|Table 1. Permitted Tolerant Exposure
Ultraviolet radiation is harmful to the human body, particularly
causing disturbance in the functions of eye & skin.
The degree of irradiation risks varies depending on the wavelength of radiation,
and its details have been clarified today.
As human eyes are most susceptible to ultraviolet radiations, we
consider eyes as the most important organ for us to protect from exposure.
PERMITTED TOLERANT UV EXPOSURE
Table-1 shows a permitted tolerant value of UV exposure for each
wavelength, which we call TLV (Threshold Limit Value) in accordance with
the recommendation given by the ACGIH (the American Conference of Governmental
The most harmful wavelength is 270nm and its value of TLV is the
The figure 1 shows harmful ratio having relevance to the spectrum.
LOW PRESSURE MERCURY LAMP
The main wavelengths of LP Hg lamp are 254nm & 185nm. The summed
energy of both UV ray occupies 90% of the total radiation.The single 254nm
radiation occupies 80% of the total energy. The wavelength of 254nm is
so hazardous as well as a high energy ratio, you have to concentrate your
protection measures only on the 254nm when you handle a low-pressure mercury
HIGH PRESSURE MERCURY LAMP
High pressure mercury lamps irradiate wider range of line spectrum
and continuous wavelength, from UV to infrared. The main wavelength is
365nm. Unlike low pressure mercury lamps the high pressure mercury lamps
have a lower 254nm ratio. In case of SEN Lights HL-100 lamp, only 8% of
whole emission energy is from 253.7 to 276nm ray, but the danger is about
170 times of 315nm, for safety measures, it is rational to use 254nm as
the standard rather than 365nm. High pressure mercury lamp irradiate many
wavelength, hence to calculate the tolerated value, exposure value of each
wavelength must be integrated. Practically, from dangerous point of view,
overall exposure is about twice as that of 254nm, therefore half of tolerated
value makes thing safety.