While miniature color video cameras are capable of functioning in relatively low light levels (2.5 - 5 lux), the long, narrow aperture of the VO rod endoscope restricts both source and reflected otoscopic image light. Consequently, there is a need for a relatively high intensity light which does not generate heat at the viewing point. The source light for most VO systems is produced by a remote, fan-cooled quartz halogen bulb, of the type found in 35 mm slide projectors or by a metal halide / arc type lamp (Grason-Stadler). The latter light source produces an illumination spectrum more like daylight (color temperature ~5500o Kelvin) while the former spectrum (color temperature ~3400o K.) is consistent with indoor tungsten photographic lighting. If a video camera is adjusted for other than the correct source light color temperature, the video otoscope image will appear chromatically biased toward the red or blue ends of the visible light spectrum, respectively.
Fortunately, all quality VO camera systems have a white balance feature which allows the user to color-correct the image, regardless of the type of source light. Most VO light sources contain a control to vary the illumination level. The light is then transmitted via a flexible fiber optic cable to the VO head, essentially without heat.
The fiber optic cable in VO is used for source light transmission only, unlike flexible endoscopes, such as laryngoscopes and laparoscopes, which carry coaxially both source light and images. The flexible fiber optic concentrates and transmits the high intensity source light with no loss due to scattering. There is essentially no heat / infra-red transmission from the remote light source to the video oto-endoscopic head. Portable VO systems with light source on-board the VO head constellation can generate a significant thermal component with prolonged viewing. Roy F. Sullivan, Ph.D.