UV irradiation is a common method of disinfection, but the UV lampscurrently installed in medical facilities vary in size and are not used in a standardized manner. In order to understand the performance of 20W UV disinfection lampsand to properly use 20W UV lamps, a systematic measurement of clinically used disinfection lamps was conducted in analysis.
1)Lamp qualification standards
According to GB 19258, the new 20 W double-ended UVC germicidal lamp illumination is 1 m distance under the rated value of 75μW/cm². The initial irradiance of the new lamp should not be less than 93% of the rated value. Therefore, the initial intensity of a new 20 W lamp should be no less than 75 × 93% = 69.75 μW/cm². According to the 2002 version of the Disinfection Technical Specification, when the irradiation intensity of the UV lampis reduced to less than 70% of the original intensity of the new lamp, it should be replaced in time. The lamp should be replaced in time. Therefore, the irradiance of a 20W UV lamp in normal use at a distance of 1 m should be at least 69.75 × 70% = 48.825μW/cm² to be qualified.
2) Selection of UV lamps
Firstly, 20 new unopened 20 W UV lamps were randomly selected to determine the irradiance qualification rate of the new lamps. Secondly, from June 2013 to March 2014, 45 of the 245 20W UV lamps in use were selected to calculate the average hourly irradiance decay and thus the service life. 45 UV lamps were selected to meet the following requirements: First, the first measurement of irradiance ≥ 55 μW/cm². Secondly, the lamps should be used in strict accordance with the 2002 edition of the Disinfection Technical Specification after the start of the test, and be able to ensure that the lamps are turned on regularly for 1 h per day. Every 90 h of lamp use was measured in three phases. In addition, of the 245 20 W UV lamps in use at the hospital, five 1 m distance lamps were identified. The 20 W lamps with an irradiance of 49 μW/cm² (the critical value) were used for the germicidal test.
3) Monitoring methods
The monitoring methods were standardized according to the standardized monitoring methods provided by the expert group of Beijing Hospital Infection Quality Control and Improvement Center. The SUV – 3 ultraviolet irradiance meters of China Academy of Metrology were used for measurement. The irradiometer was calibrated annually by the Beijing Institute of Metrology and Inspection Science. The intensity of UV irradiation was measured according to the 2002 edition of the Ministry of Health’s “Disinfection Technical Specification” and the instructions for use of the irradiometer. The UV irradiation intensity was determined according to the Ministry of Health’s 2002 edition of the Technical Specifications for Disinfection and the instructions for the irradiator. Each lamp was measured three times and the average value was taken.
4) Calculation method
The irradiation intensity of the UV lamp gradually decreases during the use of the lamp. It is assumed that the irradiance of the 20 W UV lamp decreases at a uniform rate with the use time. After each 90 h interval of use, a total of 4 measurements were made and the difference in irradiance was calculated. The difference in irradiance is then divided by the corresponding time to obtain the average hourly irradiance decay value. The average irradiance decay time of the new lamp to 48.825 μW/cm² is calculated as the average service life of the 20W UV lamp. The formula is as follows:
Difference in irradiance decay (μW/cm²) = irradiance value 1 – irradiance value 2
Average hourly decay rate (μW/cm²) = Difference in irradiance decay ÷ Corresponding cumulative use time
Average service life (h) = (average irradiance of the new lamp – 48. 825) ÷ average use time 48.825) ÷ Average hourly decay rate
5) Sterilization test
Petri dishes of 90 mm in diameter were used, and bacteria were selected from the standard strain of Staphylococcus aureus (ATCC 25923). Staphylococcus aureus standard strain (ATCC 25923) was used. Firstly, The bacterial suspension was prepared with 2 maximal turbidities, and the bacteria were collected with a sterile quantitative spiking gun. The bacteria were collected with a sterile dosing gun, and 20 μl of the suspension was inoculated on a 90 mm plain nutrient dish. The number of bacteria was 1. 2 × 107 cfu/dish. Each test, A negative control dish was set up. After irradiation, the dishes were placed in a 35 C temperature chamber and the results were observed after 48 h. The results were observed after 48 h.
1) The irradiation intensity of the new 20W UV lamp
According to the standard of initial intensity value of 69.75μW/cm², the qualified rate of irradiation intensity measured by 20 new unused lamps is 90%.
2) Average life span of clinically used UV lamps
Forty-five of the 245 20 W UV lamps in use in the hospital were selected, and the initial intensity ratios of the 45 UV lamps are shown in Table 1. 45 UV lamps were measured in three stages for each 90 h of use. The average lifetime of 20 W UV lamps in our hospital was calculated to be 1,463 h. The average attenuation values of each stage are shown in Table 2.
Table 1 Intensity distribution of the tested 20 W UV lamps
Lamp intensity (W)
Number of lamps
Composition ratio ( % )
55 ～ 60
60. 1 ～ 65
65. 1 ～ 70
70. 1 ～ 75
Table 2 Average irradiance attenuation values per phase and service life
Time of use
Average hourly attenuation (μW/cm²)
3）Critical UV lamp direct irradiation sterilization test
A 20 W UVC lamp (49 μW/cm² at a distance of 1 m) was used to directly irradiate a 9 cm dish inoculated with a standard strain of S. aureus at a distance of 1 m for 43 min, which was able to sterilize 100% of the standard strain of S. aureus at 1. 2 × 107 cfu/dish.
According to the GB 19258 standard, the initial intensity value of a new 20 W UVC germicidal lamp at a distance of 1 m should be no less than 69.75μW/cm². Under this standard, we measured a 90% pass rate for the 20 new tubes. However, in actual clinical use, the irradiance of new lamps can be reduced by the current stability of the output, transformer type mismatch, transformer aging, voltage stability, and other factors. Therefore, the first measurement of 20 W UV disinfection lamp new lamp, intensity ≥ 60 μW/cm² is qualified. According to this standard, we sampled 20 new UV lamps that can all be used normally.
The intensity of 20 W UV disinfection lamps reduced to 70% of the intensity of the new lamp is 48.825 μW/cm², so the standard for 20 W UV lamps in use should be set at ≥ 48.8 μW/cm². The average service life of the 45 UV lamps measured was 1463 h, which is longer than the reported average service life of 30 W UV lamps1 138 h.
The intensity of 20 W UV lamps in use should be measured every six months in daily clinical practice. The lamp should be replaced immediately when the intensity is measured to be less than 48.8 μW/cm². The average lifetime of 1,463 h suggests that the frequency of monitoring should be increased after 1,000 h of use of the 20 W lamp in order not to affect the sterilization effect.
The germicidal effect of UVC is determined by the dose of irradiation received by the microorganisms. Dose = irradiation time (s) × intensity (μW/cm²). The higher the irradiation dose, the higher the disinfection efficiency. Therefore, the use of 20 W UV lamps for disinfection of the medical environment should be in accordance with the Technical Specification for Disinfection of Medical Institutions, which states that the lamp should be suspended at a height of 1.8 m to 2.2 m from the ground, with an intensity of ≥ 1.5 W/m² and an irradiation time of ≥ 30 min. The cleanliness of the UV lamp surface impacts the disinfection effect, and the UV lamp should be wiped regularly with alcohol for a comprehensive wipe. If the number of UV lamps is insufficient, you can measure the irradiance value and then calculate the length of irradiation according to the formula, by extending the irradiation time can achieve the same sterilization effect.