Equinox Systems Cirrus User Manual page 12

Equinox Cirrus
What types of effect are safe to scan directly at audiences?
Fast moving laser effects with evenly distributed scan patterns, such as circular tunnels are
generally safer than effects such as finger beams, or effects with pronounced bright spots in them. Dif-
fraction grating type effects are typically safer to point towards an audience, as long as the bright central
spots are kept above head height. The important thing is to not guess if an effect is safe or not, and if in
doubt keep it above head height. Being aware of the laser's hazard distance is useful to know.
Hazard Distances
All display lasers have a characteristic known as the hazard distance for direct viewing (NOHD). This is
distance at which the hazard of viewing the laser directly no longer presents a hazard. i.e. at any point
between the laser projector and the calculated hazard distance, it may be hazardous to view the laser
directly. But viewing the laser directly from beyond the hazard distance is
considered to be safe.
The worst case effect to look at directly is a static single beam, because all the light energy is concen-
trated into one point. The hazard distances for several different powers of typical Class 3B laser are
shown in the table below, to give an idea of the distances involved.
Laser Output Power 10mW
Hazard Distance
Table 1 Static Beam Hazard Distances.
Note - The values have been calculated assuming the characteristics of a typical laser lightshow device,
which has a beam spread of 2mradians. Actual devices may differ in practice, so this table should only
be used as a guide. Details of how to calculate laser hazard distances are detailed in the British Safety
Standard, and many laser safety text books. It is also one of the topics usually covered in laser safety
courses.
It can been seen that static laser beams can remain hazardous for considerable distances, which is why
projecting such effects into peoples faces in not recommended.
Remember, projecting these beams overhead is fine, as long as they, or any reflections, are not hitting
anybody.
When an effect such as a tunnel is projected, the continual scanning reduces the time the eye is directly
exposed to the laser energy. These types of effect are less harmful to aim at the audience directly. The
table below shows the hazard distances of a stationary circular tunnel, with a spread of 50 degrees, and
a scan rate of 20Hz, to give an idea of how it is reduced.
Laser Output Power 10mW
Hazard Distance
Table 2 Scanned Tunnel Hazard Distances.
30mW 50mW
12m 20m 25m
30mW 50mW
5m 9m 11m
100mW 250mW
36m 56m
100mW 250mW
16m 26m
Safety
450mW
76m
450mW
35m