Use synapse to search in Lubuntu

First install Synapse


sudo add-apt-repository ppa:synapse-core/ppa
sudo apt-get update
sudo apt-get install synapse


Now bind Synapse to the Super_L key alone

First remove any super key bindings e.g. <super>+p is a common one for screen settings

Then close Synapse

In ~/.config/hotkeys/synapse.hotkeys

change

Signature=<Control>space

to

Signature=Super_L

Relaunch Synapse