I'd heard from a gun press writer(also a working LE officer) a regular white light(also called a flashlight) should be at least 65 luminems(check spelling).
The light should also have the new strobe feature, be Li battery powered(for low temp/cold weather uses), be polymer or durable, have a CREE or LED light source, have a tailcap button(very handy for 2 hand holds w/ a handgun), be waterproof to at least 30ft or so.
S&W had a great M&P light on
www.qmuniforms.com and The Sportsman's Guide had a well made off-brand that could be re-charged for around $35.00 USD. See
www.thesportsmansguide.com
Surefire, Insight and 5.11 had a few good compact white lights too.
Clyde
www.PoliceHQ.com www.Galls.com www.UScav.com