Kestrel 4000 Instruction Manual page 9

Backlight
The Kestrel Meter has a high-visibility green backlight, which makes the display easily read in low-light
conditions. The Kestrel 3500 NV has a night-vision preserving backlight which helps users to sustain natural
night vision. The NV's backlight incorporates an optical filter to reduce overall brightness and minimize
blue and green spectrum light to preserve night vision. Additionally, the backlight is much dimmer than a
standard backlight, making it more difficult to detect with the naked eye in night operations. This backlight
appears soft greyish pink (not red) and is still in the visible spectrum, so it is not compatible with night-
vision equipment.
It takes 30 to 45 minutes for the average eye to adapt to darkness and maximize night vision. Even a short
burst of white, yellow, green or blue light "bleaches out" the rod cell photoreceptors in the eye and causes
night blindness until the entire adaptation process can take place again. Light in the red spectrum does not
cause this "bleaching out", preventing night blindness and night vision fatigue.
Press the button to activate the backlight. The light will remain activated for one minute. Press the
button within one minute to deactivate the light manually.
Relative Humidity
The Kestrel Meter is capable of measuring RH to a high accuracy: +/– 3% RH between 5 and 95%. To ensure
operation within these specifications, please follow these recommendations:
• A void taking measurements in direct sunlight, which will heat the air inside the humidity sensor
enclosure and cause inaccurate readings.
• I f your circumstances force you to expose the Kestrel Meter to a large temperature swing prior to taking
a relative humidity reading (such as when taking a Kestrel Meter stored inside at 70° F outside to a
temperature of 40° F), you will need to take additional steps to ensure that the Kestrel Meter's external
temperature sensor is in thermal equilibrium.
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