Technical information

4
6
8
.1
Ni
g
h
t v
i
s
i
o
n
The luminous
f
lux
,
measured in lumens
,
is the irradi
-
ated output o
f
a li
g
ht source evaluated by the eye. It
is de
f
ined by multiplyin
g
the physical radiation output
with the e
y
e sensitivit
y
curve V
(
λ
)
.
S
tandard luminous
f
lux measurements onl
y
consider the reaction o
f
the
eye at hi
g
h illuminance levels
(
photopic vision
)
as is
typical
f
or dayli
g
ht and indoor illumination. Luminous
f
lux measurements measure photopic li
g
ht as per
-
ceived by the central re
g
ion o
f
the eye
.
W
hen the illumination level is ver
y
low,
f
or example at
n
igh
t
b
y star
ligh
t, t
h
e v
i
s
i
on con
di
t
i
ons are sa
id
to
b
e
scotopic. The reaction o
f
the eye chan
g
es under these
circumstances. The e
y
e sensitivit
y
curve
f
or low illumi
-
nation levels
(
less than 0.1 cd
/
m²
)
is the V'
(
λ
)
curve, as
shown in the
f
i
g
ure 43
.
S
ensitivity for red and yellow li
g
ht decreases, while
there is better perception o
f
blue li
g
ht. When luminous
f
lux is measured under
p
hoto
p
ic conditions, this does
not correspond to what the eye perceives at low li
g
ht
levels. The reaction o
f
the eye does not chan
g
e sud
-
denly
f
rom hi
g
h to low illumination levels. The chan
g
e
i
s
g
ra
d
ua
l
w
h
en t
h
e
ill
um
i
nat
i
on
l
eve
l
d
ecreases to
tw
ili
g
h
t an
d
typ
i
ca
l
street
li
g
h
t
i
ng con
di
t
i
ons.
Thi
s
i
s
ca
ll
e
d
mesop
i
c v
i
s
i
on w
hi
c
h
li
es
b
etween p
h
otop
i
c an
d
scotop
i
c v
i
s
i
on
.
T
he chan
g
e in eye sensitivity comes
f
rom the presence
of two types of light receivers on the retina: rods and
cones. The rods are res
p
onsible
f
or vision under low
illuminance and are located in the peripheral
f
ield o
f
v
i
s
i
on.
Th
e ro
d
s are sens
i
t
i
ve to scotop
i
c
ligh
t w
hil
e
t
h
e cones react to p
h
otop
i
c
ligh
t.
Wh
en t
h
e
ill
um
i
nat
i
on
level decreases
,
the rods are there
f
ore more active
,
w
hil
e t
h
e cones
b
ecome
i
nact
i
ve.
T
he e
ff
ective
,
seen “lumen” will di
ff
er
f
rom the mea
-
sured
p
hoto
p
ic luminous
f
lux. When the illumination
level
f
alls, the e
ff
ective “luminous
f
lux”, e.
g
. o
f
yellow
hi
g
h
-pressure so
di
um
l
amps,
d
ecreases w
hil
e t
h
e
e
ff
ective “luminous
f
lux” o
f
white li
g
ht with a hi
g
her
share of
g
reen
/
blue li
g
ht increases
.
Fi
g
ure 47 shows the radiation output of a H
C
I
®
-T
C
70 W
/
NDL and a NAV
®
-T 400 W
S
u
p
er 4Y, normalized
in the interests o
f
comparabilit
y
to a luminous
f
lux o
f
1000
l
m.
Th
e
di
a
g
ram s
h
ows t
h
e re
l
at
i
ve
di
str
ib
ut
i
on
o
f
the radiation in the spectrum
.
Weighting factor for eye sensitivity curve
Fig
. 47:
Phy
s
i
ca
l
ra
di
at
i
on output
i
n
W
per 1000
l
m an
d
per 5 nm
I
n
Fig
. 48, t
h
e p
h
ys
i
ca
l
ra
di
at
i
on output
h
as
b
een mu
l-
tiplied b
y
the V
(
λ
)
curve to ascertain the luminous flux
per 5 nm in each case. Inte
g
ration o
f
the values
f
or all
w
ave
l
en
g
t
h
s
b
etween 380 nm an
d
780 nm resu
l
ts
i
n
the specified 1000 lm for both li
g
ht sources
.
The
NAV
®
l
amp ra
di
ates more
ligh
t
i
n t
h
e ran
g
e aroun
d
580 nm, which is near the maximum of the V
(
λ
)
curve.
This contributes to a hi
g
h luminous efficacy.
O
n the
ot
h
er
h
an
d
, t
h
ere are some
g
aps
i
n t
h
e spectrum,
particularl
y
in the blue part of the spectrum, which is
responsible
f
or the poorer colour renderin
g
compared
to t
h
e meta
l
h
a
lid
e
l
amp
.