Head light is a generic Cree XML T6 based bike light, $38 at Amazon and elsewhere. Light straps to helmet using zip ties and some fiddling. Battery straps to rear the same way. Also two red lights on rear.

A helmet light is a very useful thing because you can aim it right at a car whose driver needs to see you. If the light is bright and focused enough, you will almost assuredly get his attention when his cockpit lights up or his mirror flares. Then he has to figure out what you are - reflective clothes, regular headlight/taillight, etc all help there.

I don't find zip ties or straps through the helmet vents to be noticeable. I guess it will depend on how neatly you do the straps and how fussy you are. This time of year, I am wearing a cap under the helmet anyway, for rain protection.