EC1-L

The Hagner EC1-L is a compact instrument for measuring the luminance of luminous screens, for instance of film and slide viewers, X-ray viewers etc., and for easy calculation of film density. It has both an automatic zeroing and an on/off switch and the only controls needed are a four position range selection switch and a hold button to retain the displayed value.
The opening of the detector, which should be pressed against the screens, has a round aperture with an area of 1 cm².
The meter is calibrated to read 1 cd/m² to 2,000,000 cd/m² in four measurement ranges. The L model calibration is suitable for X-ray viewers
The calculation of film density requires also a simple calculator which will give the logarithm to base 10 of a number (LOG10).

A. Measure the luminance (Ls) of the blank viewing screen and enter into the calculator.
B. Measure the luminance (Lf) of the film when placed over the screen.

Ls
-----
Lf

Film density is then given by D = LOG10

Screen luminance is 1,352,000 cd/m2
Film luminance is 107.2 cd/m2

1,352,000
------------- = 4.1
107.2

Density is D = LOG10

If the value of screen luminance is stored in the memory of the calculator, the density at several different positions on the film can be calculated very easily.