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6.0 STROBE BRIGHTNESS
The strobe’s brightness depends on how wide the strobe’s flash pulse
is; the wider the pulse, the brighter the flash from the LEDs appears to
be. However, there is a downside to the wider pulses. All strobes work
by giving short bursts of light (the pulse width) at a rapid repetition rate
(the flash 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 flashes
once every 10 msec for a brief moment, the user sees the flash at the
same spot in the rotation of the shaft and the persistence of the eye
remembers this until the next flash making the shaft appeared to be
stopped. As the target is rotating there is some movement evident during
the strobe flash. The longer the flash duration, the more obvious the
rotation is and this increases the blur.
6.1
Calculating Blur
Blur can be calculated – if the shaft is
turning at 6000 RPM, it takes 10 msec to
complete one revolution. If the strobe
flash duration is 100 µsec (1/100 of a
millisecond), the shaft will turn: (flash
duration/time per rotation) x 360°, which is
(.0001/.01) x 360 = 3.6°. So you will see the
shaft appear to move 3.6°.
As the flash 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. The
further away the rotating point is from the
MENU button POWER button On-Target indicator Joystick arrows
MENU button POWER button On-Target indicator Joystick arrows
