Frequently Asked Questions


How do you make the light at the top of the Tower so bright?

The light is reflected Sunlight and as bright as the Sun, though much smaller in size.  We use a Heliostat to keep the Sun’s reflected beam pointed where we want.

What is a Heliostat?

A Heliostat (Helios=Sun, stat=stationary) is a device that keeps a reflection of the Sun’s light pointed to a fixed position, even as the Sun moves across the sky (due to the Earth’s rotation). We use a computer controlled Pan-Tilt mount to keep the mirrors at the correct angle, knowing the Sun’s position.

Is it Solar powered?

Yes, the bright light is all from the Sun.  We use a few watts of AC power from the Tower to run the mounts, saving us the need to use photovoltaic arrays and (non-green) batteries.

How do you know the Sun’s position?

The sun’s position on the sky was worked out by astronomers centuries ago. Knowing the time of day and the location of the Heliostats, we use algorithms and formula to calculate what angles to project the solar beam to the observer’s location.

Can everyone see the light that I see?

No, only those in the expanding beam which is a half degree across.  A half degree corresponds to 8.5 meters at 1km, 170m at 2km. etc.  However, the beam can be pointed anywhere in the Bay Area that can also see the top of the Berkeley Campanile on its Western or Southern sides. You can schedule a pointing of the beam to a fixed location at a set time by going to the Scheduler page on the website

Is it safe to look at?

Yes.  Since the mirrors are on the top of the Tower, they appear small to all observers and therefore only reflect a very small fraction of the Sun’s surface.  You might not notice it, but you see Solar reflections all the time, from automobile mirrors, surface of the bay, pieces of metal, or large picture windows.  Solar Beacon was designed to be eye safe  by factors of 10 to 100, even for continuous viewing.

 Can it hurt Pilots or passengers in planes?

No.  Not only will they normally be farther away from the mirror than ground observers, they will fly through the beam at a very high speeds, so if they happen to be looking at the Tower, and the beam happens to be pointing up in the sky, passengers and pilots would only see a glint of light (if they fly through the beam).  Remember, Pilots are not currently harmed by the Sun, and if they look at the Sun, they quickly look away. Reflections of the Sun from oceans and lake surfaces are much more intense, as they are larger.

Can it hurt birds?

No.  Birds are not bothered by the Sun, so they shouldn’t be bothered by Solar Beacon. The same argument for Pilots can be applied towards birds: because they are flying fast, they will only see a glint of light as they fly through the beam, similar to what they see often in the urban environment such as  side view mirrors on trucks and cars and reflections from the ocean and the lakes.

How did you get that up the top of the Campanile?

We took the heliostats and their mounts up the Campanile elevator to where the bells are located, which is open to the public. We then went through the special (locked) door and took them up the narrow spiral staircase to the balcony level, which is off limits to the general public. It was installed there under supervision of the University representatives who inspected all of our designs and equipment before and after installation to make sure we did not permanently impact the historically significant tower.

 Posted by at 8:33 PM