Knowledge Base

General

Generally, for optimal tracking it is important that the contrast between the subject and the background is as good as possible. For marker tracking, EthoVision XT needs to be able to distinguish the different marker colors. For both issues, the lighting conditions play an important role.

• It must be bright enough. A low light intensity can result in a suboptimal contrast between the animal and the background and therefore tracking might not be optimal. Furthermore, a low light intensity makes it difficult to separate different colors. When it is not possible to use strong illumination in your setup, try using fluorescent marker colors with UV lighting.
• It must be even. The light source should be diffuse, for example, a shaded fluorescent tube or globe-type incandescent bulbs. This way, the contrast between the animal and the subject and the intensity of the marker color are the same throughout the arena.
• Shadows must be avoided. To avoid shadows, do not point the light directly to your animals, but, for example to the walls or ceiling. Use several lamps, to obtain an even illumination.

Full-Spectrum Lights

For optimal color separation, illuminate your setup with lamps that approximate to day-light in frequency distribution of wavelengths, that is, have a full-spectrum range. There is no technical definition of "Full spectrum", therefore it cannot be measured. However, to compare full-spectrum lights you can directly compare spectral distributions.

In practice, full-spectrum lights can be recognized from two parameters:

• High Color Temperature (measured in degrees Kelvin). Usually higher than 5000 ºK. Values of color temperature around 2500–3000 ºK are typical of "warm" color lights (yellowish), for example incandescent bulbs.
• High Color Rendering Index (expressed as percentage). Higher than 95. A value of 100 represents the ideal or natural light.

See also:

• For color temperature: http://en.wikipedia.org/wiki/Color_temperature
• For color rendering index: http://en.wikipedia.org/wiki/Color_Rendering_Index

When buying LED lamps, make sure that the technical specifications report the required color temperature and CRI. A disadvantage of most LED lamps is that they cast light in one direction at a narrow angle compared to energy-saving fluorescent lights, creating more shadows and reflections.

We have tested the following lamps:

• True-Light Energy Saving Light 15 W. Color Temperature 5500 ºK, Power 15 W, Brightness 720 lumen.
• ProLite Helix Compact Fluorescent ES 15. Color Temperature 6400 ºK, Power 15 W, Brightness 795 lumen.

Both lamps have E27 fitting.

Recommendations

• Choose a light source with color temperature ≥ 5500 °K and color rendering index > 95.
• Do not use halogen lamps; instead use LEDs, as halogen light is too "cold".
• Use at least four lights and place them at equal distance around the arena, at least 1 m from the subjects.
• If the image of white animals looks overexposed, close the aperture of the camera lens. Too much light heavily reduces color discrimination.
• If light creates shadows in the arena, place white sheets in front of the lamps to obtain more diffuse light.
• Set the white balance of your camera, to obtain a wider color spectrum. Consult the manual of your camera for the exact procedure. Generally, you can set the camera to white balance the image automatically. To check whether this is done correctly, point the camera to a white wall and check whether the wall appears white in the video image. If this is not the case, search for the settings to set the white balance manually. Point the camera to a white wall and set the white balance. Make sure you do this every time the light changes.

Useful Web Sites

Below you find the web addresses of full-spectrum light producers:

• True-Light: http://www.true-light.eu/en/
• BlueMax Lighting: https://www.fullspectrumsolutions.com
• OSRAM: http://www.osram.com/
• Philips: https://www.lighting.philips.com/main/home
• Pro-Lite: http://www.prolite-lamps.co.uk
• Viva-Lite: http://www.viva-lite.nl/home.html

Source: EthoVision XT 19 Help, Noldus Information Technology