Nik Collection

Lightroom Desktop added the ability to configure 3rd party editors in the October Release

Right-click on an image, choose Edit In and browse to your Nik executable.  Once you do this, it will appear in Edit in as an Option. 

(I have no recent experience with current NIK apps. Following is how the earlier NIK versions worked! )

Lightroom-Desktop does not allow the use of Plugins, but you can use the NIK apps in several ways.

1) Select an image and go FILE > Edit in > BROWSE  (to the Nik App/feature you want in Applications. Windows users would browse for the .exe app file.)

2) Select an image and [Edit in Photoshop],

Convert the background layer to a Smart Object

Apply a NIK filter  eg. FILTER > NIK Collection > Silver Efex

Make adjustments to the image in NIK and [Save]

* *This method has the great advantage that the NIK adjustments are preserved in the Photoshop TIF file as a Smart Filter that can always be re-opened and the NIK settings (in the Smart Filter) changed as desired.

3) Export an image from the Lightroom-Desktop Library to a local drive

Start the wanted NIK app (as independent app)

Open the exported image with the NIK app, FILE > Open Images...

(In Windows I can [Open With] and choose a NIK app.)

Save the edited image from Nik, and IMPORT the new file to Lightroom-Desktop.