Reflectance is the measurement of the light that rebounds from a surface. It is extremely important that the reflectance of the printed address or barcode on a mailpiece contrast sufficiently with the background. The contrast helps to ensure that USPS processing machines can read the address information and direct your mail correctly.
This section provides definitions and formulas for determining the reflectance of mailpiece backgrounds and printing ink, print contrast ratio (PCR), and print reflectance difference (PRD). Values for these parameters are always less than one. Decimals and percentages can express the same amount — for example, 0.65 means the same as 65 percent — and it is easy to convert between decimals and percentages. Use the tables in Exhibit 11-4.1a and Exhibit 11-4.1b as tools to convert between decimals and fractions (USPS standards may appear in either format).
Exhibit 11-4.1a
Decimal and Fractional Equivalents — Fractions Divisible by 32, 16, 8, and 4
Decimals
Fractions
#/32
#/16
#/8
#/4
0.0313
1/32
0.0625
2/32
1/16
0.0938
3/32
0.1250
4/32
2/16
1/8
0.1563
5/32
0.1875
6/32
3/16
0.2188
7/32
0.2500
8/32
4/16
2/8
1/4
0.2813
9/32
0.3125
10/32
5/16
0.3438
11/32
0.3750
12/32
6/16
3/8
0.4063
13/32
0.4375
14/32
7/16
0.4688
15/32
0.5000
16/32
8/16
4/8
2/4
0.5313
17/32
0.5625
18/32
9/16
0.5938
19/32
0.6250
20/32
10/16
5/8
0.6563
21/32
0.6875
22/32
11/16
0.7188
23/32
0.7500
24/32
12/16
6/8
3/4
0.7813
25/32
0.8125
26/32
13/16
0.8438
27/32
0.8750
28/32
14/16
7/8
0.9063
29/32
0.9375
30/32
15/16
0.9688
31/32
Exhibit 11-4.1b
Decimal and Fractional Equivalents — Fractions Divisible by 25 and 5
#/25
#/5
0.0400
1/25
0.0800
2/25
0.1200
3/25
0.1600
4/25
0.2000
5/25
1/5
0.2400
6/25
0.2800
7/25
0.3200
8/25
0.3600
9/25
0.4000
10/25
2/5
0.4400
11/25
0.4800
12/25
0.5200
13/25
0.5600
14/25
0.6000
15/25
3/5
0.6400
16/25
0.6800
17/25
0.7200
18/25
0.7600
19/25
0.8000
20/25
4/5
0.8400
21/25
0.8800
22/25
0.9200
23/25
0.9600
24/25
The symbol “R” indicates reflectance. Only diffuse (scattered) reflectance is of interest. It represents the percentage of incident light diffusely reflected by a material. A surface perfectly reflecting the incident light has a reflectance of 100 percent, and a surface reflecting only half the incident light has a reflectance of 50 percent.
See 11-4.2 and 11-4.3 for information regarding PRD and PRC. Note that mailpiece design analysts can measure PRD and PCR, as well as other mailpiece characteristics, using the Postal Service Envelope Reflectance Meter (ERM III).
