Have a look at the picture below. This is a keyboard from a V5. I do not know if all the variants in the V5 range have backlit keyboards but I assume if you find the symbol as shown on the 'F9' key then yours does.
If present, you toggle the light on and off with <FN> + <F9> keys.
It’s time to recognize brummyfan2 for his dedication and collaboration. Please join us in welcoming brummyfan2 to our ACE Team! brummyfan2 has been a valued member of the Acer Community since 2013, eagerly helping users troubleshoot their products.