Four unclued lights are of a kind and the remaining four can be arranged to indicate what unites them.

Across

1               Woman with vintage Italian dress in racecourse (8)

6               Attack mischief maker with plastic gnu (6)

10            Electrical components in versatile robots (12)

11            Almost all wickerwork repelled essential oil (5)

13            Vehicle levy I back, largely, in a roundabout way (7)

14            Ordered Horse & Hound (3,3)

16            Domain name in health app (4)

17            Have no connection with bachelor at first formal (5,3)

23            Keats unsettled after a tea for audience is uncertain (2,5)

25            Resin starts to leak across carpet (3)

28            Meadowsweets in part of church spanning...