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Measurement and Evaluation of the Safety of UV Light Sources|Part4: The Ultraviolet Mercury Lamp Safety Analysis

The peak wavelength of the uv mercury lamp is 254nm, with short spectrum line and strong power, it is mainly used for sterilization. The UV mercury lamp is placed in the UV radiation box to measure the UV spectral irradiance distribution.

Measuring Condition: light receiving head is 1 meter away from the center of the light source. The tube current is 0.297A, the tube voltage is 102V, and the power is 29.2W.

Measuring result: the spectrum radiation distribution is shown as figure 3.

Illuminance: 30.94 lx;Irradiance: 89.21uW/cm2
54 nm effective radiation intensity of illumination for sterilization: 63.374uW/cm
Effective radiation illumination of photochemical harm to skin and eyes: 31.9318uW/cm2
Effective radiation illumination of near UV harm to eyes: 3.5935uW/cm2

Since the spectrum radiation illumination distribution is fixed when the UV mercury lamp is under the normal work, each weighing function V(λ)、SUV (λ) is also fixed, the rate of the effective irradiance and the illuminance (Luminance Meter) is the constant. Therefore, as long as we control the illuminance in a certain range, we can control all kinds of harmful effective radiation illumination. We can get the following conclusion:

a)Photochemical harm to skin and eye

formula 3

b) Near UV harm to the eye

From formula (2a) (2b), we can get:

formula 4

Note: E in the above formula (3)、(4) and figure 4 represents the light illumination, formula (5)、(6) in the following two figures is the same with figure 6.

UV mercury light spectrum distribution

Figure3: UV mercury light spectrum distribution

UV mercury light safety evaluation curve

Figure4: UV mercury light safety evaluation curve

From the above formula, we can draw up the safety evaluation curve, as shown in figure 4(since the light curve illumination value difference is huge, we take illuminance as logarithm form, as shown in figure 6.

a) In order to avoid the harm of the two kinds of uv light under the UV mercury lamp, the lamp should work in the public areas below the two curves (figure 4 is the area between the photochemical harm appraisal curve and the Irradiation time coordinate).

b) The possibility of causing eyes near uv harm by uv mercury is less than the skin and eyes photochemical hazards. The reason is that the wave band 315~400nm spectral irradiance caused by the eye near uv harm is rather small (as shown in figure 3).

c) Example: In order to prevent the uv harm, when human body irradiation time is 1000s, the light illumination of the human body illuminating area should be controlled less than 2.9068lx, then the maximum illumination of 254 nm effective radiation sterilization is 5.954 uW/cm2. If we use the lamp under the illuminance of 10lx, the time for people receiving the illumination is less than 290.68s, at the same time, the illumination of 254 nm effective radiation sterilization is 20.48 uW/cm2.

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