There is a second plug on the back of the unit that needs to be plugged in to power the light, ensure this is inserted.
The light can be turned off with a small, white, touch sensitive button on the top right corner of the front of the Riley. Press this to cycle through 4 different settings: Bright, Brighter, Brightest, and Off. Make sure it isn't simply set to "Off". Sometimes this button can be a bit tricky to press, so make sure you press all around it as well to make sure you're getting it.
If this still doesn't work, we may need to organise a replacement power adapter for you, get in touch to organise this.