Page 81 - Between light and shade

Light, transparency and reflection

but, to the best of my knowledge, never again
since then.

While a polyester-PVC or fibreglass-ETFE
membrane (with light transmission of just 10%)
cannot reasonably cover a span of more than
20m, a 1mm-thick, 60%-perforated steel sheet
membrane coated with a transparent ETFE film
(therefore with light transmission (LT) ≥ 55%)
could easily cover a span of more than 50m using
an S690 steel and up to 70m using an S2000 steel!
from candles to Leds
At the end of the day, when night falls, artificial
light sources enable man’s activities to continue.
In effect, it is not possible to rely on a full moon,
whose luminous flux is just 0.25 Lm, only provi-
ding illuminance of 0.25 Lx on the ground.

Outside, the large wood fires, around which
people settled, took over with their magical
interplay of light and shadow but, inside, our
ancestors had to be content with light from the
hearth and candles, whose luminous flux reaches
approximately 10 Lm (illuminance of the order
of around ten Lx for a candle placed on a table):
the empire of the shadow.

Fortunately, the illuminance needed for
a comfortable illuminated atmosphere also

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