Glow In The Dark Pieces Fade?

TyresOFlaherty

So, I recently unearthed my childhood collection of Lego, and found my old buddy Majisto in there with his magic wand and my ghost (from 6081), and I noticed that these barely hold a glow anymore, when compared to my Spectre, who glows for a good 20-30 seconds, while the magic wand and ghost seem to fade before 5 seconds.

I assume this is pretty common since those pieces are so much older, just wanted to see if anyone else has noticed the same thing. 

Fauch

my spectre glows for much more than 30s. I don't know for how long, but I would guess at least half a hour.

madforLEGO

TyresOFlaherty said:

So, I recently unearthed my childhood collection of Lego, and found my old buddy Majisto in there with his magic wand and my ghost (from 6081), and I noticed that these barely hold a glow anymore, when compared to my Spectre, who glows for a good 20-30 seconds, while the magic wand and ghost seem to fade before 5 seconds.

I assume this is pretty common since those pieces are so much older, just wanted to see if anyone else has noticed the same thing. 

I always thought that the more the glow in the dark item is exposed to light it wears down the effectiveness (but someone with a scientific background would need to confirm) as for the effectiveness of recent glow in the dark figures I have a baggie of LEGO ghosts that glow for a while, and sometimes freaks me out if I forget where they are in my apt and my light turns off.

TyresOFlaherty

@Fauch, I'm sure the glow on my Spectre lasts longer than 30 seconds, I just feel like the falloff is way quick on the ghost/want. After taking the light source away, the glow on those lasts a few seconds at best, then it's a very very slight glow for a while. 

@madforLEGO I'm sure you're right about the effectiveness of the glow material wearing down after time, I am looking for a confirmation from someone who knows way more than I do, as well.

AllBrick

Yep, pretty sure GITD stuff gets weaker over time, and leaving stuff in the light makes this happen quicker.

From a Google search....
In this special case of phosphorescence, the absorbed light energy transitions to a higher energy state, usually to something called a “triplet state”.  Because of this, the energy can get trapped in this triplet state and will take time to return to the lower energy state.  In certain phosphorescent compounds the lifetime of the triplets can last minutes or even hours, allowing these compounds to effectively store light energy in the form of slowly degrading excited electron states.  So basically, the longer the triplet lifetime, the longer it will glow, and vice-verse.

MattsWhat

^assuming that is what is used to make LEGO glow, then it should glow exactly the same forever - the excited electron doesn't go anywhere or do anything else.  They must put the phosporescent chemical into the plastic, I would imagine therefore if the plastic degrades over time then maybe some could escape (at least in theory) or become 'damaged' but this is unlikely IMO.  It's more likely they have changed the phosphorescent chemical since the original ghost to produce a longer glow (based on the stability stated above).
For the purposes of your experiment, it is also worth noting that it would take different phosphorescent chemicals different amounts of time to 'charge up' - this is why they can glow well into the night if they have been in the sun all day.  Let them sit in the light for a long time and then observe the length of glow to check, it will last much longer.  It may be the light you are using promotes electrons in one chemical and doesn't in the other too - use sunlight to get the best results as it has a fuller spectrum.
Also, it is possible that the older ghost has a more scratched up/dirty/faded surface.  This will reduce the amount of light penetrating into the plastic and reaching the phosphorescent chemical - reducing the glow maybe.

TyresOFlaherty

@MattsWhatThat's a good idea, I usually charge them with the light from my phone, which probably has a smaller spectrum than sunlight. Since we're still in the winter months, there's usually not much light left when I get home from work.

Tkatt

I can't find it now, but I'm sure I've read somewhere that freezing Glow in the dark parts before charging them up will get them to glow brighter longer.

CCC

Tkatt said:

I can't find it now, but I'm sure I've read somewhere that freezing Glow in the dark parts before charging them up will get them to glow brighter longer.

That's for glow sticks. It doesn't make them brighter for longer though, it is slightly dimmer for longer.

Tkatt

I wish I could remember where I read it. I feel like it was mentioned in the Lego instructions that came with glowing parts. Or maybe I dreamt it.

MattsWhat

^so this is true for for glow sticks as @CCC says but it makes them last longer but be dimmer - can't have both as they are just a chemical reaction.

From a science point of view it is possible that this would work for phosphorescent chemicals.  The electron promotion energy requirement will be tied to the bond lengths and stability of the compound - although I don't know how much this makes a difference.  At lower temperatures it would stabilise these conditions, which could in theory mean that the promoted states are more stable, and the emitted light is at a more consistent wavelength, and/or contained in the visible region.  This could make it appear brighter and last longer, but I fail to see how this is useful as it would only be true inside the freezer with a light source that didn't warm up the plastic.  If you took it out it would warm up and any benefit would be lost.  Not exactly the most practical solution and I can't imagine it would be a procedure that LEGO recommended.

oldtodd33

Here's a good article. At least tells us a little of what we want to know. http://science.howstuffworks.com/innovation/science-questions/question388.htm

TyresOFlaherty

@oldtodd33 Science!! Thanks!