How Reflective Tape Works: From the Moon to Your Bike

In July 1969, the Apollo 11 astronauts left a panel of 100 glass prisms on the Moon. Observatories still fire lasers at it today, and the light comes straight back to them. The same trick, shrunk down to tiny moulded prisms, is what makes prismatic reflective tape light up in your headlights.

Shine a torch at reflective tape and a mirror

Drag the torch left and right, or use the slider. You’re standing behind the torch, like a driver behind their headlights. Watch how much light each material sends back to you.

Torch position

Prismatic

Glass bead

Mirror

This is an illustration of how each type behaves, not measured data. Real performance depends on the product, the angle and how clean the surface is.

The trick: a corner that sends light home

A normal mirror bounces light away at the same angle it arrived, so unless you’re standing straight in front of it, the light misses you. A corner cube is different. It has three mirror faces at right angles to each other, and light that goes in bounces off each face in turn and comes out heading straight back the way it came, from almost any direction.

Bounce a beam off a corner

This shows the idea in two dimensions, with two mirrors at right angles. Change the angle of the incoming beam and see where it ends up.

Beam angle

Whatever the angle, the beam leaves parallel to the way it came in. Real corner cubes add a third face so it works in three dimensions too.

Prismatic reflective tape is covered in huge numbers of tiny corner cubes moulded into the surface. Glass bead tape works differently: millions of tiny glass beads act like lenses, focusing light onto a reflective layer behind them and sending it back towards the source. Both are retroreflective, which simply means they send light back where it came from.

Fire a laser at the Moon

There are five reflector arrays on the Moon: three left by Apollo astronauts and two carried by Soviet Lunokhod rovers, using French-built reflectors. Pick one and fire.

Time: 0.00 s

Choose a reflector, then fire.

The timing uses the Moon’s average distance of about 385,000 km. The real distance changes through the month.

A few facts about the Moon reflectors

The Apollo 11 and 14 arrays each have 100 fused silica corner cubes, each 3.8 cm across. Apollo 15’s array has 300, so it sends back the strongest signal.
By timing the laser’s round trip, scientists found the Moon is moving away from Earth by about 3.8 cm a year.
Observatories fire pulses of light only about 2 cm thick, and still aim at all five reflectors today.
The arrays are slowly getting dustier, probably from tiny meteorite impacts splashing lunar dust onto the prisms. Reflective tape is the same: keep it clean and it works best.

Try it yourself with a torch

You can see retroreflection at home or in a classroom with a torch and anything reflective, such as a bike reflector, a hi-vis vest or a piece of reflective tape.

Darken the room and stand a few metres away from the reflective item.
Hold the torch right next to your eyes and shine it at the item. It should light up brightly.
Keep pointing the torch at the item, but hold it out at arm’s length to one side. The item looks much dimmer, even though the same light is still hitting it.

That’s because a retroreflector sends light back towards wherever it came from. The closer your eyes are to the light, the more of the returning light you catch. It’s also why reflective tape lights up for a driver sitting just behind their own headlights.

Never shine a torch or a laser into anyone’s eyes.

What it means when you choose tape

Prismatic reflective tape

Uses tiny corner cubes, the same idea as the Moon arrays. It usually sends the most light back towards headlights.

About our prismatic tape

Glass bead reflective tape

Uses tiny glass beads as lenses. Not as bright head on as prismatic, but more flexible, and it often holds up better when light hits it at a wide angle.

About our glass bead tape

ECE104 conspicuity tape

Microprismatic tape, type approved to ECE 104 for HGV and trailer conspicuity marking.

About our ECE104 tape

Shiny isn’t the same as reflective. A mirror, shiny foil or a decorative holographic tape can sparkle in daylight, but they bounce light away at an angle, so at night little of it gets back to the driver. If a tape isn’t described as retroreflective, check before you buy.

Teachers, clubs and bloggers are welcome to link to this page or use it in lessons. If you’re not sure which tape suits your project, email sales@flashbacktape.co.uk.

Want to explore more? Try Bounce Back: The Reflector Challenge, Torch Hunt and UV Glow Hunt, or see everything in our Learning Centre.

Sources

About this page

This page is for general education. The torch and corner demonstrations are simplified illustrations, not measured data, and they don’t show how any specific product performs. Nothing here is advice on road safety, vehicle conspicuity marking or any other legal or compliance requirement. For that, check the relevant standard and the product’s data sheet, and make sure a product is suitable for your use before you buy or fit it.

Facts about the Moon reflectors come from the sources listed above. Flashback Tape is not affiliated with or endorsed by NASA or any other organisation mentioned on this page.