An optical filters can be described by its shade number, which correlates with its transmittance of radiation. It describes the protection offered by the filter to intense light.
Examples: welder's glass
|
Shade Number |
Maximum Luminous Trans-mittance |
Standard (Nominal) Luminous Trans-mittance |
Maximum Effective Far UV Average Trans-mittance |
Maximum Infrared Average Trans-mittance |
|
Clear (0) |
100% |
NA |
NA |
NA |
|
1.5 |
67% |
61.5% |
0.1% |
25% |
|
1.7 |
55% |
50.1% |
0.1% |
20% |
|
2.0 |
43% |
37.3% |
0.1% |
15% |
|
2.5 |
29% |
22.8% |
0.1% |
12% |
|
3 |
18% |
13.9% |
0.07% |
9% |
|
4 |
8.5% |
5.18% |
0.04% |
5% |
|
5 |
3.16% |
1.93% |
0.02% |
2.5% |
|
6 |
1.18% |
0.72% |
0.01% |
1.5% |
|
7 |
0.44% |
0.27% |
0.007% |
1.3% |
|
8 |
0.164% |
0.1% |
0.004% |
1% |
|
9 |
0.061% |
0.037% |
0.002% |
0.8% |
|
10 |
0.023% |
0.0139% |
0.001% |
0.6% |
|
11 |
0.0085% |
0.0052% |
0.0007% |
0.5% |
|
12 |
0.0032% |
0.0019% |
0.0004% |
0.5% |
|
13 |
0.0012% |
0.00072% |
0.0002% |
0.4% |
|
14 |
0.00044% |
0.00027% |
0.0001% |
0.3% |
If the shade number and maximum luminous transmittance are modeled in JMP (excluding the clear shade and starting with 1.5):
LOG10(maximum percent transmittance) =
= (-0.002696 * ((shade number)^2)) - (0.376023 * (shade number)) + 2.4121825
According to the General Occupational Health Standards,
shade number =
= (7 / 3 * (filter density)) + 1
with the filter density = LOG10( 1 / (nominal transmittance as a decimal fraction)), as described in the previous section.
