[dfox]

There isn't any ballast to speak of in essentially any LED driver topology, certainly there isn't any inductive component that is used for its reactance as part of the working principle (which is what "ballast" means).

LED driver might have some kind of LC filters on its power input for EMC reasons, but these are too small to meaningfully "sing". On the other hand it may make sense to follow the driver with some kind of reconstruction filter to remove the "high frequency" flicker, but AFAIK nobody does that because it involves costly and large-ish components with significant losses for somewhat questionable benefit.

[sokoloff]

Wouldn’t a boost converter from LiPo to voltage needed to run a string of series LEDs have an inductor? That seems a common design pattern. It’s arguably before the LED driver chip but a meaningful part of the overall design.

Indeed, the Casper uses the Ti TPS63021 boost converter, which needs an inductor (L1/L2 on the datasheet sample application). http://www.ti.com/product/TPS63021?qgpn=tps63021