Am I Calculating Battery Life and Lumens Correctly?


Newly Enlightened
Jun 17, 2013
So after a few hours of search CPF and Google I surmise that battery life is calculated as such:

Battery Life= Battery Capacity in mAh/(Lamp Wattage/Battery Voltage (Total of all Batteries)=Discharge Rate in Amps)

So in my case, I bought a LED replacement bulb for my Surefire G2Z with a Cree XLamp XP-G which is rated at 4.9W and assuming 2 123's @ 3V each giving me a total of 6V @ 1600 mAh.

That would give me:

Battery Life= 1600mAh/(4.9W/6V=.816A or 816mA)=1.96 hours or 1 hour 57 minutes

My understanding of lumens is this:

Lumens=Bulb Wattage*(Lumens/Watt)

In the case of the bulb I ordered it is 4.9W @ 93lm/W

So I would have 4.9*93= 455.7lm

Do I have this right? If so great, if not some input would be great :thumbsup:


Flashlight Enthusiast
Oct 5, 2010
Hong Kong
You had the driver efficiency, temperature coefficient, battery efficiency/capacity vs current drawn neglected.
The true value of either runtime or output will be lowered
Search any of the flashlight review and take a look at the output-over-time graph and you will have a hint.