lux and street signs...an interesting question

I'm sure someone somewhere knows this...it is probably some sort of guideline that the sign manufacturers must follow.
Maybe a DOT code of some sort.

How many lux is required to "reflect" a street sign?

I ask this, because I know of a 3/4 mile stretch of road near me, that many of my lights will illuminate the sign at the 3/4 mile mark.

So, I wonder, that's almost 4,000 feet. (1200 meters)
How many lux is at the 4,000' mark do you think?

Limey Johnson said:

I'm sure someone somewhere knows this...it is probably some sort of guideline that the sign manufacturers must follow.
Maybe a DOT code of some sort.

How many lux is required to "reflect" a street sign?

I ask this, because I know of a 3/4 mile stretch of road near me, that many of my lights will illuminate the sign at the 3/4 mile mark.

So, I wonder, that's almost 4,000 feet. (1200 meters)
How many lux is at the 4,000' mark do you think?

Click to expand...

Almost nothing...When I shoot pics down a transmission tower right of way...I'll do a dark control shot...which will look black, and one with the flash...and with the flash, reflectors on the towers light up all the way down the line as far as the eye can see. I'd say with a reflector, its almost like you are shining your light back at yourself...so if your light is visible at that range, you'll probably see your reflection, etc.

For perspective, its a point and shoot camera with a flash that has a ~ 20' range or so...as far as for flash pictures....and its over a mile straight away down the line of reflectors.

I get the same thing with even pocket lights...reflectors throw the light back really well.

Almost no lux required.

The signs are Retroreflectors.
Most of the light hitting a reflective sign will be sent back in the exact direction it came from, and relatively little is scattered or absorbed.

With a normal white object the light would be scattered evenly in all directions.
The sign, however, catches the light and virtually focuses it back to your flashlight.
The further away (sideways) from the source of light (your flashlight) you are, the less bright the sign will appear.