistry on the back of a flagship smartphone and letting the owner become the artist instead of the factory. That is exactly what Redmi did with the K100 Pro, and it might be the single most fun thing to happen to phone design all year, mostly because it does not take itself too seriously.
The finish is called Glowing Firefly, and it works by hiding a luminescent layer between the phone’s glass back and its green ink coating, invisible in daylight and glowing wherever you point a flashlight or light pen after dark. Redmi launched the K100 Pro in China on August 11, pairing the party trick with a legitimately serious spec sheet that includes a 185Hz OLED, a Snapdragon 8 Elite Gen 5 V Series chip, and a 200MP camera. The phone can keep up with any flagship on paper. It just also happens to double as a doodle pad.
Designer: Xiaomi
Redmi’s own language calls the back panel a light painting canvas, and that description holds up better than most marketing copy tends to. Point a flashlight, a laser pointer, or a dedicated light pen at the glass and the material soaks up the energy along the exact path the light traveled, then releases it slowly as a glowing outline. Write your name, sketch a smiley face, sign the thing like a yearbook, and watch it fade out over the following minutes. There is no chip involved, no battery drain, nothing to charge separately. It is closer to a Lite Brite than to anything Qualcomm builds, which is honestly the charm of it.
Nothing tried something adjacent with the , and I still think about that phone. It used a green phosphorescent coating along the ribbon cables and camera trim, charged by ambient light and glowing softly on its own without any input from you. It was quiet, tasteful, very on brand for a company obsessed with making internals look intentional. Redmi took that same chemistry and handed the pen to the user instead of the factory. One phone glows because the designers told it to. The other glows because you told it to, and that distinction matters more than it sounds.
None of this changes what the K100 Pro is underneath the finish, a genuinely stacked gaming flagship with an 8,580mAh battery, 100W charging, and a cooling system built for long sessions. But the spec sheet was never going to be the reason anyone remembers this phone. The reason is a green slab that lets you leave a temporary signature in light, fading like sidewalk chalk, gone by morning, ready for you to draw on it again tomorrow.
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