Glow in the Dark Cake Recipe (With Tonic Water and Neon Frosting)

A glow in the dark cake uses tonic water (which contains quinine and fluoresces blue-white under UV light) in the frosting, combined with neon food coloring that also reacts to UV light. The result is a cake that glows brilliantly under a black light — perfect for Halloween, glow parties, space-themed birthdays, and New Year’s Eve.

Table of Contents

• How the Glow Effect Works
• What You Need
• The Cake
• The Glowing Buttercream
• Decorating for Maximum Glow
• Tips
• FAQ

How the Glow Effect Works

The glow is fluorescence — cake components absorb UV light and re-emit it as visible light. Two ingredients make this happen:

• Tonic water — Contains quinine, which fluoresces bright blue-white under UV light. Replace regular water with tonic water in your frosting.
• Neon food coloring — Americolor Neon series (Electric Pink, Neon Brite Blue, Neon Brite Green, Electric Orange) fluoresce vividly under UV. Regular food coloring does not glow.

You will need a UV/black light to reveal the glow. Inexpensive LED black light bulbs are available on Amazon for under $15.

What You Need

• Two 8 or 9-inch round cake pans
• Stand mixer or hand mixer
• Neon food coloring — Americolor Neon series (critical — regular colors do not glow)
• Tonic water — plain/original only, not diet
• UV / black light bulb or party light strip

The Cake

Ingredients (Vanilla Cake)

• 2 1/2 cups all-purpose flour
• 2 1/2 teaspoons baking powder
• 1/2 teaspoon salt
• 1 cup unsalted butter, softened
• 2 cups granulated sugar
• 4 large eggs
• 1 tablespoon vanilla extract
• 1 cup whole milk
• Neon gel food coloring (1 to 2 colors)

Instructions

1. Preheat oven to 350 degrees F. Grease and flour two 8-inch round pans.
2. Whisk flour, baking powder, and salt. Set aside.
3. Beat butter and sugar 4 to 5 minutes until pale and fluffy.
4. Add eggs one at a time, then vanilla.
5. Add flour in three additions alternating with milk. Mix until just combined.
6. Divide batter and tint each portion with a different neon color. Use generous amounts.
7. Layer or marble colors in pans. Bake 28 to 32 minutes until a toothpick comes out clean.

The Glowing Buttercream Frosting

Ingredients

• 2 cups (4 sticks) unsalted butter, softened
• 6 to 7 cups powdered sugar, sifted
• 4 to 6 tablespoons tonic water
• 1 teaspoon vanilla extract
• Pinch of salt
• Neon food coloring

Instructions

1. Beat butter on high for 3 minutes until pale and fluffy.
2. Add powdered sugar 1 cup at a time on low speed.
3. Add tonic water 1 tablespoon at a time to reach spreadable consistency.
4. Add vanilla and salt. Mix well.
5. Divide into bowls and tint with neon colors. Leave one portion white — tonic water alone creates a blue-white UV glow.

Decorating for Maximum Glow

• Ombre neon layers — Frost the outside in bands of neon colors that blend into each other. Each band glows a different color under UV.
• Neon drip — Make a neon ganache (white chocolate + neon food coloring + tonic water) and drip it down the sides over white frosting.
• Splatter art — Dip a stiff brush in thinned neon food coloring and flick it at the frosted cake for a galaxy splatter effect.
• Neon rosettes — Pipe neon star rosettes or swirls over the white base coat. Each rosette glows its own color under the black light.

Tips

• Test your UV light beforehand — LED UV strips and dedicated party black lights work far better than novelty mini-bulbs
• Dim the room — The glow effect requires near-darkness to look dramatic. Set up UV lighting before guests arrive.
• Original tonic water only — Diet tonic has less quinine and glows less brightly
• More neon coloring = more glow — Be generous, these need more color than standard gel food colors
• White frosting glows best — A white base coat fluoresces clearest blue-white under UV

FAQ

Is a glow in the dark cake safe to eat?

Yes — tonic water and food-grade neon food coloring are both safe and FDA-approved for consumption. The UV light is external and does not affect the food.

Does it glow without a black light?

No. This is fluorescence, not phosphorescence. The cake only glows when a UV light shines on it. Without UV, it looks like a brightly colored neon cake — still fun, just not glowing.

What neon food coloring brand works best?

Americolor Neon series is the most recommended for UV reactivity. Chefmaster Neon is a close second. Standard grocery store food coloring will not fluoresce under UV.

Can I make this without tonic water?

Yes — neon food coloring alone will fluoresce under UV. Tonic water adds additional glow to the white frosting areas, making the effect more dramatic, but it is not required.