[BC] LCD monitors & HV

[RichardBJohnson at comcast.net]

Fluorescent backlights have high-voltage until they light. Then they have about 38 volts, i.e., the ionization potential of mercury vapor at its internal pressure within the lamp. http://www.standnes.no/chemix/periodictable/ionization-potential-table.htm

Older fluorescent lights used a starter that connected the filaments in series with a current-limiting reactor. In a second or two, the starter would open and the inductive kick-back would start the internal gas ionization. The lamp would then have only about 38 volts across it, current limited by the reactor.

Modern fluorescent starters use a resonant circuit at a high switch-frequency to generate the initial spark. Then the current is limited by the inductive reactance of the much-smaller inductor, small because the frequency is high. 

Cheers,
Richard B. Johnson
Book: http://www.AbominableFirebug.com/

----- Original Message -----
From: "Broadcast List USER" <Broadcast at fetrow.org>

Fluorescent backlights have high Voltage.

LED backlights do not.

--chip