Calculating Lumens ??

Calculating Lumens

I know this is a lot more scientific than just shining a flashlight at a meter one yard away. From what I can gather to arrive at an absolute is perhaps beyond most, and most certainly this noob. Still some of you learned flashaholics must of developed some creative systems to arrive at a reasonable guesstimate. What is the foyometer ? what is your process ?

thanks ......... Knobby

Funny you asked, I justed updated my thread:


just make stuff up

ceiling bounce and use your eye on lights of known output

the foy meter changed since he moved ..It used to be based on how long it took to boil water in the pool or set the cactus on fire ..Now i think he is melting a plastic chair .

If you can identify the type of emitter and take a tail cap draw reading in amps you can use this chart to get a fairly close estimate of lumen output.

Match performed extensive testing on the more popular emitters and posted his results in this thread:

I use his data to figure out a torches output based on tailcap draw. Subtract 10-20% for driver inefficiency and 2-5% for lens and you will be pretty darn close to actual OTF lumens. ;)

Hi Johnny, I use that too, but do these formulas work correctly when trying to figure out multiple emitters such as a DRY or Skyray KING etc... Thanks.

It will work if you can figure out how much each emitter is drawing. I can't so I use this

Wow you gotta like that sphere construction, I'll never ceased to be amazed by peoples creative ingenuity. Now to add to my six (yes six) flashlights on order, plus charger/batteries & dmm......... (crikey what have I got myself in to). I think I now need a luxmeter. I had a quick look on the Bay, and yer there cheap, but does anyone have success with one brand over another ?

Thanks ....... Knobby

Sure…I just divide by 3. :wink:

3 cells showing 2.7A draw at the tail is that times the number of batteries. For the DRY it's cell per emitter so 2.7A. For the king let's say it pulls 2A. Multiply by 4 cells and you have 8A. Divide that by 3 emitters and you have 2.67A at each emitter. Do your normal calculations for each emitter then multiply times 3 for total output.

It's actually a lot simpler than it looks written out. :)