A UV light monitoring system, comprising: a processor; and a UV light monitor including a UV sensor, wherein the UV light monitoring system is configured to calculate a UV irradiance on a target surface that is remote from the UV light monitor based on: UV light intensity measurements made by the UV light monitor; a first angle between a normal of the plane of the UV sensor and UV light that is generated by a UV emitter and is incident on the UV sensor; a second angle between a normal of the target surface and UV light generated by the UV emitter that is incident on the target surface; a distance between the UV emitter and the UV sensor; and a distance between the UV emitter and the target surface; wherein the calculation of the UV irradiance on the target surface, I t, uses the equation: I t = I m d m d t 2 cos θ t cos θ m, where I m is a measurement of the irradiance at the UV sensor, d m is the distance between the UV emitter and the UV sensor, d t is the distance between the UV emitter and the target surface, θ m is the first angle, and θ t is the second angle; or wherein the calculation of the UV irradiance of the target surface, I t, uses the equation I t = I m − I A d m d t 2 cos θ t cos θ m, where I A is a measurement of the ambient irradiance measured by the UV sensor. a processor; and a UV light monitor including a UV sensor, wherein the UV light monitoring system is configured to calculate a UV irradiance on a target surface that is remote from the UV light monitor based on: UV light intensity measurements made by the UV light monitor; a first angle between a normal of the plane of the UV sensor and UV light that is generated by a UV emitter and is incident on the UV sensor; a second angle between a normal of the target surface and UV light generated by the UV emitter that is incident on the target surface; a distance between the UV emitter and the UV sensor; and a distance between the UV emitter and the target surface; wherein the calculation of the UV irradiance on the target surface, I t, uses the equation: I t = I m d m d t 2 cos θ t cos θ m, where I m is a measurement of the irradiance at the UV sensor, d m is the distance between the UV emitter and the UV sensor, d t is the distance between the UV emitter and the target surface, θ m is the first angle, and θ t is the second angle; or wherein the calculation of the UV irradiance of the target surface, I t, uses the equation I t = I m − I A d m d t 2 cos θ t cos θ m, where I A is a measurement of the ambient irradiance measured by the UV sensor. UV light intensity measurements made by the UV light monitor; a first angle between a normal of the plane of the UV sensor and UV light that is generated by a UV emitter and is incident on the UV sensor; a second angle between a normal of the target surface and UV light generated by the UV emitter that is incident on the target surface; a distance between the UV emitter and the UV sensor; and a distance between the UV emitter and the target surface; wherein the calculation of the UV irradiance on the target surface, I t, uses the equation: I t = I m d m d t 2 cos θ t cos θ m, where I m is a measurement of the irradiance at the UV sensor, d m is the distance between the UV emitter and the UV sensor, d t is the distance between the UV emitter and the target surface, θ m is the first angle, and θ t is the second angle; or wherein the calculation of the UV irradiance of the target surface, I t, uses the equation I t = I m − I A d m d t 2 cos θ t cos θ m, where I A is a measurement of the ambient irradiance measured by the UV sensor.