Claimed run time difference at ~120 lumens, JetBeam BC-40 vs Balder BD-2

maunaloa

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My first post after lurking a long time. Thanks for the great forum, and esp. to selfbuilt for the incredibly detailed and photographed reviews!

I'm puzzled by the different run-times at 120 lumens claimed in the product specs of the JetBeam BC-40 (2x19670) vs. a Balder BD-2 (1x19670):
BC-40: 11 hrs @ 130 lumens (low setting)
BD-2: 10 hrs @ 120 lumens (medium setting)

Given that the BC-40 has twice the mAh, I would expect about twice the run time, discounted by ~8% for the 10 additional lumens. What gives?

Also, the color temperature of my BD-2, Fenix TK-35, and Nitecore TM-11 are a nice neutral white, but the BC-40 is much warmer.
http://www.cree.com/products/xlamp_xml.asp
Could the BC-40 be an "XL-M Warm"?

Do any manufacturers disclose which of the three color temps are used?

Does Cree offer the three color temps in all Group Codes?
 

AnAppleSnail

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I'm puzzled by the different run-times at 120 lumens claimed in the product specs of the JetBeam BC-40 (2x19670) vs. a Balder BD-2 (1x19670):
BC-40: 11 hrs @ 130 lumens (low setting)
BD-2: 10 hrs @ 120 lumens (medium setting)

Given that the BC-40 has twice the mAh, I would expect about twice the run time, discounted by ~8% for the 10 additional lumens. What gives?
Depends on the regulation. Find a "runtime chart" for these lights to see if they hold 120 lumens for the whole time, or if they drop off gradually. Many lights do the first for light nuts who want every lumen. Others do the second for light nuts who value runtime over lumen count.

Tint is variable; some manufacturers disclose the LED tint, but it's rare - sometimes suppliers won't ship them what they want, other times the tint bins are wide enough to fit a zebra-stripe truck through.
 

PCC

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There are a lot of different things to consider, here. Manufacturer's specs are inconsistent from manufacturer to manufacturer because they don't need to follow any standards. If you have two hypothetical identical lights from two different companies you might get two different sets of performance specs even if they sourced the identical light from the same manufacturer. Why? One might give you an inflated high output rating based on a perfect example of the emitter in the light driven at spec while the other gives you an actual number obtained from testing the light in a sphere. For run times, you might get numbers for how long it runs until it reaches some percentage point, or completely dead, or some lumen value, all of which will give you different run times.

The only numbers that you can reliably compare would be the numbers from the same manufacturer or from the same reviewer (for example, only compare Selfbuilt's review numbers to his other review numbers, don't compare his numbers to someone else's as the testing procedures are different as well as their thresholds). Even then the numbers can be off a bit depending on a lot of factors: age of the cells, temperature, calibration of the testing equipment, etc.

What it boils down to is that you should buy a light based on the physical aspects of it (fit, finish, warranty, etc) and not so much on the performance specs. Sure, the output is important to know, but, you won't know how it will perform for you in real world use until you put it through its paces. That's why people seemingly buy then sell their lights: they're looking for the perfect light for them.
 

maunaloa

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Thanks for the replies. I had overlooked the importance of each manufacturer's approach to regulation. Does CREE provide a "template design" for regulation circuits used with its LEDs, or is the design completely in the hands of the flashlight designer?
 
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Kokopelli

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Of course just the decision of the light's manufacturer. Cree can't guess your power source and it's chemistry. Although lithium ions and primaries usually have a flat discharge regime compared to alkalines, for a single li-ion cell, voltage gradually drops from 4.2v to 3v during its discharge. With a dual cell setup a buck circuit is needed, and it's behavior can be set by clever manufacturers accounting the left runtime, the overall temperature and flat regulation. For single cell lights, you may use boost circuits to maintain a set current, or let it drop gradually, or with nice steps like as in an Armytek Predator.

Just a side note, MagLeds give their max lumens at the first minute after turning it on, then the light level drops to 50% after just a few minutes. So you don't always get Xx lumens for Yy time but you get a max of XX lm, and a max runtime to the level down to 10% of X lms, and call this the useable period. Some give the tactical runtimes also, to the point down to 50% X brightness, whose usually are like a quarter or half of the useable runtimes given.
 
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