A restricted class of OTC drugs also exists in the U.S. This restricted class includes drugs such as pseudoephedrine, emergency contraception, and some Schedule V controlled substances. These products, while considered OTC, are kept behind the pharmacy counter and must be dispensed by a pharmacist pursuant to proper identification, age verification, and patient education.
The lux (symbol: lx) is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface.
This quantity is measured in terms of the power emitted per unit solid angle from an isotropic radiator, a theoretical point source that radiates equally in all directions in three-dimensional space. The standard unit of luminous flux is the lumen (lm). Reduced to base units in the International System of Units (SI), 1 lm is equivalent to 1 candela steradian (cd Â· sr). This is the same as 1.46 milliwatt (1.46 x 10 -3 W) of radiant power at a wavelength of 555 nm, which lies in the middle of the visible spectrum. Compare radiant intensity. Also see electromagnetic field, lumen, International System of Units (SI), and Table of Physical Units.