Page 84 - Between light and shade

between light and shade, TRANSPARENCy and reflection

Industrial production of the incandescent
filament bulb, at the end of the 19th century,
followed by that of fluorescent tubes in around
1930, also revolutionised our lifestyle and
construction methods. The incandescent bulb 96,
with luminous efficacy of 10 to 20 Lm/W and a
standardised useful life of 1000 hours 97, provided
luminous flux of 740 Lm for 60 W and a color
rendering index (CRI) of close to 100%, as well
as a colour temperature of between 2400 and
2700°K. It became the universal lighting source.
Fluorescent tubes are even more powerful,
with luminous efficacy of 80 to 100 Lm/W (for
example, luminous flux of 3000 Lm for 36 W), a
usable life that can reach up to 12000 hours and a
colour temperature of between 2700 and 6500°K,
as required. These performances are achieved at
the expense of a standard color rendering index
(CRI) of just 80%, which, for a long time, restric-
ted their use in industrial buildings or offices.

However, there are tubes with a color rende-
ring index (CRI) approaching 95%, (but with
a loss of luminous efficacy of 5 to 10%). Their
quality of light, although a little “colder” (4500°K
instead of 2700°K), is as good as that of the incan-

96 It is virtually no longer manufactured, as its sale was perma-
nently prohibited within the European Union on 31st Decem-
ber 2012.
97 This planned obsolescence by the Phoebus cartel from 1924

onwards, represents a technical compromise between luminous
flux, luminous efficacy, color rendering and usable life.

84