High Pressure Sodium and Metal Halide lamps near plasma ball

AI Thread Summary
Experiments with a plasma globe revealed that a Metal Halide lamp produces a brief white arc that vanishes when the globe is off, while a High Pressure Sodium (HPS) lamp emits a lasting purple glow after the globe is turned off. The persistence of the HPS's purple glow is attributed to phosphorescence, a phenomenon also observed in fluorescent bulbs. Concerns were raised about the risk of the HID lamps exploding without a ballast, but the discussion clarified that the afterglow is a normal characteristic of Sodium lamps. The experiments highlight the unique behaviors of different lamp types in proximity to a plasma ball. Overall, the interaction between HID lamps and plasma globes showcases interesting electrical phenomena.
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I bought one of these plasma globes, decided to do some experiments with it.
Since a fluorescent bulb will light up if It's put near the plasma ball, i tried the same with two HID lamps.

The Metal Halide shows a very pale white arc, which disappears as soon as the plasma ball is turned off...

But the HPS is different, it emits a purple glow, which stays for several seconds after the plasma ball is shut off.

1. Why is this?

2. Also, since the only thing powering those bulbs is the plasma ball, is there any risk of they exploding due to the lack of a ballast?
 
It's phosphoresence and normal for Sodium lamps, also visible in fluorescent lamps to a lesser extent. See the video where the Sodium lamp is turned off around 4:25 and fades to a purple afterglow.
 
Thanks, understood :)
 

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