Photo by courtesy of UlmanDesign

Here you can find answers for most common questions about luminescent pigments.

1. What is the luminescent pigment?

Luminescent pigment is often called glow in the dark powder or phosphor. It's used to give products ability to self-glow in the dark after exposing to natural or artificial light. Pigments unlike dyes do not dissolve in medium but makes suspension – less or more stable depends on pigment's particle size and medium viscosity.

Luminescent pigments in contrast to UV pigments not need constant light to work – after charging this product can self-glow up to 12 hours or even longer. Charging and glowing cycle can be repeated countlessly without significant reduction of luminescence properties.

All glow in the dark pigments in our offer are based on strontium aluminate – this is the latest generation of phosphors that has about 10 times better glowing power compared to older generation based on sulphures.

2. What is the lifespan of luminescent pigments?

Strontium aluminate is very stable compound – producer declares lifespan over 15 years. Even after 15 years pigment will still glow but it's glowing power will reduce to level where it can't be treated as a new product. Still this reduction will be not very significant.

Of course a lot depends on way that we use glow in the dark powder – for example if we mix not waterproof pigment with a bad quality lacquer and after few years due to lacquer damage pigment will be vulnerabled to moisture - lifespan will be reduced.

3. How long it takes to fully charge glow in the dark pigment?

   In good light conditions (illuminant D65 which is similar to bright, sunny day) pure pigment needs 15 minutes to fully charge. This time may be elongated due to two factors:

   - properties of base that we used to mix with pigment. For example if base isn't fully transparent or luminescent pigment particles will be covered by thick layer of base, time of fully charging will extend.

   - even more important factor is a place where pigment will be used and type of light source. Luminescent pigment placed in deep shadow or charged with weak artificial light source will in fact never fully charge.

   There is a glow in the dark pigment S-ZZS380 which is special type of phosphor that has reduced charging time. To be fully charged it only needs about 5-7 minutes of exposition to good light source. This pigment will be perfect for all applications where access to light is only for a moment – even if it not fully charge surely charging level will be better than regular pigment.

4. How long luminescent pigment glows in the dark?

If we were unfair or unreliable seller we will write here that pigment will glow for 12 hours and end this paragraph at this point. But this is only a half of truth. Some luminescent pigments in our offer glows even longer than 12 hours but don't deceive ourselfs – after 6-8 hours glowing strength will be really weak and this effect will be visible only in decent darkness.

After ten minutes since light source is moved out phosphors glows with about 10 times weaker power than during first seconds. This is a feature of this technology – different luminescent pigments from different sources could glow better or worse but overall tendency is the same. After this first 10 minutes of glowing decreasing of luminescence over time isn't as great as at beginning. Depending on exact pigment type impressive effect could be visible during first 1-3 hours of glowing (the best are yellow-green and aqua-blue pigments and on the other side of scale pink-red and pink pigments have the weakest glowing). It's important to keep in mind that glow in the dark powders works by their surface – it means that big part of wall painted with luminescent pigment will give us interesting effect even after 8 hours or more.

Maybe the most important factor in this matter is surroundings of luminescent product. The deeper darkness level the better glowing will be seen. On the other hand if there will be some light sources nearby to our product, glowing phenomenon will be less visible or even not visible at all – this may be compared to making phone call during a rock concert. So all in all the best option for luminescent pigment is a place where it can get a lot of light during charging and complete darkness during glowing cycle. The further we move from those conditions the weaker glowing effect will be visible.

5. Does temperature affect luminescence of the pigment?

   Yes. In higher temperatures luminescent pigments glows stronger but in shorter time period – and in low temperatures glowing is weaker but more stable in time. This effect isn't important indoors where temperature is usually stable but in case of using photoluminescent pigment outdoor we should remember about it.
   
   

6. Are glow in the dark pigments harmful?

   Luminescent pigments based on strontium aluminate are not toxic, flammable nor radioactive.. It's worth to mentioning that one of the norms that our pigments fulfil is EN 71-3 - this norm regulate amount of heavy metals in toys which may be swallowed by small kids.

   However this pigment are in form of small, hard and rough crystals. Such particles may irritate skin, eyes and airways. Hence during work with raw pigments it's suggested to avoid making redundant dust and using dust mask, protection gloves and glasses.

7. What is mixing ratio of luminescent pigments and medium?

   There is no one, universal mixing ratio. A lot depends on medium that we will use and choosen technology. In case of plastics pigment addition vary from 5% up to 30% by mass. For resins (especially when we merge resin with wood) this ratio is 20-30%, in case of making glow in the dark paint 15-25% (more when we use bigger particle pigment and less in case of fine particles). Screen printing may need up to 50% addition of glow in the dark pigment.  Everytime when we start new project it's wise to make some test first to determine best addition of glow pigment. Beside of that you can always write to us - we have wide experience in this matter and we are always eager to help our customers.

8. What kind of mediums may be used with luminescent pigments?

   First of all as transparent as it's possible. Medium can be coloured with some additional dye but you should remember that less transparent medium you will use - less light will charge pigment and less glowing will be visible by us. So small addition of dye will not harm glowing - as long as medium will allow us to see through. You can always mix luminescent pigment with oryginally coloured mediums (like white wall paint) but this is always a lottery - you never know what dye/pigment producer used and how this substances will affect glowing power. Usually the darker colour of paint is the more it affect glowing - but sometimes even white paint can harm glowing a lot.

   If we use not waterproof pigments (which is most popular option) choosen medium must not contain water and protect pigment particles from water and moisture.

   Last important thing - we should avoid any lacquers with UV filters - such filters may significantly reduce or even block charging of glow in the dark pigment.

9. How to store glow in the dark pigments?

   There is the same rules as in case of other common chemical substances - dark and dry place, out of reach of children. Temperature should be from -50C up to 60C. Containers should be tightly closed to protect pigment from moisture.

10. Can I grind glow in the dark pigment to get more fine particle size?

    This is not a good idea because of few reasons:

    - Strontium aluminate has relatively high hardness 7,6 in Moh's, hence there is risk that during milling we will contaminate glow pigment and also harm milling equipment.

    - During milling pigment will contact with moisture which will damage it. Also waterproof pigments will lose their protection layer.

    - Smaller particle size means weaker glowing.

    So it's suggested to think about the best particle size of luminescent pigment for uour application before purchase. In case of any doubts we are always here to help you.

11. Which glow in the dark pigment is the best for resin?

    Most popular choices of our customers in this case are luminescent pigments L-ZZ660 (yellows-green) and L-JN475 (aqua-blue). Reasons are strong glowing power, UV resistance and relatively small price. Quite big particle size (100-120um = 0,1-0,12mm) isn't a problem in this case  because pigment will be covered my resin layer. But in case of small details (like glow in the dark resin jewelry) or thin layers (under 2mm) it's better to take smaller particle size pigments (0,03mm) like S-ZZ300 and S-JN260.

    Interesting choice may be M-ZZ620 and XL-ZZ1150. First has small particles combined with high glowing power - second one has very large particle (0,22-0,28mm) but also strongest glowing power in our offer.

12. How to make glow in the dark paint and which luminescent pigment choose?

    The first step to make luminescent paint is choosing proper medium. If our choice will be water based medium (for example water based acrylic emulsion) then we must take waterproof luminescent pigments. Such pigments are more expensive and there is limited selection of them. So if it's possible it's always better to use solvent based medium (for example nitrocellulose lacquer or epoxy resin).

    Now we should decide which particle size of pigment will work well in our application. If painted object will be watched from afar then we can use larger particles (pigment code starting with "L" letter) which has better glowing power. For objects that will be close to observer eye we should take fine particle pigments ("S" and "M" first letter of pigment code). Such pigments will give smooth and even surface. Also painting with fine particle pigments is easier.

    Next step is determining where painted object will be located. Proper pigments for outdoor usage are colours yellow-green, aqua-blue and sky-blue. In case of indoor usage all colours of pigments can be used. Find more information on how to choose the right luminescent pigments.

    Yellow-green, aqua-blue and sky-blue pigments has whitish colour during the day. You can add some dye to medium to make daytime colour of paint similar to glowing colour. Please remember that addition of dye should as small as possible - it's important to keep transparency of medium. Less light luminescent pigment get - weaker glowing will be in result.

    In case of pigments available in few particle size you may consider mixing 2 pigments. For example:

    - 20% of M-ZZ620 luminescent pigment and 80% of L-ZZ660. 20% addition of smaller particle size pigment fills all empty spaces between larger particles of pigment. Thanks to it surface is better covered by glow in the dark pigment and in result we get better glowing.

    - 20% of S-ZZ300 luminescent pigment and 80% of L-ZZ660 pigment. It's the same scheme as above but effect will be weaker because S-ZZ300 pigment is weaker then M-ZZ620. But it's also cheaper.

    - 20% of XL-ZZ1150 pigment and 80% of L-ZZ660. In this option we enhance glowing power by adding strong glowing XL-ZZ1150 pigment. It will be good option especially in long time period glowing (like 4-8 hours) but big particle size of XL-ZZ1150 pigment may be problematic in some applications and glowing may be heterogeneous when seen from close distance.

    - 20% of XL-ZZ1150, 20% of M-ZZ620 and 60% of L-ZZ660 pigment. Here we combine better surface coverage with long time glowing.

    This is only examples and you can use other proportions.

    To make glow in the dark paint 15-25% of luminescent pigment and 75-85% of medium is needed. Components should be well mixed to get even suspension. Bigger particle of pigment - less stable suspension - so we will have to mix paint more often.