The Science Behind: Things that Glow in the Dark

It’s almost Halloween and time for spooky things that glow in the dark!  Have you ever visited a dark room in a haunted house where your tee shirt and teeth radiated a greenish or purplish  hue? That eery gleam is caused by a special type of light – called ultraviolet light (also known as “black light”) – that can make certain things glow in the dark!

How does ultraviolet light make things glow?

Ultraviolet light is a special kind of light that we humans can’t normally see.  Imagine the colors of light as notes on a piano — a special piano with rainbow keys. The lowest notes are red, then orange, then yellow, all the way up the keyboard to the highest, tinkliest violet notes. Now imagine that  that the rainbow keys are just a tiny section of a giant keyboard with a full range of notes. Those keys just past the purple ones? They’re the UV keys. They play notes, just like the purple keys, but the sound they make is too high-pitched for us to hear. It’s the same thing with UV light. However, just because we can’t see UV light doesn’t mean we can’t see what it does.

Glowing from UV light is called fluorescence. Fluorescence was named after the mineral fluroite, the first known fluorescent thing that has a bright blue color.

Fluorescence was named for the mineral fluorite, the first known fluorescent thing, that has a bright blue color.

So what happens to make a fluorescent material glow? Well, when it gets hit by ultraviolet light, the atoms in that material absorb the UV light and become excited. Think of it like how a trampoline bends to absorb the energy from your bounce. The trampoline can’t hold that energy for long, though, so it releases it by springing you upward. The same thing happens with fluorescence: the atoms release their excited energy as visible light. That’s the glow you see.

Some toothpastes have fluorescent whiteners. They’ll make your smile so bright it glows in the dark.

Humans see fluorescence best in the dark because we can’t see ultraviolet light. It’s outside the range of rainbow colors that our eyes respond to. When invisible UV light makes something fluoresce in the dark, it looks to us like that glow is coming out of nowhere. The glow still happens in daylight too, but we don’t notice it as much because of all the other daylight color we see.

Banana spots have a blue fluorescent halo because of a chemical produced during the ripening process.

Other animals (like insects, birds, and fish) notice fluorescence even in full daylight because they can see UV light. To them, UV looks like any other color in the rainbow. When a fluorescent thing turns UV light into a different color, it looks to them like if a yellow street lamp made your clothes glow purple instead yellow. Scientists think that the ability to see UV is why some of these animals evolved fluorescent markings.

Some butterflies use fluorescent markings to tell if they’re male or female.

Fluorescent objects can hide in plain sight. You only see the glow when you turn out the lights and shine a UV light on them. You might be surprised to learn what things can glow at home and out in the world around us.

Highlighters get our attention so well because of fluorescent compounds in their ink. Write something under UV to see it really shine!

To experiment more with things that Glow in the Dark, try out our crates and DIY projects:

Glow Lab

Haunted House

Glow in the Dark Slime

DIY Glowing Bouncy Egg

Fall Bucket List

I created our first Fall Bucket List with my kids many years ago… before they could even read! I had my son illustrate the activities so he could remember what they were — hence, the hieroglyphics. (My personal favorite: for “Make fall cookies”, he pointed out the squiggly line “is the smell of baking cookies coming out of the oven. You can see the cookies through the oven door.”  Obviously.)

We had fallen out of the practice of this tradition over the years, but at my older kids’ middle school this year, they each had to complete a September Goals exercise: “What would you like to get out of this year? How would you like the year to feel to you at the end? What will you set as your intention?”

It made me remember the appeal of our old Fall Bucket List. And I have to say, the idea of a bucket list (or a goals list – call it whatever you like) appeals to me these days more than ever.  I feel like the weeks, months and seasons fly by so quickly now with the busy-ness of school, activities, sports, etc. I really like the idea of trying to be more intentional with how we spend the time we have.

How do we want this season to feel? What are our intentions?

We talked about it as a family in the car on the way to school one morning (sidebar: I find the car an excellent venue for questions like these; the kids cannot physically run from the question, but also, there’s a finite limit on how long Mom can push the discussion, because they know we will get wherever we’re going pretty soon. The teen and pre-teen seem happier to engage with those boundaries set 😉.) Here are the intentions that we settled on:

Practice gratitude.
Be curious.
Get cozy.
Embrace (some) adventure.

And so with those in mind, we brainstormed our new list. There are some repeats from before (because who doesn’t love traditions?) and a few new ones to try. (Yes, you’ll notice I was able to enlist one of our fabulous designers to help me — no, my own graphic design skills have not improved on their own by 1000%. Thank you, Jessica! She even made a blank one for you!)

A few other personal favorites that didn’t make our final list this year, but I am still hoping to do:
Acorn Cap Jewels – the pictures aren’t great on our blog, but the end result is always beautiful. They make a great Thanksgiving centerpiece!
KiwiCo Pumpkin Carving – for obvious reasons 😉
No Bake Pumpkin Cookies – more obvious reasons. No Bake. Pumpkin. Cookies.
Make a Leaky Pumpkin – it’s basically a vomiting pumpkin. Kids love it.

And if you’re looking for more ideas of fall activities, there are literally hundreds of them on the DIY section of our site:

Finally, here’s a link to a blank downloadable Bucket List template if you’d like to use it.

We’re always looking for new ideas, so please share:
What’s on your family’s Fall Bucket List?

The Science Behind: Sandcastle Building

With Labor Day – and the last gasp of summer – upon us, a few of you lucky souls may find yourselves on a beach this weekend, and with that the chance for some sandcastle building. I’m here to help you leverage that opportunity to wow your children with your skills and knowledge.

We all probably have memories of building sandcastles as kids, whether it was at a lake, a beach or just in a sandbox. I know for me, it went something like this: fill up a plastic cup with wet sand, let it sit for a minute, then flip the cup quickly onto the beach and then as carefully as I could, remove the cup. And usually, watch my “castle” crumble into more like a mound.

But my mind was opened to a new world of possibilities when, at a family reunion I attended earlier this summer, one of my relatives found a professional sandcastle builder to do a session with us. (I know – WHO KNEW there was such a thing??)

Janel, our Sandcastle Instructor, explained that the key to a successful – and sturdy – sandcastle is all in the SCIENCE!

The science behind sandcastle building has to do with the interaction between water and sand, and with a special force called “surface tension.” (Yes, pull that word out to impress your children.) In case you need a refresher from your high school physics class, surface tension is the force that causes water molecules to be attracted to one another. Think about what happens when you fill a glass of water to the VERY VERY TOP – you can see a domed effect where the water molecules are holding together. That’s surface tension in action.

Surface tension is what gives wet sand its strength for great sandcastle building. The water molecules coat the grains of sand and hold them together, forming water-drop bridges in the gaps between the grains. Too little water, and surface tension can’t hold the sand grains together. Too much water, and the water turns into a lubricant and your sand collapses and flows with the water, making a mushy mess. 

We learned that the magic ratio of sand to water is about 8:1 – that is, 8 parts sand to 1 part water. The other key is making sure EVERY GRAIN of sand is coated with water to maximize the number and strength of those water-drop bridges holding the sand together. (See tips on how to do that in our Technique Tips below.)

Now that you know the science behind surface tension and sandcastles, here are some tips to build the best ones!

You don’t need any fancy equipment to make a fancy sandcastle. Everything you need can likely be found in your kitchen, garage or local hardware store.

  • A long-handled, lightweight shovel: a long-handled shovel with a small scoop. The sand-sculpture task that feels the most like work is filling up the bucket with sand! A little garden spade is better than nothing.
  • A bucket or two: we used two 5-gallon buckets – one with the bottom cut off for forming the main castle (which made it much easier to mix the water and sand in, and then just lift it off) and one filled with water to add to sand for all the additions to our main structure. Of course, buckets of any size will do! Smaller buckets won’t be as heavy, so don’t worry about cutting the bottoms off.
  • Plastic molds: Use plastic food containers to make towers and building blocks. 
  • Carving tools Look in your kitchen for smoothing and shaping tools: for basic shaping, plastic knives, paint scrapers and trowels. A pastry knife or small spatula work well for detail work. Melon ballers (finally! A use for that!) or just a tablespoon work great for scooping out round windows.
  • Finishing tools: A soft-bristled paintbrush is handy for smoothing surfaces. A paper straw works well for blowing loose sand out of detailed carving.

These are tips we learned for building a sturdy base for your sandcastle.

  • Fill your building bucket with sand: Again, we used a bottomless 5 gallon bucket for this, but any size will do. To get the right ratio, fill your bucket about 90% full with sand.
  • Mix up your sand: Pour water into the building bucket where you put your sand – and fill it right up to the top. Then reach in with your hands and really mix and mix and mix to get all the sand particles in the entire bucket all coated with water. Depending on the size of your bucket, this might be a whole-arm activity. (Fun fact: this is what cement mixers do!)
  • Compact wet sand:  Packing sand strengthens and tightens the little water bridges that hold the grains together. Tap the sides of your bucket with your fists or your feet until the sand on top looks compact and almost dry. Then carefully lift off your bucket – ta da! You’ve got a clean slate sandcastle base!
  • Carve, build, decorate: Use your finishing tools – and your imagination! – to create the sandcastle structure of your dreams.

Once you have a sturdy base, you can make your own sand-dragons and sand-boats, and create beachside castles with watery moats. Use cups and old pots and pans and cookie cutters and whatever else you can find to mold interesting shapes. Keep a bucket of water close by to keep your building material sticky. Just watch out for sneaky waves (or little brothers) that can bring the whole thing tumbling down.

And though summer may be officially ending this weekend, you can bust out your sandcastle science facts to impress kids in the sandbox anytime!

Introducing Our Newest Arrival: Panda Crate!

We are thrilled to announce the launch of Panda Crateour newest line for babies and toddlers

Panda Crate was developed especially for little ones (aged 0–24 months), grounded in the science of early childhood development, and made helpful, practical, and convenient for parents. We worked closely with researchers at Seattle Children’s Hospital to ensure that all the products and information delivered in each crate are perfectly suited for your child’s developing brain

The products and information included in each Panda Crate are developed and tested to be developmentally appropriate for specific age ranges, so you’ll always get just the right crate at the right time. In fact, the Panda Crate line is broken up into five separate age bands:

    • Birth-2 months
    • 3-6 months
    • 7-12 months
    • 13-18 months
    • 19-24 months

We know first hand that the first months (and years) of your child’s life can be often busy, sometimes confusing, and seemingly never-endingly sleep deprived. We’re here to help parents feel more confident in answering all those questions around “What’s best for my baby? Is this normal? What should I be doing with her now??” And we will always do it in a way that is easy (we distill all the research for you), convenient (all the products and info are delivered to your door) and fun (because, goodness knows, parenting is already enough work)! 

The bottom line: Panda Crate allows you to focus on bonding with your baby while we take the guesswork out of what’s research backed and developmentally appropriate

If you’re familiar with our other subscription lines, you will notice one difference with Panda Crate: these deliveries will arrive at your home every other month instead of monthly. The contents of the crate, however, will be roughly double that in a monthly crate. We’ve made this change to allow us to group together more toys and materials for parents to use across a two-month stage — to better support the rapid pace of babies’ and toddlers’ development and the wide spectrum of timing along which individual children grow.

With the launch of Panda Crate, KiwiCo now has the perfect solution for any kid — or kid at heart — ages 0 to 104! Check out Panda Crate and all the rest of our lines at

Cheers from our family to yours,

Sandra – CEO, Founder, Mommy of 3

We’re On Our Way to Singapore! STEM Boxes for Kids Available

We’re delighted to announce that KiwiCo is now shipping STEM boxes for kids to Singapore!

Our projects are seriously fun, and inspire kids to become creative problem solvers. Every STEM and art box is built with care, tested for over 1,000 hours with age-appropriate options for ages 0-104. Crates are delivered monthly, and you can pause or cancel anytime!

Astronaut STEM box for kids from KiwiCo

KiwiCo Singapore STEM & Art Boxes

Panda Crate (0-24 months) – Bonding & Early Development

Koala Crate (Ages 2-4) – Learning Through Play

Kiwi Crate (Ages 5-8) – Creative Learning

Atlas Crate (Ages 6-11) – Geography & Culture

Doodle Crate (Ages 9-16+) – Crafting & Arts

Tinker Crate (Ages 9-16+) – Science & Engineering

Maker Crate (Ages 14-104) – Crafting & Arts

Eureka Crate (Ages 14-104) – Science & Engineering

STEM & Art Box Shipping Rates

International shipping rates for Singapore start at $4.95 USD. A full list of countries we ship to can be found here. When you begin a new KiwiCo subscription, we’ll ship the first box within 1-2 business.

Want to hear what our awesome customers are saying about us? Browse through over 19,000 KiwiCo reviews! We are so pleased to welcome Singapore to our growing KiwiCo community!