Bay Bridge Lights - a 25 KiloPixel, two mile display

I’m very fortunate to live in the Bay Area,  with a decent view of the marvelous Bay Bridge from our house on a hill in San Francisco.  The Bay Bridge plays second fiddle to the Golden Gate bridge, but it is still an icon, connecting us with Oakland, not to mention the rest of the country.  Tonight was a very special occasion, with the launch of Bay Lights  the installation art project you’ve probably heard about.   Unfortunately, it was drizzly and overcast, so our view was limited.  But I watched the inauguration via web streaming with my family.  The telecast featured Mayor Ed Lee and serial politician Gavin Newsom.  While it was a nice event, the video streaming video quality sucked… but that’s a topic for a future post.



Artist Leo Villareal controls the Bay Lights from his laptop.  (Photo credit: Cy Musiker/KQED)

Being involved in display technology, I was naturally curious about the engineering behind Bay Lights.  The project was initiated by artist Leo Villareal , who (according to his web site) “is known internationally for his light sculptures and site-specific architectural works.”  Leo unquestionably did an amazing job at fundraising, and navigating a complex bureaucracy in order to attach 100,000 feet of cable to the bridge.  Before I forget, they still need $2 million bucks.  You can donate here.   

The overall system – over two miles long – provides and amazing showcase of geometric illuminated patterns.   The entire North side of the bridge appears to shimmer  with dynamic and unpredictable movement.  Villareal, whose office is right down the street from our house, programmed algorithms in the display drivers for the lighting sequence, which makes for an impressive site.   But I wondered about the display technology used. 

It took some digging, but I found that Bay Lights is based on LED technology from Philips Color Kinetics.  A team of engineers in Boston formed Color Kinetics in 1997, and it was acquired by Philips five years ago.  The Bay Lights project uses a product called eW Flex SLX.   125,000 white LED’s were used in the installation, grouped into 25,000 nodes, each strapped to the vertical rods serving as the suspension structure for the bridge.  The nodes measure about an inch and a quarter wide, and are spaced one foot apart.    Overall, the press reports say this covers a span of two miles wide and 500 feet high, on four towers.   Nearly 4.5 miles (24,000 feet) of LED light strips were installed.

The Color Kinetics architecture groups 50 nodes  into a string driven by one controller.  Each node is illuminated on an 8-bit (255 level) brightness through pulse width modulation.   This means that the LED is quickly switched on and off to create the perception of different light levels.  For example, a 50% duty cycle will cause the appearance of half brightness. 

 Control signalling is made over data connections on CAT 5 cable, using a proprietary protocol at 500 kbps.  The control data is processed by hubs, probably in the configuration shown here.

One of Color Kinetics proprietary technologies is the Chromastic chip, a low-cost and lower power consumption LED driver included in each node.  The Chromasitc is typically used for RGB color control of LED architectural lighting, but for the Bay Bridge it provided a convenient means for  Villareal to provide the 8-bit brightness control.

For the past month, I’ve occasionally seen tests of the lighting system in the middle of the night from the bedroom window. When I posted reports, some of my Facebook friends have questioned the environmental aspects of lighting up these zillion LED clusters, just for fun. Let’s explore this.

The Philips eW Flex SLX modules use for the bridge are emit white light at 4,200 degrees Kelvin correlated color temperature, and hit a maximum of 16.2 lumens per five-LED node. Each node consumes up to one Watt at full brightness, which means the luminous efficacy is 16.2 lm/W.

The Philips press release states that “the new LED lighting system uses 85 percent less energy than traditional lighting technologies” 

So I wondered:  what are “traditional lighting technologies” for an installation art light show??   It seems the luminous efficacy of a typical incandescent bulb is 16 lumens per watt, virtually identical toeW Flex SLX modules.  So this would NOT explain an energy cost savings of 85%.  What’s up with that? 

With 25,000 one-watt modules, the Bay Lights consumes 25 kilowatts of power a full illuminance.  The organizers say that the lights will be turned on from “dusk until 2:00am”.  Looking at sunset times, that equates to 7 hours 15 minutes per day on average, or a total of about 180 kW/hours per day.  A recent report  says that electricity costs in San Francisco are currently more than 60% higher than the national average, at 21.2 cents per kilowatt hour.  So if all these nodes were turned on, that’s over $14,000 in electrical consumption per year.  The organizers claim that power costs are $11,000 per year, so we’re in the right ball park  --- it’s doesn't seem like too much.

You may have also been wondering about total luminance flux.  With 25,000 modules at 16.2 lumens, that comes to  at total of over 400,000 lumens  -- equivilent to around 20 typical movie theater projectors.   (Except, of course, we're talking about a 10,000-foot by  500-foot irregular shaped "screen" which is emitting, not reflecting light.)

If you're interested in longevity, the Bay Lights project says they are committed to having this art installation functional for "at least" two years.  But the good news: the LED nodes are rated at about 40,000 hours, which should keep them running for 15 years, assuming dusk to 2am operations -- just over 7 hours -- each day.   I would guess that the atmospheric conditions and salt water will greatly shorten the time before something fails.

Bottom line:  this is a cool art project, but a bit expensive at $8 million capital cost.   The $11,000 per yer in electrical costs is at least particially subsidized by solar credits.  Pundits are predicting tourism benefits of nearly $100 million.   So... why not!   400,000 lumens of visual art is kind of nice, in our fair city.