PASCO PS-2149 UVA Light Sensor - Manual (Page 2)

UVA Light Sensor Model No. PS-2149
2 ®
Introduction
The PASCO PS-2149 UVA Light Sensor is
designed for use with a PASCO PASPORT
interface to make measurements of relative
electromagnetic radiation intensity in the UVA
band.
The sensing element of the UVA Light Sensor is
a fairly broad-band Si photodiode. It is sensitive
to electromagnetic energy ranging from visible
light to above the UVA band. Since the radiation
typically measured by the sensor is in the UVA
band, the sensor is furnished with a UVA filter
(UG-1 glass) that blocks light in the visible
spectrum. You can remove the filter to make
broader band measurements.
The Ultraviolet (UV) radiation band extends
from very short wavelengths of 100 nm, just
below the x-ray band, to 400 nm, which is just
above visible violet light. This can be observed
in the table below.
The UV band is divided into four smaller bands
according to the nature of the radiation. The
shortest wavelengths are designated as the
vacuum UV band (
λ = 100–200 nm), so called
because energy in this band can only be studied
in a vacuum. Oxygen and other gas molecules in
air absorb radiation in the vacuum UV band.
The UVC band ranges from 200–280 nm.
Essentially all UVC radiation from the sun is
absorbed or scattered by ozone in the earth’s
upper atmosphere and does not reach the
surface.
UVB radiation ( λ = 280–315 nm) from the sun is
also absorbed or scattered by the upper
atmosphere but under some conditions it can
reach the surface of the earth.
Vacuum UV, UVC and UVB radiation have
harmful, high-energy photons and can initiate
chemical processes including changes in
biological tissue called photo-biological
reactions. Reaction-causing UV is also called
actinic ultraviolet. It is characterized by photon
energies above about 4 electron volts (eV). To
compute the photon energy in eV from the
wavelength in nanometers (nm), use this
formula:
For example radiation with a wavelength of 315
nm has a photon energy of
UVA is the least hazardous ultraviolet radiation.
Its band extends from 315–400 nm.
It is worth noting that ordinary glass cuts off UV
radiation with wavelengths of less than about
300 nm. Thus UVA and some UVB can pass
through glass.
Optional Accessories Model Number
UVA Light Sensor Accessory Kit CI-9792
365nm Filter Accessory CI-9841
PASPORT Extension Cable PS-2500
Ultraviolet Band ( λ = 100–400 nm)
vacuum UV UVC UVB UVA
100–200 nm 200–280 nm 280–315 nm 315–400 nm
far UV near UV
E
1240 eV nm ⋅
λ
------------------------------- .
=
E
1240 eV nm ⋅
315 nm
------------------------------- 3.9 eV. ≈
=