optical density (redirected from Absorbance Unit)

optical density

n.

See absorbance.

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density, optical

A term applied to optical filters. It is equal to the logarithm to the base 10 of the reciprocal of the transmission factor T thus,

where D is the symbol for optical density. Syn. absorbance. See absorbance; absorption; spectrophotometer; transmittance.

Table D1 Density of optical lens materials
		n		density (g/cm3)
glass
spectacle crown		1.523		2.54
dense barium crown		1.620		3.71
dense flint		1.706		3.20
dense barium flint		1.700		4.10
titanium oxide		1.701		2.99
plastics
PMMA		1.490		1.19
CR-39		1.498		1.32
polycarbonate		1.586		1.2
cellulose acetate butyrate		1.48		1.2
cellulose propionate		1.46		1.2

Table D2 Relationship between optical density D and light transmission T of optical filters
D	T (%)
0.0	100
0.1	79.4
0.2	63.1
0.3	50.1
0.4	39.8
0.5	31.6
0.6	25.1
0.7	20.0
0.8	15.8
0.9	12.6
1.0	10.0
1.5	3.16
2.0	1.0
2.5	0.32
3.0	0.1
4.0	0.01