Fluorescent lamps

Fluorescent lamps are hardly ever used in industrial image processing anymore. Sometimes, however, hall lighting is already available, which is then used at manual workstations or large machine stations. However, for image processing they should always be used with electronic ballast to avoid brightness flicker effects in the image. Another application that still uses neon tubes today is color measurement applications that use D55 or D65 standard light tubes.

Video: 50 Hz-flickering of fluorescent illumination in slow motion

Typical properties used in industrial machine vision

Functional principle of a fluorescent lamp

Fluorescent lamps are also commonly referred to as "neon light" or fluorescent light. The fluorescent lamp is based on the principle of a low-pressure gas discharge lamp. A noble gas (neon / argon) together with some mercury vapour is ionised by means of an ignition voltage. In this way, the mixture becomes electrically conductive, a high-energy low-pressure plasma is generated.

This possibility to generate light is based on electron transitions within the atomic structures of the gas mixture. Exited electrons pass over from higher energy levels to lower ones and in doing so they emit mainly ultraviolet light. Because of the very discrete atomic transitions rather narrow-banded emission spectra are typical for gas vapour discharge lamps.

In order to generate visible daylight, the tube is coated with fluorescent substances (= luminescent material) on the inside.

These coatings absorb the unwanted UV light and emit different colours, depending on the gas filling of the tube and the coating. The tubes are available commercially in different shades of white (e.g. warm white, neutral white, daylight white, etc.). ustrial image processing. LEDs are much more practical here.