Chapter 3 Reference Manual
Ranger E/D
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Mounting Rangers and Lightings
3.5.3 Fluorescent tubes
A fluorescent tube illumination has a very uneven spectral distribution, as shown in the
figure below.
Furthermore, there are many different versions with different color temperature and
therefore color balance. Warm white fluorescent tubes typically have color temperatures at
~2700 Kelvin, neutral white 3000 K or 3500 K, cool white 4100 and daylight white in the
range of 5000 K - 6500 K.
In line-scan machine vision applications it is important that the drive frequency of the
fluorescent tube is higher than the scan rate of the camera to avoid flicker in the images.
Fluorescent tubes are light efficient and have low IR content, but they are difficult to focus
to a narrow line. If using IR lasers and the IR pass filter option the white illumination may
cover the same region as the lasers without interference, reducing the focusing problem.
Figure 3.9 – Illustration of spectrum from “yellow” fluorescent tube illumination. [Picture
from Wikipedia.]
3.5.4 White LEDs
LEDs are commonly used in machine vision since they can be focused to different shapes
and give high light power.
White LEDs have a strong blue peak from the main LED and then a wider spectrum from
the phosphorescence giving the white appearance.
This type of illumination is expected to require approximately 60-70% balance on the blue
and green channels compared with the red.
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