A command line tool for controlling Elgato Key Lights and Key Light Airs.
A library for interacting with the lights yourself is available at endocrimes/keylight-go.
[keylightctl(master)] $ ./bin/keylightctl describe --all
+---+--------------------------+-------------+------------+-------------+
| # | NAME | POWER STATE | BRIGHTNESS | TEMPERATURE |
+---+--------------------------+-------------+------------+-------------+
| 0 | Elgato\ Key\ Light\ 861A | on | 50 | 295 |
+---+--------------------------+-------------+------------+-------------+
[keylightctl(master)] $ ./bin/keylightctl switch --light 861A off
[keylightctl(master)] $ ./bin/keylightctl describe --all
+---+--------------------------+-------------+------------+-------------+
| # | NAME | POWER STATE | BRIGHTNESS | TEMPERATURE |
+---+--------------------------+-------------+------------+-------------+
| 0 | Elgato\ Key\ Light\ 861A | off | 50 | 295 |
+---+--------------------------+-------------+------------+-------------+
[keylightctl(master)] $ ./bin/keylightctl switch --light 861A --brightness 25 on
[keylightctl(master)] $ ./bin/keylightctl describe --all
==> Found no matching lights during discovery
[keylightctl(master)] $ ./bin/keylightctl describe --all
+---+--------------------------+-------------+------------+-------------+
| # | NAME | POWER STATE | BRIGHTNESS | TEMPERATURE |
+---+--------------------------+-------------+------------+-------------+
| 0 | Elgato\ Key\ Light\ 861A | on | 25 | 295 |
+---+--------------------------+-------------+------------+-------------+
[keylightctl(master)] $