Here - PMOD/WRC

New photometric standards development at NIM-Romania
M. Simionescu, A. Seucan
NIM-Romania
J. Bastie, A. Stepnik
LNE-INM, France
Abstract. Traditionally the National Institute of
Metrology of Romania (NIM-Ro) used to maintain
the luminous intensity and the luminous flux units on
groups of specially designed lamps periodically
calibrated by the Photometry Laboratory of the
BIPM. Following the closure of the calibration
service of this laboratory, it was decided to proceed to
independent realization of the candela and subsequent
goniophotometric derivation of the lumen.
Accordingly, during 2002-2003, the candela was
realized on the basis of a trap radiometer traceable to
the LNE-INM (France) primary reference. To validate
the new realization several internal and bilateral
comparisons were organized, with good results.
Following, a group of three similar absolute
photometers were developed at NIM-Ro in order to
be used as the new national (group) reference. To
validate both the new standards and the
corresponding transfer capabilities, bilateral
comparisons were organized with LNE-INM, within
the EUROMET 823 project. Theoretical basis,
design solutions and so far obtained results are
reported. Key words: luminous intensity, luminous
sensitivity.
1 Theory
The luminous intensity (I v ) of a point source, placed
at a distance d from a photometer, is [1, 2]:
2
d F
I
v
= K
m
⋅ ⋅ ⋅Yph
(1)
A sm
where:
Y ph = the photocurrent generated by the photometer;
K m = the maximum luminous efficacy of the CIE
standard observer (683 lm / W);
d = the lamp-photometer distance (m);
s m = the peak absolute, spectral responsivity of the
photometer (A/W);
A = the effective area of the photometer aperture
(m 2 );
The spectral matching factor F employed in (1) is :
F =
∫
∫
S
S
() λ ⋅V()
λ ⋅
() λ ⋅ s () λ
r
dλ
dλ
(2)
where S(λ) is the relative spectral power density of
emitted flux and V(λ) is the relative luminous
efficacy function of the CIE standard observer [3]
and s r (λ) is the relative spectral responsivity of the
photometer defined with:
s r (λ) = s(λ) / s m (3)
Such a photometer is intrinsically characterized by
it`s luminous sensitivity:
A⋅
sm
sv
= (4)
K ⋅ F
Using such an absolute photometer the luminous flux
unit may be derived and transferred to secondary
standard lamps using the NIM designed
goniophotometer. Basically, the total flux is given by
:
Φ
v
=
π / 2 2π
∫ ∫
v
−π
/ 2 0
m
I ( α,
θ ) ⋅ sinθ
⋅ dθ
⋅ dα
= K
m
2
d ⋅ F
A ⋅ s
π / 2 2π
∫ ∫
Y
ph
m −π
/ 2 0
⋅ sinθ
⋅ dθ
⋅ dα
where α and θ are, respectively, the azimuth and the
polar, angles.
2 Practical realization of the candela
A filtered trap detector using three Hamamatsu S
1337 1010 BQ windowless photodiodes was used.
The basic design of the photometer’s transducer and
general set up are shown in Fig. 1.
Figure 1. Candela realization at NIM; Experimental set up
3 Characterization and first comparison
Work was conducted within a bilateral cooperation
project [4]. The absolute and relative spectral
responsivity of the new photometer was measured
against the NIM-Ro reference radiometer, traceable
to the LNE-INM primary standard.
Detailed characterization of the photometer led to the
following values: s v,NIM-Ro = 9,5678 nA/lx; u c =
0,45%.
To check these figures, a bilateral comparison was
organised with LNE-INM [5].
The results are synthesized in Tab. 1.
s vFA02
NIM-Ro
s vFA02
LNE-INM
∆s vFA02
Comp.
combined u c
Proceedings NEWRAD, 17-19 October 2005, Davos, Switzerland 317