If there are sparks there is light. A spark is a very wide band transmitter - it creates just about every single frequency of light possible.

See http://en.wikipedia.org/wiki/Spark_gap_transmitter

I guess I shouldn't have used such a strong word like "causes this" since the article was more about the force field and not the source of the ionized air.

The point is that if the tape spool can create such a strong field then there is more than likely a visible light being created at the interface of the spool and tape caused by the charged atmospheric nitrogen which releases a photon when leaving the excited state.

Photons mediate the electromagnetic force it's very likely there was light involved.