lights
Lights on handguns were becoming more and more popular about the time I retired. There are many trainers that believe that any defensive/LE firearm NEEDS a light, period, so that threats/non-threats can be positively identified in low light. My own limited experience with the gear indicates I certainly can shoot better with a light on the gun, than juggling light and gun.
One issue not always discussed is the holster. Said holster either needs to: accomodate the pistol and its associated rail, or the railed pistol with the light attached. So there is more to a light on a duty pistol than just issueing the light. The holster needs to accept one or both. Good duty holsters are can be expensive. A good investment, yes, but possibly hard to argue w/ those holding the purse strings if conventional holsters are available/in use, or worse, recently acquired.
If the holster ONLY accepts the railed pistol, sans light, then the light must be dismounted and placed in its own carrier prior reholstering. That is fine for casual use, but if involved in something demanding, as in 'cuffing a suspect, or reholstering before negotiating a barricade, it is more movement and distraction for the officer when he's already mentally occupied and as much an issue as a separate, conventional flashlight, seems to me anyhow.