In article ,
wrote:

A PMAed part or assembly is one that can be used as a direct replacement
for
the original part or assembly. Whether or not the owner/operator can
legally install a PMAed part depends upon the type of part and whether
its
replacement is within the bounds of allowed owner/operator maintenance as
defined in FAR 43.17(c). However, regardless of whether the PMAed part
is
installed by the owner/operator or an A&P, it requires just a simple
logbook
entry just like any other part replacement.

An STC introduces an alteration that was not covered by the airplane's
original type certificate. Installation of an STCed part or system must
be
accomplished in accordance with the STC. This may be a major or minor
alteration, but as I understand it, it would in any case need to be
signed
off by an A&P, and possibly an AI. In many cases a new weight and
balance
would need to be calculated and recorded.

and the OP wrote:
But I'd be using the Nulites not as a replacement for anything,
but as a new lighting solution. Does that make a difference?
That is, does this mean that a PMA is insufficient, and that an
STC is required?

If the part is not PMA'd for your aircraft, you'll need a different
"basis" for the approval of the installation in your aircraft. This
does not need to be via an STC.

As an example, a digital OAT probe I installed in my cherokee
was PMA'd for certain beechcraft aircraft but not my cherokee.
The installation this digital OAT probe was approved via a 337.

good luck.

--
Bob Noel