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Detailed Comparison of Illuminance Scale Realizations of KRISS and TKK
Seung-Nam Park, Dong-Hoon Lee, Yong-Wan Kim, In-Won Lee,
* Erkki Ikonen, * Mart Noorma and * Farshid Manoocheri
Division of Optical Metrology, Korea Research Institute of Standards and Science (KRISS) PO Box 102, Yuseong,
Daejeon 305-600, Korea
*Metrology Research Institute, Helsinki University of Technology (TKK) and Centre for Metrology and
Accreditation (MIKES) P.O. Box 3000, FI-02015 TKK, Finland
Abstract. A detailed comparison of the illuminance
realizations of KRISS and TKK is performed. The relative
difference of spectral responsivity at 555 nm is
(-0.3±0.8) %, while the difference of the color correction
factor for the illuminant A is (0.28±0.38) %, and the
expanded uncertainties are given for coverage factor k=2.
The area measurement for the radiometric aperture agrees
within (-0.04±0.06) %. Accordingly the difference of the
illuminance responsivity is (-0.6±0.8) %. A direct
comparison of the illuminance responsivity scales which
are realized and maintained by the procedure of each
institute shows an agreement of (-0.1±0.9) %.
I. Introduction
Since the candela as well as the related quantities are
generally derived from illuminance, accurate realization of
the illuminance is critical in photometry and radiometry.
However, as realizing the illuminance scale requires a
series of measurements, such as responsivity, spectral
characteristics and aperture area of a photometer, a set of
comparisons for only illuminance responsivity between
NMIs as in the case of the CCPR-K3.b [1] may be
insufficient for an appropriate guide to improve the
uncertainty.
In this paper, the measurement processes for the
illuminance realization, such as the spectral responsivity at
555 nm, color correction factor for the illuminant A and
the aperture area of the artifact photometer are in parallel
compared between KRISS and TKK. Finally, the
illuminance scales realized and maintained by both
institutes are also compared to give material for a
discussion on the comparison of the measurement
processes.
II. Detailed Comparison of Illuminance Scale
Realizations
The illuminance responsivity of a photometer is
obtained by the equation
A⋅
S555
Rvi
= (1),
683 lm/W ⋅ f () e
where A is the aperture area, S 555 the absolute spectral
responsivity at 555 nm, and f(e) the color correction factor
(ccf). The ccf is defined as
∫ e( λ) V ( λ)
dλ
λ
f () e ≡
(2),
e λ s λ dλ
∫
λ
( ) ( )
where e(λ) is relative spectral power distribution of the
source and s(λ) the normalized spectral responsivity of the
photometer.
The artifact photometer for the comparison consists of
a temperature-stabilized photometer head supplied by
LMT and an external aperture of 7 mm diameter. The
edges of the aperture were trimmed by a diamond-turning
machine. The artifact was transferred to TKK after
measurement at KRISS and then returned to KRISS for the
drift check.
At KRISS, the illuminance scale is realized by
calibrating spectral responsivity of the photometers using a
spectral responsivity comparator traceable to the absolute
cryogenic radiometer. Relative spectral responsivity is
measured against the single element silicon reference
detector, while the absolute responsivity at 555 nm is
compared to the silicon trap detector. The aperture area of
the photometer is measured by two independent methods,
Gaussian beam superposition (GBS)[2] and optical edge
detection (OED). The OED method can be easily
implemented by inserting a microscope and focusing the
beam on the aperture plane in the GBS.
Relative Spectral Responsivity
1
0.1
0.01
0.001
0.0001
0.00001
KRISS
TKK
0.000001
300 500 700 900
Wavelength /nm
Figure 1. Relative spectral responsivity comparison of the
artifact photometer.
As far as the spectral characteristics measurement of
the photometer for the illuminance realization is concerned,
TKK has the procedure different from KRISS.[3].
However, TKK measured the spectral characteristics of the
artifact by comparison to the spectral responsivity
reference. For the comparison, TKK used the spectral
responsivity facility [4] and the reference trap detector
which is traceable to the cryogenic radiometer.
Figure 1 shows a comparison of the relative spectral
responsivity. The spectral bandwidths of the measurements
at TKK and KRISS are 1 nm and 4 nm, respectively. Even
Proceedings NEWRAD, 17-19 October 2005, Davos, Switzerland 325