How can I force my keyboard backlight to turn on?

I have a MacBook Pro. When it senses the ambient light is low, the backlit keyboard turns on, and there are keys that let me control its brightness.

But when enough light reaches the ambient light sensor, the backlight turns off and I can't adjust it:

In some settings the screen may be illuminated, but the keyboard is not well-lit and hard to see, so I'd really like the backlight to turn on. Is there any way to force-enable it?

gentmatt’s answer seems useful!

Alternatively, you could try going to System Preferences → Keyboard, and unchecking the “Automatically illuminate keyboard in low light” setting. That should prevent the “disabled” icon from your screenshot altogether.

LabTick allows you to manually control the keyboard backlight: