OT: white LEDs

Keith keithvz at verizon.net
Mon Feb 22 22:17:04 CST 2010


Curt @ Atari Museum wrote:
> That is true, they last longer and would save a heck of a lot of 
> maintenance

Right.  Instead of a single bulb, there are many smaller LEDs, and the 
biggest benefit is that they all don't fail at the same time.  This 
makes them much safer.  I don't know what the MTBF is on those things 
but I've seen a couple burned out in some of the lights around here.

>... I always thought like 10-15 years ago "when will they 
> make traffic lights and street lights smart enough that when they fail, 
> a signal is sent so that someone will come and fix them..."

I used to talk to the technical people in charge of these types of 
projects in city/county/etc government.  This isn't all that new, 
either.  They've used RS422 and RS485 and run copper twisted pair 
between the lights, and then home run single mode fiber back to the 
centralized building.

I got involved w/ them because they wanted to "network"-ify these old 
light controllers.  The newer controllers are ethernet-based.  I gave 
them a solution to transmit serial over tcp/ip, and then use small 
network switches that would use the legacy single mode.  The advantage 
there was that they'd now have ethernet in these street-side boxes which 
made things like network-based cameras easy to connect.

These switches had two single mode fiber ports (or multimode for shorter 
distances) and then around 6-8 copper 10/100 ports.  What made them 
great for these types of projects is that they were industrial 
temperature rated. They were -50C to +100C rated, and designed for long 
term use at -40C to +75C.

At the central location, they had big monitoring screens where they 
could see the status of every light, and have live video of the 
intersections.  Pretty neat.

>   I would think that with their new low power lights there 
> would then come the eventual Wifi status transmitter that would send out 
> a functional status of a light, traffic signal, etc that could all come 
> into a center monitoring station and know when something fails.

Yup. I designed some of these types of networks too!  Especially nice 
when they already have some of municipality wide wifi installed.

Keith




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