monument lighting

[Jan Hollan <jhollan@amper....muni.cz>]

Thanks Ian,

Lucy Ash wrote me this noon where she should send the CD... its arriving
already.

In fact, there is a way to have a non-offending architectural lighting
compatible with the historic buildings and the sky above (apart from a
need to keep its geometry strictly confined to the building itself): as in
the two laws in Italy already, in Lazio (including Roma) and Marche (on
the east coast, with Ancona). They have an upper limit of average
luminance of the lit surface, 1 cd/m2, if no safety rules demand more.
Just in case of roads, there are such rules, asking sometimes up to
2 cd/m2 (it is doubtful, if the value is a true safety demand, as it
went steadily up the last century, being rather a technically
easily achievable value).

1 cd/m2 can be achieved with some 6 lux having a mat face absorbing just
half of the light. But that much is mostly not needed. 

In case of facades, another reasonable demand is they should not be
brighter than the surroundings. No need for them to be twice brighter than
the road, even half the luminance of the road would make them visible very
well. And not spoiling the adaptation of the eye, if the safety is a goal
-- the eyes should be perfectly adapted just to the vital scenery, to the
path.

Both demands are included in the detailed Italian text on the outdoor
lighting -- a sort of an English version is available as a pdf on my
messy pages (7 MB)
  http://amper.ped.muni.cz/light/VISUALreg17eng.pdf
 or as a (at my computers not well functioning) M$word file on the Italian
ones,
  http://www.vialattea.net/cielobuio/supporto/visualreg17eng.zip

Extremely high luminances of the lit monuments, as recommended by CIE, are
surely a consequence of the silent assumption that many glaring luminaires
are in the same direction and the lit surface has to be conspicuous even
with a lot of interference. All directions, from which the monument should
be adequately (decently) visible at night, should be adapted so that no
lamps are visible there. Then the monument may be most appealing in a
negative contrast, as dark against the sky. If a positive contrast is
really needed, very low amount of light may do.

Jenik

PS. 
 your wonderful letter on historic monuments is online, 
  http://amper.ped.muni.cz/jenik/letters/public/msg00076.html