Creating a set of spotlights on one dimmer switch I'm hoping this is a really easy one for someone to answer and I'll be totally fine with discovering something's been staring me in the face.

Question: How do I adjust, say, the energy or colour of six spotlight lamps at once.

What I'm trying to do: I've created a set of six spotlights washing a couple of walls. Each spotlight is rotated in a slightly different direction. I'm now at the stage where I'm trying to fine tune the lighting effects I've got.

How I got here: I created them by using Shift+D - was this my mistake?

The wild geese I've chased: If I select all six of the spotlights, only the last one takes on the changes. I've tried parenting them and grouping them with no success, so now I'm stumped. I see that 'modifiers' is not available in the properties bar when I have the spotlights selected, and I've scouted about in constraints (as well as searched the internet) - am I warm? 

Thanks for taking the time.
You should copy them with Alt+D, which would mean they are linked duplicates. Then changing the emission value on one would change all them at the same time. This is the solution as long as it's okay for all of them to have exactly the same properties. 

If you need them to differ on some properties, you would need to select them all, change the emit value and then right click on the emit value and select "Copy to Selected" if you just want to update one value on all the selected lamps.