It depends upon what aspect(s) of translucnecy you are interested in. If you mean transmission like what fraction of incident light (from, say, a hemisphere over a surface) is transmitted through a translucent material, this is a unitless quantity expressed as a percentage or fraction. If you are concerned about the directional scatter of light, then you would measure the bidirectional transmittance distribution function, which would take into account the angle(s) of incident light as well as the angle(s) of the transmitted light. Of course some light from a translucent material will also be reflected back toward the origin of incident light, which is assessed with the bidirectional reflectance distribution function. Further information can be gleaned via Wikipedia at: https://en.wikipedia.org/wiki/Bidirectional_scattering_distribution_function. I guess the units would either be unitless ratios or have some factor like 1/steradians. Lux or candelas would not be relevant since you would need to know the intensity of the incident source, but this is (or should be) independent of the material properties.
Additionally to the very good Answer of John you may also consider the color-rendering. In Germany the Index Ra is used for that. The unit is %.
- Badges
- Science topic