Charles Fraser-Smith had a problem.  He had a lot of problems actually;  he was the chief gadgeteer for the British espionage agency MI6 during WWII.  He was responsible for all the gear that agents would need on the Continent, from the right styles of clothes and shoes and cigarettes, to maps hidden in buttons, to cameras and radios that could be concealed anywhere.  Ian Fleming happened to know him, and based the character of Q in the James Bond books upon him.

His problem was that British planes couldn’t find the French fields that they needed to land on to supply the Resistance. With German soldiers and planes everywhere you could hardly set up bright landing lights.   You couldn’t even give them powerful flashlights for fear of being stopped and exposed.   He tried making flashlights that looked like innocuous other objects:

But the batteries failed when needed.  He needed something bright and reliable and so came upon this:

Plastic balls painted on the inside with glowing radium paint.  Just toss them on the edges of a field before the plane was due to land, and they would stand out against the dark ground of the countryside.  Then stash them in the woods afterwards in an opaque bag for next time, since they’ll still be shining. Radium was in regular use for glow-in-the-dark watch and clock faces, so there were supplies of it even in wartime.

Click for link to exhibit at the Tangmere Museum

He describes this in his memoir The Secret War of Charles Fraser-Smith (1981), but doesn’t talk about how well it worked.  It’s possible that it was used only once or perhaps not at all.

Maybe that’s because it was a really terrible idea.  Radium is poisonous even in microgram quantities, and these would need a lot of it.   Even so they wouldn’t be all that bright.  Radium paint glows by phosphorescence, which isn’t that efficient.  The phosphors do get damaged by the radium’s alpha particles over time, so present-day antique radium clocks no longer glow.  Also, the Germans had Geiger counters even then (they used them to find their own radioactive land mines), so if the radium ever got on someone’s hands they could be discovered.   Fraser-Smith had plenty of ingenious ideas, and his book is a really fun read, but this wasn’t one of them.

The US military actually did make use of glowing radium disks for marking people, ship decks, and bridges:

Radium Personnel Markers – click for good article.  Note the Poison marking

These had a belt clip so that you could wear them right next to the family jewels.  They switched to Strontium-90 in the 1950s because it was cheaper and lasted longer.  This was in use right up into the 1960s, incredibly.  Oak Ridge Associated Universities has a big collection of radioactivity-related items, and discusses these here.

The other big use of radioactive lighting was for uncrewed lighthouses in remote places.  These used the heat from radioactive decay to power thermocouples to generate electricity, a Radioisotope Thermoelectric Generator.  They generally used strontium-90 and produced 10 to 100 watts for about 10 years. The US and UK built a few, but the big user was the USSR.   The Russian-Norwegian environmental watchdog Bellona estimates that there were 1000 abandoned units like this scattered around Russia:

Looted Soviet RTGs.  Note the cooling fins around the hot core

Records of them were lost when the USSR fell.  They’ve gotten looted for scrap metal, and people have come into ERs with radiation burns.  Tens of millions have been spent on finding them and disposing of them properly.  They’ve been largely replaced by systems with solar panels and batteries, but Rosatom has announced that they’ve come up with a new scheme based on nickel-63.  This one will be completely safe, honest.

This highlights the real issue with this whole concept – you only get light out of them for a few years and then they become dangerous radioactive waste.   The more broadly they get used, as on bridge markers or beacons, the more likely they are to be mishandled.  50s SF stories were full of eternal atomic light bulbs, but the reality is much nastier.  The 20th century put so much radioactivity into the ecosphere that it’s a mark of the Anthropocene, and here was another example.