Estimation of the Ultraviolet-C Doses from Mercury Lamps and Light-Emitting Diodes Required to Disinfect Surfaces

Abstract

Disinfection of surfaces by ultraviolet-C (UV-C) radiation is gaining importance in diverse applications. However, there is generally no accepted computational procedure to determine the minimum irradiation times and UV-C doses required for reliable and secure disinfection of surfaces. UV-C dose distributions must be comparable for devices presently on the market and future ones, as well as for the diverse surfaces of objects to be disinfected. A mathematical model is presented to estimate irradiance distributions. To this end, the relevant parameters are defined. These parameters are the optical properties of the UV-C light sources, such as wavelength and emitted optical power, as well as electrical features, like radiant efficiency and consumed power. Furthermore, the characteristics and geometry of the irradiated surfaces as well as the positions of the irradiated surfaces in relation to the UV-C light sources are considered. Because mercury (Hg) lamps are competitive with UV-C light-emitting diodes, a comparative analysis between these two light sources based on the simulation results is also discussed.

Keywords: disinfection; dose; dose distribution; light-emitting diodes; modeling; simulation; surface disinfection; ultraviolet-C.

Fig. 1. Diagram of the input and output parameters for modeling the irradiance distribution of Hg lamps.

Fig. 2. Different surfaces within a room are shown receiving different irradiance distributions applied by the same device. It is important to consider the position of the surface relative to the device.

Fig. 3. It is possible to determine the irradiance at any point P by applying a homogeneous cylindrical source and using spherical and rectangular coordinates.

Fig. 4. Left: Rectangular coordinates used to define the position in the x-z plane of the points in the surface that will be used to estimate the value of the irradiance generated by a single lamp. Right: Vector definitions used to compute the rectangular coordinates of any point on the target.

Fig. 4. Left: Rectangular coordinates used to define the position in the x-z plane of the points in the surface that will be used to estimate the value of the irradiance generated by a single lamp. Right: Vector definitions used to compute the rectangular coordinates of any point on the target.

Fig. 5. An SMD UV-C LED is shown in the center of the x-z plane. The detector measures light intensity in polar coordinates for a constant distance from the source.

Fig. 6. Vector relations used to compute the irradiance at any point on the target surface, where the light source is a single SMD UV-C LED (blue box) placed in the x-z plane (source plain) with coordinates (x_M, z_M).

Fig. 7. Rectangular coordinates used to define the position in the x-z plane of the points on the surface that will be used to estimate the value of the irradiance generated by a linear array composed of 10 UV-C LEDs (blue boxes) separated by equal distances at positions on the z axis.

Fig. 8. Irradiance variation depending of the distance for maximum, minimum, and average values for lamp 1. Lamp 1 is described in Table 3.

Fig. 9. Irradiance distribution on the target surface for Hg lamp 1 at 10 cm, 50 cm, and 100 cm, respectively. The black line at 10 cm and 50 cm selects the “homogeneity zone,” respectively.

Fig. 10. Irradiance distribution of central lines in vertical and horizontal directions, applied on a target plane for lamp 1 at 10 cm, 20 cm, 30 cm, 40 cm, and 50 cm. Lamp 1 is described in Table 3.

Fig. 11. Average irradiance distribution and its distance dependence for four different lamps. Lamps are described in Table 3.

Fig. 11. Average irradiance distribution and its distance dependence for four different lamps. Lamps are described in Table 3.

Fig. 12. Dependence of distance and exposure time required to achieve a set value of UV-C dose. Lamps are described in Table 3.

Fig. 13. Irradiance variation depending on the distance for maximum, minimum, and average values for the array with LED 1. LED 1 is described in Table 4.

Fig. 14. Irradiance distribution on the target surface irradiated by the array composed of LED 1 light sources at 10 cm, 50 cm, and 100 cm, respectively. The black line selects the “homogeneity zone,” respectively.

Fig. 15. Irradiance distribution on the target surface for LED 1 at 10 cm, 20 cm, 30 cm, 40 cm, and 50 cm. LED 1 is described in Table 4.

Fig. 15. Irradiance distribution on the target surface for LED 1 at 10 cm, 20 cm, 30 cm, 40 cm, and 50 cm. LED 1 is described in Table 4.

Fig. 16. Average irradiance and its distance dependence for three different LEDs arrays. LEDs are described in Table 4.

Fig. 17. Dependence of distance and time required to achieve a set value of UV-C dose with three different LED arrays. LEDs are described in Table 4.

Fig. 18. Irradiance distribution on the target surface for the LED arrays with 10 LEDs made up by LED 1, LED 2, and LED 3 types, respectively, at the same distance of 10 cm from the target surface. LEDs are described in Table 4.

Fig. 19. Average irradiance depending on the distance for Hg lamp 1 and LED 3.

Fig. 20. Irradiance depending on the distance for comparative analysis between Hg lamp 1 and LED 3.

Fig. 21. Irradiance distribution on the target surface irradiated by Hg lamp1 and an LED array composed of LED 3 at 40 cm.