This is a very diffuse thing!
When talking about artificial light most people report instant light measured by a light meter.
When you se a report about the light in the natural habitat, you very often see very high number, those most often represent maximum amount of light at noon. When the sun is strongest.
The light during the rest of the day can be much lover. As for example, in most tropical rain forests it rains in the afternoon.
What can be said is that for artificial light it is the total amount of light that is interesting. Lover light levels can often be compensated with longer time, to a certain degree. Though there are orchid that really need high light intensities to flower!