Rainbows everywhere

[Alps]

https://phys.org/news/2019-08-retroreflective-material-nighttime-color-changing-road.amp

The MUTCD requires devices to appear the same color by day and night. I don't see this technology changing that rule.

[hbelkins]

https://phys.org/news/2019-08-retroreflective-material-nighttime-color-changing-road.amp

The MUTCD requires devices to appear the same color by day and night. I don't see this technology changing that rule.

Depending on the angle of the prevailing light, or of the viewer's eyes, sometimes existing sheeting will briefly reflect a rainbow spectrum. I've noticed this mostly in white and yellow sheeting.

Weren't some of the old night speed limit signs designed to reflect differently in daytime (natural light) or nighttime (artificial light from headlights) conditions?

[kphoger]

↓  Here you go, HB.  Everything is on this forum somewhere!     ↓

They used the signs with the first digit having a non-reflective daytime number and a retroreflective nighttime number behind it, so your headlights would reflect the nighttime speed.

Does anyone have photos of one of these units? I remember reading in the 1971 MUTCD:

...reflectorization of the nighttime speed superimposed over the unreflectorized numerals of the daytime speed, to permit only the nighttime speed to become legible in the beam of motor-vehicle headlamps at night.

It seems to me that this setup would be troublesome at twilight and under odd conditions where a strong light source is directly behind the motorist, causing both sets of numerals to be visible.

I have no photos, unfortunately, although I do have sign design sheets:



Under twilight and extreme frontal lighting there might be problems with the night limit "ghosting" under the day limit, but I don't know that these would have been more serious than the shortcomings of other reflectorization practices then in use, such as rendering black "EXIT ONLY" against yellow on lane-drop signs in button copy.  I strongly suspect it was the NMSL rather than reflectorization voodoo that killed these day/night signs.

[hbelkins]

https://phys.org/news/2019-08-retroreflective-material-nighttime-color-changing-road.amp

The MUTCD requires devices to appear the same color by day and night. I don't see this technology changing that rule.

Depending on the angle of the prevailing light, or of the viewer's eyes, sometimes existing sheeting will briefly reflect a rainbow spectrum. I've noticed this mostly in white and yellow sheeting.

And after I posted this, I saw someone's post on Facebook that they had acquired an AZ 95 marker. The photo showed a bit of rainbow reflection. Maybe others here saw that too.

[renegade]

↓  Here you go, HB.  Everything is on this forum somewhere!     ↓

They used the signs with the first digit having a non-reflective daytime number and a retroreflective nighttime number behind it, so your headlights would reflect the nighttime speed.

Does anyone have photos of one of these units? I remember reading in the 1971 MUTCD:

...reflectorization of the nighttime speed superimposed over the unreflectorized numerals of the daytime speed, to permit only the nighttime speed to become legible in the beam of motor-vehicle headlamps at night.

It seems to me that this setup would be troublesome at twilight and under odd conditions where a strong light source is directly behind the motorist, causing both sets of numerals to be visible.

I have no photos, unfortunately, although I do have sign design sheets:



Under twilight and extreme frontal lighting there might be problems with the night limit "ghosting" under the day limit, but I don't know that these would have been more serious than the shortcomings of other reflectorization practices then in use, such as rendering black "EXIT ONLY" against yellow on lane-drop signs in button copy.  I strongly suspect it was the NMSL rather than reflectorization voodoo that killed these day/night signs.

We used to have those in Michigan.  I do not have photos of any, however.  They went away as part of the NMSL.