Just to make it clear.
The J-16 does have a HMD (helmet mounted display) which is the picture that Deino posted in reply 889. That design is a monocular HMD where the image is projected onto the visor over the right eye.
The helmet in reply 880 is NOT a HMD.
Most importantly -- for all PLA fighters where pilots have HMDs (including J-20, J-16 and J-10C), they do not fly every single sortie with a HMD, and for missions or sorties where a HMD may not be required, they fly with regular flight helmets instead.
(This is ignoring older and more primitive helmet mounted sights on imported Russian Flankers)
Being able to recognize on sight the HMDs that J-20, J-16 and J-10C use is probably something helpful to learn for everyone.