I’ve carried various Photon lights on my key chain almost since they were first marketed. I currently use a yellow bulb , Photon Freedom , with the cowl over the bulb sides. I perceive more beam projection ( unscientific impression) with the cowl and certainly less distracting side scatter. I chose yellow light based on the info on the Photon site. Yellow seemed the best combo of illumination, battery life and night vision preservation. Check out the descriptions on their website. I avoided red as I live urban. I do not want to be mistaken for a “ shooter” when turning the light on or changing aim point.

NOTE: I carry the Freedom as a backup to my Fenix E05. It serves well in that role. HOWEVER, the push switch is too easily depressed in the pocket, by keys, etc., resulting in a depleted light. So I carry mine on the neck dangler, switch faced in. That prevents accidental “on”.