Optics: measuring and testing – Plural test
Reexamination Certificate
2000-02-09
2003-03-18
Evans, F. L. (Department: 2877)
Optics: measuring and testing
Plural test
C356S319000, C250S461100
Reexamination Certificate
active
06535278
ABSTRACT:
This application is based on patent application Hei.11-31815 filed in Japan, the content of which are hereby incorporated by references.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus and a method for measuring a spectral property of a fluorescent sample including a fluorescent material.
2. Description of the Related Art
Generally, a visual property of a fluorescent sample including a fluorescent material is shown by a total spectral radiant factor. The total spectral radiant factor is a ratio by each wavelength of an emitted light from a sample which is illuminated under a predetermined condition against an emitted light from a perfect reflection diffuser illuminated under the same condition. The total spectral radiant factor Bt(&lgr;) is shown by the following equation (1).
Bt
(&lgr;)=
Br
(&lgr;)+
Bf
(&lgr;) (1)
Hereupon, Br(&lgr;) is a reflecting spectral radiant factor owing to a reflected light component from the fluorescent sample and Bf(&lgr;) is a fluorescent spectral radiant factor owing to a fluorescent light component from the fluorescent sample.
A fluorescent sample having a spectral excitation effect F(&mgr;, &lgr;) is generally excited by a light having a wavelength &mgr; in ultraviolet (hereinafter abbreviated as UV) region included in the illumination. Thus, the fluorescent spectral radiant factor Bf(&lgr;) is shown by the following equation (2).
Bf
(&lgr;)=∫
UV
I
(&mgr;)·
F
(&mgr;,&lgr;)
d&mgr;/L
(&lgr;) (2)
Hereupon, I(&lgr;) is a spectral intensity distribution of an illumination light and L(&lgr;) is a spectral intensity distribution of a standardized illumination light. As can be shown by the above-mentioned equation, the fluorescent spectral radiant factor Bf(&lgr;) depends on the spectral intensity distribution of the illumination light.
When a standard non-fluorescent white sample, in which a reflection spectral radiant factor Br
w
(&lgr;) thereof is known, is measured by a calorimeter, spectral intensities of the emitted light from the standard sample and the reference light are respectively designated by S
w
(&lgr;) and R
w
(&lgr;). When a fluorescent sample is measured by the calorimeter, spectral intensities of the emitted light from the fluorescent sample and the reference light are respectively designated by S(&lgr;) and R(&lgr;). The total spectral radiant factor Bt(&lgr;) of the fluorescent sample is shown by the following equation (3).
Bt
(&lgr;)=
Br
w
(&lgr;)·{(
S
(&lgr;)/
R
(&lgr;)}/{
S
w
(&lgr;)/
R
w
(&lgr;)} (3)
As mentioned above, the total spectral radiant factor of the fluorescent sample depends on the spectral intensity of the illumination light, so that it is necessary to coincide the spectral intensity distribution of the illumination light with the spectral intensity distribution of an assumed illumination light used for the measurement.
As an illumination light, a standard D
65
illuminant (day light) and a standard A illuminant (incandescent lamp) are well known. Furthermore, D
50
, D
55
and D
75
illuminants (day light) and F
1
, F
3
and F
11
illuminants (fluorescent lamp) are known. Spectral intensity distribution of these illuminants are defined by CIE (Commission Internationale de I'Eclairage).
In the estimation of the fluorescent sample, it is preferable to use the standard D
65
illuminant as an illumination light. It, however, is difficult to obtain an artificial illuminant similar to the standard D
65
illuminant. Thus, a relative UV intensity of an illuminant, which is a ratio of the intensity of the illuminant in the UV region against that of the visible region, is calibrated by Gaetner-Griesser method (See “Assessment of Whiteness and Tint of Fluorescent Substrates with Good Instrument Correlation” Rolf Griesser, “The Calibration of Instruments for the Measurement of Paper Whiteness” Anthony Bristow/COLOR Research and Application Vol.19 No.6 December 1994).
Details of the calibration of the relative UV intensity of the illuminant is described with reference to FIG.
9
. As can be seen from
FIG. 9
, a fluorescent sample
1
is disposed at a sample aperture
21
for sample of an integration sphere
2
. A lamp
101
such as a xenon lamp having a sufficient UV intensity is driven by an emitting circuit
104
. A light flux
102
emitted from the lamp
101
enters into the integration sphere
2
through a light source aperture
23
. A UV cutoff filter
103
is provided in a manner to cut the light flux
102
partially. A component of UV is removed from the light flux
102
passing through the UV cutoff filter
103
. Thus, the relative UV intensity of an illumination light can be calibrated by adjusting the position (insertion ratio) of the UV cutoff filter
103
.
The light flux
102
in the integration sphere
2
is diffusely reflected by an inner surface of the integration sphere
2
, and diffusely illuminates the fluorescent sample
1
. A radiant light
11
radiated from the fluorescent sample
1
passes through an observation aperture
24
and enters into a first spectroscope
105
used for measuring a spectral intensity distribution S(&lgr;) of the fluorescent sample
1
. A reference light
62
having substantially the same spectral intensity distribution of the illumination light enters into an optical fiber
61
by which the reference light
62
is guided to a second spectroscope
106
. Thus, the spectral intensity distribution R(&lgr;) of the reference light
62
is measured by the second spectroscope
106
.
For calibrating the relative UV intensity, a non-fluorescent white standard sample
12
, in which the reflection spectral radiant factor Br
w
(&lgr;) thereof is known, is disposed at the sample aperture
21
. A spectral intensity distribution S
w
(&lgr;) of a radiant light from the fluorescent white standard sample
12
and a spectral intensity distribution R
w
(&lgr;) of the reference light are measured. Subsequently, a standard fluorescent sample
13
, in which one of perceived color value such as a CIE whiteness thereof is known, is disposed at the sample aperture
21
. A spectral intensity distribution S(&lgr;) of a radiant light from the standard fluorescent sample
13
and a spectral intensity distribution R(&lgr;) of the reference light are measured. After that, a total spectral radiant factor Bt(&lgr;) of the standard fluorescent sample
13
is calculated by the above-mentioned equation (3). When the value of the CIE whiteness obtained by using the total spectral radiant factor Bt(&lgr;) of the standard fluorescent sample
13
is not coincide with the known value of the CIE whiteness of the standard fluorescent sample
13
, the position of the UV cutoff filter
103
is adjusted until the calculated a value of the CIE whiteness of the standard fluorescent sample
13
coincides with the known value. In this case, the above-mentioned equation (2) is modified to the following equation (4). Hereupon, the symbol “p” designates an attenuation factor in the UV region.
Bf
(&lgr;)=∫
UV
p·I
(&mgr;)·
E
(&mgr;,&lgr;)
d&mgr;/L
(&lgr;) (4)
As mentioned above, the Gaetner-Griesser method needs to move the UV cutoff filter
103
, so that the configuration of the apparatus is mechanically complex. Furthermore, it is necessary to repeat the movement of the UV cutoff filter
103
and the measurement of the samples
12
and
13
for calibrating the relative UV intensity, so that time will be wasted for the calibration.
For solving the disadvantage of the Gaetner-Griesser method, an apparatus shown in
FIG. 10
is proposed (See U.S. Pat. No. 5,636,015). As can be seen from
FIG. 10
, a first illumination unit
111
and a second illumination unit
121
are provided. A first light flux
113
including a UV component is emitted from a lamp
112
of the first illumination unit
111
and enters into the integration sphere
2
through a first illuminant aperture
22
. A light flux including a UV component is emitted from a lamp
122
of the first illumination unit
121
and a U
Evans F. L.
McDermott & Will & Emery
Minolta Co. , Ltd.
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