Custom Traffic Signs
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A quick history of sign reflectivity

Wayfinding street signs
Wayfinding signs like this one can also provide crucial information – as anyone showing up after sunset will find.
If you ask someone what they identify with the word "sign," chances are good they'll say something like "stop," "detour" or "yield." Traffic signs are among the most ubiquitous of behavioral cues that we run into each day, but there's more variety among traffic signs than most people recognize, and the technical expertise that goes into each traffic sign is truly a marvel.

At first, signs often had to have lanterns lit next to them to ensure that drivers would see them. Later, reflective glass beads were taped onto signs, but this approach had limited success and outside a few specialist applications, was discontinued by the end of World War II – the beads couldn't stand up to bad weather, and the quality of reflectivity degraded almost immediately. 3M were and are still pioneers in the field of reflectivity,, though, and by 1939 they'd developed a sturdier variety, so they patented Scotchlite reflective sheeting, which is still in widespread use.

Over the years, 3M also developed prismatic sheeting that's even more reflective than their glass beads. Most of their High Intensity and all Diamond Grade varieties use prisms in a honeycomb pattern that bounces light directly back to the source. Engineer Grade diffuses the light slightly, but Diamond Grade signs are so bright that they may not be appropriate in all circumstances – they can be difficult for some people to see at night if they're lit at certain angles.

3M's inks are also highly unusual in that they're transparent – they allow light to bounce through the prisms behind them and then back out again. (At night, opaque or screen-printed inks painted onto reflective film of any sort simply looks like blacked out areas.)

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