Solar Viewing Glasses & Optical Density | Focused Insights

Viewing a solar eclipse can be the experience of a lifetime, but you should only directly view the sun when using approved solar viewing glasses.
Solar viewing glasses reduce the brightness from the sun to safe levels for viewing. In photonics, light reduction is called 'attenuation' and the optical density ("OD") defines by how much.
Optical density is a logarithmic value that represents how many powers of 10, the incident light will be reduced.
To meet safety requirements, solar viewing glasses must meet the ISO 12312-2 standard. The ISO 12312-2 standard defines a maximum transmittance of 0.0032% in the UV and visible ranges (280-780 nm). In the IR(780-2000 nm), the maximum transmittance is much higher, at 3%. These transmittances calculate to minimum optical densities of 4.5 in the UV and visible, and 1.53 in the IR.
While all ISO certified solar viewing glasses should have an ISO stamp on them, this does not guarantee they're certified. Safety viewing glasses should only be purchased from trustworthy suppliers. For approved suppliers, the American Astronomical Society provides a consolidated list. eclipse.aas.or...

[@lidarman2]

Can you measure a high OD with only one detector? Seems most power meters and detectors don't have that kind of dynamic range.

[@thorlabs]

The measurable OD will depend on the optical density, since every detector is limited by its dynamic range. Most standalone photodiode-based power sensors will have an operating dynamic range around 60 dB, so a single detector measurement may be limited to optical densities of ~6.0 or less.
An important consideration for measurement validity is power sensor calibration. Some power sensors are calibrated for 2 ranges by incorporating a switchable ND filter to extend the upper range of the power limit. If the incident power of the source is higher than the sensor’s maximum power without the ND filter, then the measurable dynamic range can be extended. I hope this helps; if you need more specific information, please don't hesitate to contact Tech Support!