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  5. Such an amazingly clear day. I’m really missing the solar beacon.

  6. I miss the solar beacon

  7. John,
    The ones I set for 17:15 – 17:40 today all worked! Great show!
    The interface was easy to use on my PC, and the default settings now work well

    Thank you for sharing your time and experience.

  8. A while back I saw the beacon very clearly while taking a cruise under the Golden Gate bridge, so I was excited to schedule a show toward my house in Belmont. We are pretty straight south and have clear sight to the campanile.
    We didn’t see, with naked eye or telescope, the beacon at all during our scheduled times.

    On June 28 and 29, 2015, we tried various stories (0 – 3), and slightly different coordinates, but generally about
    Lat, Long: 37.522979°N, -122.283509°E
    Height: 1stories
    Date and Time: Monday, June 29, 2015 12:15 pm
    Showtype: Standard

    Air clarity was somewhat hazy, but seemed reasonable both days — could locate campi (barely) with naked eye.
    How much leadtime does the schedule need? We entered the schedule 5 to 20 minutes ahead of time.

    Fun idea. Hope we can make it work!

  9. Would love to see some photos of just where on the Campanile the mirrors are anchored. I’ve used binoculars to look for it while on campus but can’t spot it. Maybe this chap can lend a hand (or kite)…

    Meanwhile, vote to get your own Lego Camanile …

  10. Is one of the mirrors still not functioning? I tried and failed today with view from Indian Rock. Tried 1 and 3 stories
    Lat, Long: 37.892215°N, -122.273052°E
    Height: 3 stories
    Date and Time: Thursday, April 10, 2014 1:50 pm
    Showtype: Standard
    Quality: 64% (W F)

  11. I tried it from downtown Oakland, about 5 miles from the Campanile. It was a great show, very bright, in the morning. Not so good in the afternoon. I guess it works best when the sun’s behind you. It seemed to struggle with getting the sun pointing at us when the sun’s high and at a side angle. LOVE the Google maps location feature. It’s super-easy to use, as is the whole scheduling form. I scheduled from an iPhone and everything worked well, although I couldn’t figure out how the close the time selection window. It wasn’t in the way, though, so it was ok.
    What a fun art installation!!

  12. Live above SFO on a hill in Millbrae. It’s a level lot with open space behind us so we have a panoramic view. Being retired spend a great deal of time outside on the back side of the house taking in the view while working on what ever the project is. When I learned of the solar beacon I was immediately interested in scheduling a period. Coffee time in the morning on the patio or lunch time I may schedule a period. And some neighbors that don’t have the view have come over to see the beacon. I’ll try taking a picture and will forward it if successful.
    Why in your latitude longitude coordinates do you show east longitude?

  13. Tried using an iPad this afternoon to schedule a show. It couldn’t handle with the date and time popup menu; iPad demanded keyboard intervention while the web page wanted mouse action or arrow keys.

  14. Thanks! Your “light show” was a highlight of our walk in the Kensington Hills yesterday, even though we could see the light only on one tower. I am telling others about it!

    Susan Schwartz, Friends of Five Creeks

  15. Dahlia-

    Lately, the problem has been fog at the tower tops. We cannot do anything about the
    lack of sunlight. We have also been having cellular dropouts, particularly around 17:35
    for the South Tower.

    Can you describe your problems in more detail (date, time, what went wrong eg. didn’t see any light at all)
    and send them via email to our contact email address? Russian Hill should be easy Mid-day or morning.
    A bit tricky around sunset.

  16. From the ideal Russian Hill location, I attempted to request the show twice – both times inviting scientists over to see the action happen…..however….each time it failed to work. Too bad as it’s a great idea!

  17. Tuesday, July 3, 2012 10:15 “show” was five minutes late and only south tower was reflecting. Bridge top was partially foggy. But NEAT!!!

  18. The “custom” show setting allows you to turn the individual towers on or off during the 4 minute performance. You really don’t turn off the Sun, it just points the beam away from you for a short (4 second) duration. There are 32 time slots, run twice. A check in the slot means the beam will point at you, unchecked means it points away (just a few degrees away). You can arrange the on-offs differently for the two towers. You could make a Morse coded message, but you would have to define a short and long pulse, so the message would contain only a few characters at best. We added this feature to make the show a bit more dynamic. However, some people prefer the static beam with the atmospheric scintillation (twinkling) providing all the action. Try it and let us know what you think.

  19. Can you explain how the custom personal viewing works? Can you do messages using morse code (ex. Happy Birthday Joe)? Also, could you explain how the time slot under custom in the scheduler works?


  20. Nice. Now give us back our bridge.

  21. The scheduler now displays the latitude and longitude of the point the cursor is pointing at. You still cannot enter (lat,long) coordinates, as I don’t believe many people will want to do that, but you can position the cursor by referring to them. You don’t have to be too accurate in setting the coordinates either; to the nearest 0.0001deg is OK for most purposes.

  22. Ray Mengel’s photo of Solar Beacon from Mt. Diablo can be found in the Gallery:

  23. I could see the heliostats as they were beamed to the summit of Mt. Diablo. I could see the heliostats quite clearly, from my location on the summit of Mt. Diablo.

  24. For mariners, it’d be great if it were possible to schedule position by inputting latitude and longitude. The google map doesn’t show maritime marks. For example, if I wanted to schedule a show near Blossom Rock, a navigational mark between San Francisco and Alcatraz, I have to guess where it is.

    I wasn’t able to sail to where I’d scheduled the beacon today. I’m hoping for better luck next week.


  25. Mark

    We had problems with our connectivity to our cellular modems
    yesterday, June20. This happens occaisionally for short periods but
    yesterday it was for hours. We apologize, but these things happen.

    The best way to check you appointment was done correctly is
    to go to the home page and look up the schedule for the particular day
    you scheduled you pointing. There you can check the time and
    exact position. Clicking on the “map” link for your observation
    you can see if you wer in the proper place to see the light from solar beacon.

    Yesterday we were probably not pointing towards you.
    I recommend scheduling more pointings.

  26. was unable to see anything today, East Bay Kensington, 1:25 PM, there was some haze but I could not see anything. How do I confirm if my location was entered correctly ?

  27. Paul-
    The “quality factor” is an estimate of what fraction of the mirror’s area is reflecting
    the Sun to your location. It takes into account the angular projection of the tilted mirrors.
    So 100% means all the reflected light possible is heading your direction. This would be the case with the
    Sun directly behind you and the mirrors pointing straight at you. More likely, throughout the day
    the Sun is high in the sky and you are on the ground, so the mirror normal is tilted half way between
    the two directions, so the projected size of the mirror is less. Worst case is when the Sun is in the
    direction of the mirrors from your vantage point, and the mirror is pointed to a grazing incidence, edge on.
    In this case the quality factor is 0%. Since our eye’s response to light is logarithmic, 50% is still pretty bright,
    though anything less than 10% would be dissappointing. That is why we recommend mornings for East Bay
    and afternoons for the West side of the Bridge.

    The “f” and “b” correspond to the front and back sides of the Heliostat mirrors. We have 4 mirrors on
    each side, to increase our range of pointings, as the pan-tilt mount can’t swing 360 degs. The front mirrors are
    all co-aligned, but the back mirrors are purposely miss-aligned by about 0.5 degrees. This allows us to decrease the brightness
    by a factor of 4, which we do for the very closest pointings, < 2.5km. It also increases the beam size, increasing
    the area of the beam footprint so more people can see the light.

  28. The schedule has a column labelled ‘quality’ with a % value and the letter ‘f’ or ‘r’ appearing after the value. I looked for an explanation of this value, but couldn’t find one. Can you explain what the term quality refers to? BTW – I’ve made two appts. so far and really enjoyed it. I have a couple more scheduled. Thanks!

  29. Oh yeah, and I have seen the Golden Gate from the top of Mt Diablo. If you walk a hundred feet over the ridge west from the overlook parking lot you come out of some trees and see everything. It’s really spectacular. Now if I could have done that during the eclipse and Venus was in transit and somehow the solar beacon was blinking at me too I would have been REALLY impressed. Guess I’ll have to wait for that one.

  30. Henry the Dog and I thoroughly enjoyed our privately scheduled beacon show this morning from the side of Roundtop Mountain in Sibley Park in Oakland. We could see the distant south tower of the bridge just peeking over the hills to our west. Right on cue at 8:05 it started glinting the morning sun back at us. Cool. Then after a few minutes, it moved on to brighten someone else’s morning. Left and right brains were both most impressed. Thank you!

    I hope to check it out on a clear day from the top of Mount Diablo too.

  31. Thanks so much! It was an awesome birthday present for my daughter tonight (8PM) to see her giant birthday “candle” shining from the Golden Gate Bridge. She won’t forget her 29th birthday!

  32. Looked great in the Berkeley Hills at 2pm today! My dream is for you to be able to “blink” them at me rapidly enough for Morse code. I have a ham radio nerd who would pee his pants if I sent him a personal (1/2 degree) message from the top of the golden gate.

  33. Pleased to see this working so well. Congratulations! John, when do we see this here in London on Tower Bridge?

  34. FYI If your selected time is already taken and you use the back button on the browser, your map position is not retained.

  35. David,
    It not possible for the mirrors to point at the East Bay in the afternoon after about 3pm, and I’m working on a way to prevent users from entering points that the mirrors cannot point to to prevent an experience like yours. However, you not seeing the reflection is useful because now we really know it doesn’t work! (By the way, you won’t need any kind of magnifying device to see it.)

  36. Just had my scheduled viewing at 10:15 in the north Oakland hills. Very cool!

  37. The beacon was not visible from the Berkeley Marina Entrance (really Berkeley Pier entrance) location today (June 2) during the scheduled times beginning at 3:15 pm and 4:15 pm. I could see reflections from windows in SF and Marin with the naked eye, but nothing on the bridge towers with a high quality 10×25 monocular.

  38. Oh … the extra height of the Mount Diablo observation deck atop the summit building (37.881767° N 121.914243° W ) should nicely solve the problem of looking over the trees, particularly since at the right point on the deck (37.881767° N 121.914243° W ) the view to the Golden Gate lines up with the access road. Here’s a nice bird’s eye view showing the copper-topped summit building and its deck on the right. The line of sight from the north end of the observation deck to the Golden Gate bridge passes north (far side) of the radio tower, over the north access road to the parking lot.

  39. > trying out Solar Beacon to Mount Diablo and to Mount Hamilton (Copernicus Peak), and I don’t see why that wouldn’t work

    Trees are another possible problem when considering a viewing point.

    Zooming in on Mount Diablo at
    ( )
    the line to the Golden Gate from the parking lot on top looks to have an interference problem with the slightly higher hill on which the radio tower sits, and the neighboring trees. Google Maps Streetview reinforced that impression. I should think there’s some spot on the route up that has a tree-free clear view – this spot looks likely:

    [CA] Mount Diablo lower parking lot
    latitude 37.880004° N longitude 121.919419° W
    elevation 3700 ft above sea level (6 ft above ground)

    Hopefully the bridge is easy to spot with binoculars, but just in case, we usually note the magnetic bearing to the
    target ( the bridge is 248 deg magnetic from Mt Diablo), and bring a compass (even smartphones have compasses these days – not the best, but good enough to look in the right direction, if you make sure you stay clear of anything magnetic (e.g., don’t stand next to the car, chain link fence, etc.)).

    A great tool for looking in the right direction are the class of marine binoculars with a builtin compass that is superimposed below your view. Even low end ones, like my Fujinon-Mariner XL Series – Binoculars 7 x 50 WPC-XL, cost closer to $200 than to $100, though. But perhaps you have a nautical friend with a set who is willing to lend them out.

  40. Too freakin’ awesome. Tried out the scheduler, I realize it may not do anything at this point, but pls pls pls keep at it because it is too cool not to make it work. Will be passing the news.

  41. Richard,
    Thats very interesting, and I was not aware of that website before you told me about it. We were planning on trying out Solar Beacon to Mount Diablo and to Mount Hamilton (Copernicus Peak), and I don’t see why that wouldn’t work, unless there’s too much fog or smog, or because some atmospheric refraction effect

  42. > Webcams might be able to see the lights, but we have mostly been disappointed with inexpensive camera shots of Solar Beacon – they
    > just don’t seem to capture the brilliance of the light like your eyes do. We will check the LHS cam as it has an archive of the previous days shots.

    Inexpensive digital cameras just don’t have the dynamic range (at 8 bits/pixel/color intensity encoding) to capture the dynamic range of mirror flashes. At close range, lens flare will make the brightness apparent ( see the video below of flashes from a 3″x5″ mirror . at 0.7 mile range). I would think your mirrors would have a similar effect out to at least 2 mile range from the mirror.

    At longer ranges, using a “star filter” on the camera will help convey the brightness.

    Survival Signal Mirror Flashes at 0.7, 11.1, 43 mile range ” (YouTube)

  43. John,

    It was Tuesday, the 29th, of course…

    I emailed a picture I took with an iphone to your contact email (sb@…) Should have time and location info in EXIF data.
    Here is the some of the daqta
    Date taken : 2012:05:29 16:38:37
    Shutter speed [s] : 1/2045
    Aperture : F2.4
    Focal length (35mm) : 35
    Latitude Ref : North
    Latitude : 37° 47.52′ 0.00″
    Longitude Ref : West
    Longitude : 122° 29.03′ 0.00″
    Altitude Ref : Other
    Altitude : 0.0000

  44. Karl-
    We were not on the bridge on May 25th, but we were on Tuesday May 29th. There are times when the Sun angles are such that both mirrors cannot point to the same location, as we are at the limits of our Pan or Tilt axis range. Or something could have gone wrong. Can you
    tell us the exact time you saw the beam? This kind of feedback is very important, as we can’t be everywhere to check. We also occasionally loose cellular contact (just like phones!) so that also might explain. Thats why we need the time.

    Webcams might be able to see the lights, but we have mostly been disappointed with inexpensive camera shots of Solar Beacon – they
    just don’t seem to capture the brilliance of the light like your eyes do. We will check the LHS cam as it has an archive of the previous days shots.

  45. Is it possible to see it from the Lawrence Hall web cam? . When it’s clear the bridge towers are just visible, and I thought I could see the light on the north tower on May 30 (looked like about one yellow pixel), but haven’t been able to see it since.

    The confluence of science, technology and art is the kind of thing that makes San Francisco a wonderful place to live.

    Keep up the good work!

  46. I have seen the reflection on Baker Beach on Tuesday, May 25 around 16:38. Was a surprise.

    The light from the north tower was very bright, the other tower didn’t look as impressive. I biked around the parking lot to see if the light from the south tower would get brighter, but found only that the north tower light would get dimmer.

    Are both mirrors reflecting to the same spot or do they reflect parallel beams?

  47. I’m excited to see this project – long range signalling with reflected sunlight is my hobby, and there is an annual Scouting event where we signal from mountaintop to mountaintop with mirrors (typically 12″x12″ or 24″x24″) called “Operation On Target” (

    The rule of thumb for visibility with the naked eye in clear air is 10 miles per side width of the mirror in inches – a 12″x12″ mirror can be seen at 120 miles with the naked eye (I’ve personally witnessed one at 70 miles). It seems your collected mirror area is at least that much. From the tops of the Golden Gate Bridge towers, the farthest visible point on the ground is 73 miles (more on this below), so your mirror size should not be the limitation.

    In this video I put on YouTube, ( ) the flash from Keller peak (55 miles from the camera) is using a 9″x9″ mirror. Of course, some days haze/fog/smog means you can’t even see 10 miles, but as a rule of thumb, if the air is clear enough to see the peak, someone on the peak will see the mirror flash. Binoculars will help visibility, too.

    Regarding the locations with line of sight to your mirrors – there’s a nifty website called “” that shows what locations are visible from any point. I went ahead and entered your two mirror locations (746 ft above sea level, centered over the bridge piers) – you can see what the site says is visible from your locations at the two websites here:

    North MIrror Coverage Area:
    South Mirror Coverage Area:

    The locations marked with red triangles on the maps at those sites, you can “take to the bank” – they will be prominently visible.

    If your favorite location isn’t shown (all that is directly marked are selected prominent peaks), don’t give up – click on the “visibility cloak” button on the top right of the map. It will tint red any areas with line of sight to the mirror whose web page you are using.

    For a quick overview of the convex hull of the visible area, click on the link “view in Google Earth by day”, to get a file you
    can open in Google Earth, which will show this for you in Google Earth. In similar fashion to the web site, there will
    be a lower level checkbox (off by default) you can find if you expand the object in “places” list in Google Earth that
    will tint visible areas red.

    If you want to screen out unsuitable regions (no field of view) you could make a mask from the output of that program.

    It could also be useful to make up a list of suggested locations.

    I’m not familiar with your area, but the peaks on that list at that website would be good choices for people wanting to see it from afar –
    such as Cobb Mountain (69 miles North) and Copernicus Peak (57 miles south).

    The real imponderable is when there will be sun on the mirror vs. clouds overhead.
    Here’s a “clear sky” forecaster for the area, but my experience with this site is that it is, at best,
    good at predicting the high clouds visible to the GOES satellite – local fog, marine layer, smog, etc. – not so good.

    I’m looking forward to the scheduler – while I’m way out of range, I have a friend in Petaluma I hope to talk into trying it out!

  48. We are working toward interactivity as fast as we can. What we want is a reliable product that
    does not frustrate the user and that we are confident will work. If you make a special trip and the
    beam doesn’t show up, you might be a bit angry. Right now we are running some fixed schedules
    at fixed locations which are accessible from the home page.

    My guess is that it might be interactive by early next week, say June 3rd. This will allow us
    to test it over the weekend.

  49. When will the mirrors become interactive?

  50. You are correct, Anonymous and the text has been corrected. The sun is approximately 1/2 degree across and 0.5 deg at 2km is 17.45 meters. But the 4 mirrors on the Heliostat are not necessarily aligned that well, so there is a lot of play in these numbers. But 12 km was wrong.

  51. (e.g. 12m at 2 km)

    2 kilometers * (.5 degrees) = 17.4532925 meters


  52. My parents’ house is in El Cerrito with an excellent view of the GG bridge. It’s 12.5 miles as the crow flies or as the sun beams, I suppose. I put in a schedule for next Saturday when I’ll be there. hoping for a sunny day.

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  54. Chris, Mount Hamilton might work, but there’s a 100km limit at the moment for schedule locations. The scheduler does do some other checks, but it does not try to work out if you can see the bridge or not, figuring that you are in the best position to do that.

  55. Looks like fun! I will schedule a showing for Mt. Hamilton (57 miles) and maybe Loma Prieta, too (60 miles). I’ll try and pick a time when the sun angle is optimal.

    Another question: if I’m in SF in a location that only has line of sight to one of the towers because of a building in the way, will the scheduler be smart enough to figure out which mirror to aim my way? Or do they both get aimed at the same target?

  56. We have a button on the Scheduler that says “Try to set the marker to my location” which
    uses the location of the device you are using to access the internet. We do not
    know where the device is getting its information – GPS or cell towers or Internet delays.
    We like the map method as it re-enforces the brain to check the quality of the
    location. And you might want to schedule a performance at a different place than where
    your phone or computer is right now.

  57. We would like someone on Mt. Hamilton to try to see Solar Beacon. You
    can schedule a viewing with our scheduler by panning the map down to
    Mt Hamilton. Intensity drops as radius squared, so it won’t be as easy
    to see as from the East Bay, but maybe we should have a contest as to
    who can see Solar Beacon the furthest away!

  58. Consider expanding the available area to include South Bay peaks like Mt. Hamilton, Loma Prieta or Mt. Umunhum. I think these peaks all have line of sight to the GGB. It would be interesting to try at these extended distances.

  59. Great idea with solar beacon. Love this kind of interactive art. I was wondering (suggesting) you allowing GPS coordinates to be input in addition to cross-hairs on the map. I found an easy free application for my iphone called GPS Coordinates which gives me the coordinates of where I am (where my phone is) in that moment.

    Thanks….looking forward to trying this out.

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