November 17, 2021
Dear Mark,
Apologies for the delayed response. Unfortunately, due to pre-existing work commitments I simply did not have the time to fully consider the Zeiger report between receiving your request on Thursday night and the transmission of your rebuttal early on Friday afternoon.
I am afraid I cannot claim to have any great technical knowledge in as far as lighting engineering goes and I certainly have not had the chance to peruse the Zeiger report in depth. However, for what it's worth (and possibly for future reference) allow me to mention some of my broad brush impressions from scanning the Zeiger report:
+ I agree that the report may possibly be biased towards the billboard industry, since much of its inclusions and appendices appear to have been furnished by the industry/manufacturers and parroting the industry's message/agenda.
+ I'm not a lighting specialist, but the description of measuring in-the-field seems somewhat contrived, amateurish and unscientific.
+ I would strongly contest the Clear Channel slide entitled:
"LED: Contribute less to Sky Glow and Light Trespass"
As the very least, this statement is glib. At worst, it is misleading. It is most certainly factually incorrect:
Particularly in Santa Clara County, the introduction of LEDs *worsen* sky-glow:
a) due to the cross-spectrum nature of LEDs (as opposed to discharge lamps).
b) due to the "rebound effect" resulting proliferation of economic LED installations.
The directionality of the signs matters: From the perspective of Lick Observatory, aiming electronic billboards to face the road contributes *more* to light trespass, not less.
The contribution of horizontal louvres to suppression of sky glow is minimal and is more-than-outweighed by the surface area of the proposed billboards, their height and resulting beam path to the nearest surfaces:
Ever-present aerosols (e.g. water vapor, particulates, etc.) preferentially scatter and redirect light. Blue wavelengths scatter more than red wavelengths.
The greater the path length from the point of emission to any opaque absorbent surface results in *adding* to the intensity of vexatious sky glow.
+ In describing the light produced by the billboards, several references are presented in comparison to "ambient" lighting. In my view, this completely misses the point:
Anthropogenic Light At Night (ALAN) produces negative consequences on flora, fauna, and human well-being. 99% of people in the US no longer experience a truly dark night. 37% of the people in the US do not use their natural night vision. Tragically, 80% of children born in the western world today will never know a night dark enough that they can see the Milky Way. Residents of the conurbations in the Santa Clara valley are no exception.
As more light fixtures are added to the ever-expanding conurbations, so the background/ambient scattered light increases. Certainly, the issue has worsened over time. In early October 2021, during the UN-sponsored international conference "Dark & Quiet Skies II" an acceleration in ALAN of between 49% and 270% was reported over the past 25 years. In specific areas (e.g. rapidly developing conurbations in the industrialized world) this figure could be as high as 400%.
Thus, any thresholding, comparative to ambient, only promises to exacerbate the fundamental problem of ever-increasing ALAN, albeit at some "pseudo-measured" rate: it becomes a "race to be the brightest".
With appreciation for your efforts to combat the proliferation of ALAN.
Sincerely,
Paul Lynam
Astronomer
UCO/Lick Observatory