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#### What is Fluorescence/Phosphorescence?

I won't bore you with math and I'm going to oversimplify the science a bit in order to explain how this works, but this should at least convey the essentials as they relate to Lego.

Fluorescence is when an object absorbs light of one kind and immediately emits a different kind. The most well-known example of this is in "neon" colors, which respond to invisible ultraviolet light by emitting visible light. Put simply, when you shine a blacklight (a light designed to emit UV) on a fluorescent object, it glows. When you stop shining UV light on it, it stops glowing immediately.

Phosphorescence is related to fluorescence, but works on a slower time scale. It is found all over nature, but the example that comes to mind for most people is that of "glow in the dark" objects, which "charge" like a battery by absorbing UV light (whether from the sun or a blacklight) and then continue to glow at a lower intensity for varying amounts of time after the UV stimulation stops.

There are many different TLC (The Lego Company) and Brickarms colors which are fluorescent, and a small handful which are phosphorescent. To simplify things I'm going to refer to fluorescent colors as "neon" and phosphorescent colors as "GITD" (for "glow in the dark").

Lego Colors
Trans-Neon Orange: glows a very bright orange color - different from Trans-Orange, which does NOT glow
Trans-Neon Yellow: glows a sickly greenish-yellow
Trans-Neon Green: glows a very bright yellowish-green; is so bright that it tends to wash out when photographed
Trans-Bright Green: glows a moderately bright apple-green
Glow In Dark Opaque: weakly phosphorescent; glows a sickly green
Glow In Dark Trans: moderately phosphorescent; glows a sickly translucent green

Brickarms Colors
Trans-Green: production color--glows a very bright greenish-yellow; comparable to (but slightly paler than) TLC Trans-Neon Green and tends to wash out even more in photographs under UV
Trans-Orange: production color--similar to TLC Trans-Orange in visible light; glows a moderately bright green with orange tints under UV and shows surface detail well--the thinner the ABS, the more bright and green
Trans-Apple Green: non-production color--comparable to TLC Trans-Bright Green under visible light; glows similarly to BA Trans-Green under UV but not as brightly
Neon Bronze: non-production color--iridescent semi-translucent bronze under visible light; glows a weak green under UV and shows surface detail well
Neon Metallic Green (Jade): non-production color--vivid metallic/pearlized green under visible light; glows moderately bright green under UV and shows surface detail well
Glow In The Dark Green: phosphorescent non-production color--pale GITD green under visible light; glows moderately bright green under UV, glow continues after exposure to UV and fades over a period of time

Will has also injected test runs of many different glow-in-the-dark materials of one color and intensity or another. These are typically rare and hard to find, and the quality of the glow varies widely.
Thanks for this, might come in handy.
Thanks for this Catsy. This will help me a lot. I do have a question though, does Brickarms Trans Blue glow under blacklight?
It doesn't truly fluoresce, but what you will see with trans-blue, trans-clear and a few similar colors is that they will refract the visible wavelengths of the blacklight the way they would any other light source, making them appear to have an extremely faint glow from certain angles and light levels.

Blacklights emit a dim purplish glow which does provide a small amount of visible illumination. Sometimes this is helpful because it provides a subtle light level so that the shot isn't in complete darkness, thus obviating the need for another light source--but you also have to be mindful of it to avoid purple reflections and tints if those are undesirable. Sometimes it can be helpful to adjust the color balance and channels in the final shot.
im thinking about entering... when was the final cutoff date again?

Rule #1.
Thank you, Catsy.
Have you tried the tlc color trans dark green under a blacklight?
there was an old trans pink-ish color used for bionicle heads, it glows i believe.
What about trans red and blue? Do they not glow?