Is there a way to set Glow...

...in order to toggle it on and off, preventing the glow afterimage from existing when an object is toggled to be invisible (such as in an "off" state for a neon sign)?

llSetPrimitiveParams([ PRIM_GLOW, ALL_SIDES, 0.0 ]);

If you get an error about PRIM_GLOW not being defined, you are using a viewer in which it hasn't been defined yet. Put the following line at the top of your script, and be ready to comment it out again if you ever compile it and get an error because it has become a built-in constant:

// Just comment this line out if it produces a compile error:
integer PRIM_GLOW = 25;

You may need to change ALL_SIDES to the number of a particular side if it's not for the whole prim. See http://www.lslwiki.net/lslwiki/wakka.php?wakka=llSetPrimitiveParams

llSetPrimitiveParams([ 25, ALL_SIDES, 0.0 ]); // 25 = PRIM_GLOW

This will compile in ANY SL client.

Thank you for your assistance.

Edit: Okay, you can disregard this. Silly me just forgot to set the alpha argument for the color so my script got muddled up parsing the list. :-/

Hmmm I've been trying both
llSetPrimitiveParams([ PRIM_GLOW, ALL_SIDES, 0.0 ]);

and

llSetPrimitiveParams([ 25, ALL_SIDES, 0.0 ]);

and I keep getting a script error:

Hanging Lamp: llSetPrimitiveParams error running rule #2: unknown rule.

(it's rule #2 because in my script the color is being set before the glow.)

Client version is 1.20.15 (92456).

Any ideas?

Do you have the right number of parameters for the color part before that? I've had that before when forgetting to plug in an alpha value.

Was having the same problem and wasn't the viewer version.

Glow worked if in a separate llSetPrimitiveParams call. By making 2 calls it all worked