I was wondering which Halloween candy would make the best laser, and came across reports that Jolly Ranchers are fluorescent. I got out my UV flashlight and am able to definitely confirm this is true.

The type of fluorescence varies by color, but blue raspberry has a particularly dramatic color change from deep blue to hot pink.

An unwrapped piece of jolly rancher candy with a UV flashlight illuminating it from one end. The illuminated end is hot pink, while the shadowed areas are deep blue.
Blue raspberry Jolly Rancher, illuminated with 395 nm (presumed) LED

It's interesting to note that the green Jolly Rancher actually seems to be dimmer under UV light. My guess is that it's just absorbing UV light rather than turning it into fluorescence, and it might be more fluorescent under visible light.

The grape flavor Jolly Rancher is phosphorescent, meaning that it continues to give off fluorescent light after I turn off the UV light. In other words, it's glow-in-the-dark, though the light only lasts for a second or so. To see phosphorescence I had to switch out my big 395 nm flashlight for a shorter-wavelength 365 nanometer light.

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Grape Jolly Rancher illuminated closely by a UV 365 nm penlight. It glows a violet color while the penlight is on, and once the penlight is off, it continues to glow blue for another second or so.

What's causing this fluorescence? It's probably the dyes that give the candies their bright colors. The package lists some pretty standard food dyes, Blue 1, Yellow 5, Yellow 6, and Red 40. They're all fluorescent, especially in very viscous foods (hard candy nicely fits the bill). I couldn't find out for sure which one is phosphorescent, but Red 40 glows for longer in more viscous materials, so that would be my first guess.

(It's worth pointing out that just because they fluoresce doesn't mean the dyes are necessarily harmful - plenty of natural substances also fluoresce, such as olive oil, coumarin, and vitamin B2.)

The gummy Jolly Ranchers are also fluorescent (they have the same dyes) although the effect isn't as dramatic. The granular coating of the sour gummies makes it a bit easier to see. None of them seemed to be phosphorescent. I'm not sure why, but one hypothesis is that viscosity thing. Gummies are closer to flowing liquid than hard candies are.

Under white light, the candies are yellow, green, blue-green, and red. Under UV light their sugar coating looks purplish, while the gummies glow from within. The yellow gummy looks a little more green, and the red gummy looks a lot more pink.
Four of the sour gummy Jolly Rancher flavors, illuminated with a 395 nm flashlight

On the other hand, blue raspberry airheads are really brightly fluorescent with a very satisfying blue-to-pink color change. It also has the same dyes as Jolly Ranchers. Maybe taffy format encourages fluorescence?

Left: A blue amorphous blob that is an unwrapped Airhead taffy. Right: the Airhead is now glowing magenta.
Blue raspberry flavored Airheads, illuminated with 395 nm UV flashlight
Magenta glowing version of the previous taffy candy, now carved into the capital letters PEW
I have taken the liberty of carving the airhead into the letters "PEW"

Bonus content for AI Weirdness supporters: my cat Neon photobombing the candy photoshoot. You are extremely awesome for helping me pay my blog hosting bill, and absolutely deserve to see this (or to read about this, in the extensive alt text).

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