NATIONAL BUREAU OF STANDARDS

NBS PROJECT

0201-20-0203 January 28, 195^

SPEC'TRAL TRANSMITTANCE

OP1 A

BLUE GLASS PHOTOMETRIC FILTER

REPORT ***' ly

NBS REPORT

3078

by

Photometry and Colorimetry Section

Optics and Metrology Division

to

Dr* Y » Nakaji. Associate Director

Electrotechnical Laboratory

Tokyo, Japan

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

The publication, rep Approved for public release by the

unless permission is Director of the National Institute of

25 ,d.c, Suchpem standards and Technology (NIST)

cany prepared if th on October 9, 2015

n part, Is prohibited

ndards, Washington

iort has been speclfiaort for Its own use,

SPECTRAL TRANSMITTANCE

OF A

BLUE GLASS PHOTOMETRIC FILTER

by

Photometry and Colorimetry Section

Optics and Metrology Division

ABSTRACT

The spectral transmittance of the

filter was measured over the wavelength range from bOO to 750 millimicrons. The values are given in

Table 1. 'The luminous transmittance

for 23o5°K derived from these values

is 0.5bb, compared with a value of

G.5V3 obtained by direct measurement

with the physical photometer.

1. INTRODUCTION

These measurements were undertaken in accordance

with a request initiated by Dr. Nakaji in discussions

with Mr. Barbrow at the Paris meeting of the Advisory

Committee on Photometry of the International Committee

on Weights and Measures in 1952. Correspondence relating

to this was received from Dr. Nakaji under dates of

March 2 and April 25, 1953 to Mr. Barbrow, with a second

letter dated April 25 from Dr. Nakaji to Dr. Gibson.

Mr. Barbrow 1 s reply to Dr. Nakaji was made under date of

March 11, 1953. The glass was received from the Japanese

Embassy in Washington in May, 1953.

In accordance with a letter from Dr. Nakaji to Mr.

Barbrow dated November 2b, 1953 > Mr. I. Honjoh visited

the National Bureau of Standards on January 5> 195*+ and

conferred with Messrs. Barbrow and Gibson. The blue

glass was returned to Mr. Honjoh at that time, together

with a table of the spectral transmittance values as

reported herein.

- 2 -

2 . MATER IAL

The glass measured is of the type designated as

cobalt blue. It is similar to the glasses measured by

the Bureau during 1928-32 in cooperation with the

national laboratories of Britain, France, and Germany

(Glasses Bl-28, R2-28, 13-28, R4--28, Annexe No. 4-0,

page 307, Proces-Verbaux des Seances* volume 16,

Annexes du Comite Consultatjf d 'Electr icite e t de

Photometrie, 1933), which served to extend tht, unit

of luminous intensity from the freezing point of platinum to higher color temperatures.

The present glass is approximately 2 inches square

and 1.4-9 tun thick and bears the designation "DSII" on

a small triangle of paper glued to the glass. The

glass is slightly non-uniform in thickness.

3 . S PEC TRO PHO TOME TR IC MEASUREMENTS

Measurements were made on three of the NBS spectrophotometers: (1) General Electric recording spectrophotometer with slit widths approximating 4- m/x of spectrum,

(2) General Electric recording spectrophotometer with

slit widths approximating 10 m/x of spectrum, and (3)

Beckman quartz (DU) spectrophotometer with slit widths of

1 to 2 m/x of spectrum. In all cases the temperature

of the glass was kept close to 25°C.

4-. SPECTRAL TRANSMITTANCE

Examination of the data from the three instruments

indicated that there were sLight errors at certain wavelengths in the values obtained with the General Electric

spectrophotometer having the wide (10 m/x) slits. It was

accordingly decided to take the averages of values

obtained with the other two instruments (General Electric,

4- m/x slits, and Beckman, 1 to 2 m/x slits) for use in

this report. These values are given in Table 1 attached.

However, at any wavelength, the average of the data from

the three instruments does not differ from the respective

value given in Table 1 by more than 0.003; at most

wavelengths the difference is less than 0.001.

The values of Table 1 are uncertain in the third

decimal

.

5. LUMINOUS TRANSMITTANCE

The value of luminous transmittance for a source

at 2365°K ( Co = 14-380 micron degrees) derived from the

values of Table 1 by the usual summation procedure is

0.544.

Direct measurement of this quantity on the NBS

physical photometer gave a value of 0.543.

- 4 -

Table 1

Spectral Transmittance of Cobalt Blue Glass

Submitted b} Dr. Y. Nakaji, Associate Director

Elec trotech-a^al Laboratory, Tokyo, Japan

W ave length in m/u Tr an s mi t tance

400 0.917

410 .914

420 .909

430 .902

440 .393

450 .882

4o0 . 865

470 .335

480 .793

490 . 7^5

500 .703

510 .652

520 .606

530 .571

540 . 575-

550 .615

5b0 .636

570 .594

580 .513

590 .451

6no .454

610 .470

620 .'+79

630 .474

640 .466

650 M3

660 .506

670 .569

680 .665

690 .764

700 .840

710 .883

720 .903

730 .912

740 .917

750 .919