Transmittance or
Optical Density?
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Transmissometers measure Percent Transmittance (%T), or in some cases Transmittance (T).

A Transmittance (T) of 1.00 means that for the specific spectral band being measured, all of the light is transmitted.
Likewise a Percent Transmittance (%T)of 100% is an equivalent statement -- all of the light in the spectral band is Transmitted.

Densitometers measure Optical Density.

Optical Density (OD) is defined as the negative logarithm of the Transmittance (T), i.e.  OD = -log(T)

Measurements of Transmittance or %Transmittance are more useful and display more accurately at high Transmittance Levels.

Optical Density is more useful and displays more accurately for low Transmittance as can be seen in the Tables below.

To see comparison between Transmissometers and Densitometers, please click on the link at the left.
 
 

%TRANSMITTANCE (%T)
4-1/2 Digit METER READING
OPTICAL DENSITY (OD)
100.00%
100.00
0.00
 10.00%
10.00
1.00
 1.00%
1.00
2.00
  0.100%
0.10
3.00
0.01%
0.01
4.00
0.001%
0.00?
5.00
0.0001%
0.00?
6.00

 
%Transmittance (%T)
4-1/2 Digit 
Meter Reading
Significant Figures
Optical Density (OD)
4-1/2 Digit 
Meter Reading
Significant Figures
100.00%
100.00
4
0.0000
0.0000
0
99.95%
99.95
4
0.000217
0.0002
1
99.00%
99.90
4
0.004367
0.0043
2
0.010%
0.01
1
2.0000
2.000
4
0.011%
0.01
1
1.9586
1.959
4
 0.012%
0.01
1
1.9208
1.921
4

 
For Further Information, call Gordon Graham today at (818) 700-1263  E-Mail: techinfo@grahamoptical.com
Graham Optical Systems,  9530 Topanga Canyon Blvd.,  Chatsworth, CA 91311
Copyright © 2014 Graham Optical Systems  All Rights Reserved   This page last updated June 9, 2014