On Thu, 11 Oct 2012 09:47:40 -0700, Jeff Liebermann
wrote:

On Thu, 11 Oct 2012 03:13:01 -0400, "Michael A. Terrell"
wrote:

Jeff Liebermann wrote:

On Mon, 8 Oct 2012 06:27:05 -0700 (PDT), George Herold
wrote:

Hi SEB. Well I sent an email to Don klipstein on this topic. And
have permission to copy his reply.
from Don K. below

2: In incandescent traffic signals, the bulbs for yellow last
longer than for red and green. So even after being switched on
and off about a million times, on-time is still a significant
factor in life expectancy.

That means for my proposed test comparing a 50% duty cycle flashing
light bulb, with one that is on continuously, the continuous light
bulb will burn out first. That's the opposite of what I saw with the
theater marquee bulbs. Now, I'm really tempted to run the experiment.

Was there any vibration in that theater marquee?

Nope unless you count the movie audio pumped in from the theater
section as vibration.

The lobby and foyer lights were probably on a different circuit from
the marquee lights, which may have had different voltages, glitches,
surges, etc. I suspect that there were also some switching
transcients on the marquee side. That was 45 years ago, and I didn't
think to measure any of that. I just kept replacing light bulbs.

I have a yet another guess(tm). I think the failures may have been
due to heating.

The lobby and foyer lights were mounted on the ceiling, pointing down.
One would think that there would be plenty of hot air accumulating
near the ceiling, but that wasn't the case. That's where the fan
ducts were located which helped to cool the lights. Few of those
lights ever burned out.

The marquee lamps were mounted on a vertical structure, with the lamps
pointed horizontally. I recall about 15-20 rows of lights. The
backing was some type of sheet metal and plywood sandwich possibly to
prevent the heat from the lights from setting fire to the building.
Near the top was about a 2ft overhang, which was mostly decorative,
but was also was used to hang flags and announcements. The rising hot
air from the lower lamps would accumulate under the overhand and
thoroughly heat the top rows of lights. Unfortunately, I didn't
notice which rows required the most lamp replacements.

One evening, I was volunteered to replace two lamps that had burned
out when the marquee was run for some occasion. I recall that the
sheet metal or plywood backing was warm near the bottom, but rather
hot near the top. This was about 10 minutes after the marquee was
turned off so that I could replace the bulbs. (That was also with a
line of people standing under the ladder, which was not very safe).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558