SEAL 44/62 Ultra Plus Spécifications télécharger pdf (Page 6)

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Mercury Vapor and Metal Halide

Lamp Starting

Both mercury vapor and halide lamps use a separate

starting electrode. This starting electrode is located next

to one of the main electrodes inside the arc tube. The

start-up electrode allows these lamps to be started us-

ing a much lower start-up voltage than required by HPS

lamps.

When a mercury vapor or metal halide lamp is ener-

gized, an electrical field is generated between one of

the main electrodes and the starting electrode next to it.

This causes an emission of electrons that ionize the

argon starting gas. The ionized argon particles create a

diffused argon arc between the two main electrodes of

the lamp (Figure 2).

The heat from this argon arc gradually vaporizes the arc

metals in the arc tube. These ionized arc metal particles

join the arc stream between the two main electrodes.

When a sufficient number of ionized particles join the

arc stream, the resistance between the main electrodes

drops to a point where the start-up voltage supplied by

the ballast can strike a current arc across the main elec-

trodes. The arc current continues to increase until the

current rating of the lamp is reached; a process that

normally takes several minutes.

The HID arc consists of a very rapid flow of both elec-

trons and charged arc metal ions. During this rapid

movement, countless collisions occur between ions and

electrons. As these particles collide, they release en-

ergy at a specific wavelength (Figure 3). This energy

appears to us as light. Because the number of particles

in the arc tube is so great and the occurrence of colli-

sions so frequent, it appears that the entire arc path

constantly generates light.

The color of the light is a characteristic of the light spec-

trum wavelength of the arc metals contained in the arc

tube. For example, in a mercury vapor lamp, the mer-

cury produces a distinct greenish white-blue light. Red,

orange and yellow hues appear grayish.

Figure2. Mercury vapor or metal halide

lamp starting using a starting electrode.

Figure3. Light production in an HID lamp.

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