Monarch Instrument Nova-Strobe PBL - Manual (Page 7)

3
1.2 Brightness
GLOSSARY:
LED – Light Emitting Diode
msec – millisecond = 1/1,000 of a second
µsec – microsecond = 1/1,000,000 of a second
° = degree. One rotation = 360°
The strobe’s brightness depends on how wide the LED fl ash pulse is;
the wider the pulse, the brighter the visual output from the LEDs. Since
the strobe is primarily used on reciprocating or rotating targets there is a
downside to the wider fl ashes. All strobes work by giving short bursts of
light (the pulse width) at a rapid repetition rate (the fl ash rate). Strobes
rely on the persistence of the human eye (the ability to remember and
image) and its response to bright light to give an apparent stop motion
image. Imagine a shaft rotating at 6000 RPM or one rotation every 1/100
of a second (10 msec). If the strobe fl ashes once every 10 msec for a brief
moment, the user sees the fl ash at the same spot in the rotation of the
shaft and the persistence of the eye remembers this until the next fl ash
making the shaft appeared to be stopped. As the target is rotating there
is some movement evident during the strobe fl ash. The longer the fl ash
duration, the more obvious the rotation is and this increases the blur.
This blur can be calculated – if the shaft takes 10 msec to complete
one revolution and the strobe fl ash duration is 100 µsec (1/100 of a
millisecond), the shaft will turn:
(fl ash duration/time per rotation) x 360°, which is (.0001/.01) x 360 = 3.6°.
So you will see the shaft move 3.6°. As the fl ash pulse widens you will
see greater degrees of rotation which results in more blur and a brighter
perceived illumination (the LEDs are on longer so the average light the
eyes see is greater). The trade-off is blur versus brightness. One also has