11-4 Reflectance

11-4.1 Overview

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

 

Decimals

Fractions

#/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).