Omega Vehicle Security HHLM-2 - Manual (Page 8)

6
SPECIAL CONSIDERATIONS
• Keep the plastic domed cosine corrector clean and free of scratches. It may
be cleaned with a soft cloth and isopropyl alcohol.
• When light is received from many directions simultaneously, take special care
to avoid reflections or shadowing the sensor with your body.
• For best accuracy, repeat the measurement several times to ensure that the
light source has remained stable.
• Avoid flexing the cable excessively at either end of the cable.
• The Inverse-square Law
The law stating that the illuminance E at a point on a surface varies directly with
the intensity I of a point source, and inversely as the square of the distance d
between the source and the point. If the surface at the point is normal to the
direction of the incident light, the law is expressed by E=I/d
2 .
• Cosine Law
The law that the illuminance on any surface varies as the cosine of the angle
of incidence. The angle of incidence
q is the angle between the normal to the
surface and the direction of the incident light. The inverse-square low and the
cosine law can be combined as E=(I cos
q )/d 2 .