Power Claims of Convoy Type Flashlights

2.5.2015

 

A pet peeve of mine is honesty in advertising.  Over the past 3+ months I’ve seen companies advertising ever higher power Convoy type flashlights – usually with an LG LED. Every single one of these ads is misleading – I could say downright lies but my bet is that the folks doing so really just don’t understand how an LED works.


Although the LG LED used in the Convoy can be driven as high as 6.6 watts, none really are (except for perhaps a few short minutes with a freshly, hand-picked, battery.  Most of these LEDs require 3.9v to 4.2v to operate at full output.  The 18650 batteries we use rarely can be charged to 4.2v; most will be 4.1v at full charge (and that tenth of a volt *really* matters).  What’s worse, they all quickly discharge below 3,9v in a matter of minutes.  Once below that voltage, the “driver ratings” most manufacturers  claim go out the window.  The driver is not even functioning; it is bypassed and the LED is driven as hard as possible at the lower battery voltages.  DOES NOT MATTER HOW MANY “7135 DRIVERS” ARE USED.  Does not matter what current the manufacturer claims.  Does not matter what wattage the manufacturer claims.  The LED and the battery will make that decision, and it is dramatically lower than the advertised power claims.

 

 

Stop motion video of UVA radiant output of a 6w "Convoy" type light as the battery discharges
over one hour period

 

I realize this is very techy (the reason manufacturers can make these claims without rebuke).  Trust me – you are wasting your money if you pay more for a “6-Watt Convoy” vs. a “4-Watt Convoy” etc. etc. etc.  Some might say that one flashlight is brighter than the other – that all depends on how freshly charged the battery is (in both lights being compared), how good the batteries are, and the variation in the LEDs (they are quite variable), variations in reflectors and filters.  But in reality, after 5 minutes, they are all equal.


So unless you want to be changing your battery every five minutes to insure a high enough voltage, ignore power claims – they mean nothing.
(Note: Flashlights can be designed with the proper drivers and batteries that will drive an LG LED at its full rating.  The Convoy is not.)

 

Voltage/Current Analogy (a tutorial for those who want to understand a little better)
(https://learn.sparkfun.com/tutorials/voltage-current-resistance-and-ohms-law/voltage)

When describing voltage and current, a common analogy is a water tank. In this analogy, charge is represented by the water amount, voltage is represented by the water pressure, and current is represented by the water flow. So for this analogy, remember:

  • Water = Charge

  • Pressure = Voltage

  • Flow = Current

Consider a water tank at a certain height above the ground. At the bottom of this tank there is a hose.  The pressure at the end of the hose can represent voltage. The water in the tank represents charge. The more water in the tank, the higher the charge, the more pressure is measured at the end of the hose.

We can think of this tank as a battery, a place where we store a certain amount of energy and then release it. If we drain our tank a certain amount, the pressure created at the end of the hose goes down. We can think of this as decreasing voltage, like when a flashlight gets dimmer as the batteries run down. There is also a decrease in the amount of water that will flow through the hose - less pressure means less water (current) is flowing.

 

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