There is a real simple solution, just put some tape over the "cat's eyes" on the helmet band and they will not reflect light to give away your position.
Why a "flash bang"? A flashlight/flash bang/flash distraction device would lose most of its effectiveness for bright light distraction in the day time. You would probably have better luck by purchasing an extremely bright flashlight, this would enable you to use it in the day or night.
You could make a flashlight that lights up when you throw it, but it would take some work and you would need a rear push button flashlight. Take a rear push button flashlight (the easier the push button, the better). Get a threaded bolt the size of the push button. Put nuts on the bolt to give it added weight and to help it keep the bolt aligned with the push button. Secure the bolt and nuts with glue or tape to the push button (you can rip off the rubber cover to make it easier). You want the bolt and nuts heavier than the flashlight head. This way when you throw the flashlight it will right itself in the air and the bolt/nut combination will hit the ground first. This will depress the push button switch and the light will turn on. The bolt/nut adapter will probably pop off after hitting the ground, so you will have to keep re-attaching it.
A reusable flash distraction device is in the works now for law enforcement and the military for non-lethal force encounters.
