Originally Posted by
Richard Cranium
No, of course it does - you either give up run time, or simply don't power the light well.
And no doubt, they both will run from a 6V or more source.......
For the sake of discussion I was referring to luminous watts. But for anyone who cares, if you know anything about modern LEDs then you'll know you'll want or need an LED that draws at least three watts of power. And that - ladies and gents means you'll want some batteries.........
As far as the original thread is concerned - knowing bike lighting "terms" still won't guarantee satisfaction because there is more to the quality of any lighting system than numerical specs. But my experience suggests that if you need to "see" anything for any length of time you'll need a more powerful system. And they are generally six or more volts.
Well you have your terms confused, that's for sure. So, let's go through this shall we...
A 6V battery with only 100mAHr capacity will likely provide less light for a shorter time than a 2.4V battery with a 1000mAHr capacity. The first will have an ENERGY of 0.6WHr while the second will have an energy of 2.4WHr or 4X as much energy! The power supply only needs to provide a voltage to your lamp that's high enough to produce maximum power when the battery is at it's lowest state of charge. In practice, the electronics modulates the output from the battery or power supply so that it provides a constant voltage to the lamp no matter what the battery voltage is.
It likely true that most of the more powerful lights will have a voltage of 6V or more because they will use multiple cells in series. With a typical lithium cell at about 3.6V if you put four in series you'll wind up with over 14V. If, OTH, the lamp, say an LED, requires, say, 3.3V to produce maximum power then the electronics will modulate the output of the battery so that the voltage the LED sees is 3.3V. Doing it this way allows the battery to drop in voltage, as they all do, but keep the voltage to the LED constant. Now if you want the LED to operate at lower power, say medium, then the electronics will modulate the power from the battery so that the LED see's a lower voltage than on high.
It is surprising how many people confuse simple terms. Voltage is not current. Voltage is not power. Voltage is not energy. Here's the relationship:
P = VI and E = Pt
P = power, V = voltage, I = current and t = time
So, the voltage of the battery pack, by itself, is meaningless as is the Ampere*hour rating. But, if you put the two together you get the energy of the battery and that is important. Again, with modern electronics you can take almost any voltage and make almost any voltage you want. You can, for example, take a 1.2V cell and make a supply that outputs hundreds or even thousands of volts from it and you probably have one on your camera.
So, if you need to output 10W for 3 hours you need a battery pack of 30WHrs or more and it doesn't really matter if that is done using a pack of 3.6V and 8333mAHr or a battery of 14.4V and 2083mAHr or a battery of 24V and 1250mAHr or even 1.2V and 25AHr.
One of the big reasons the light makers have switched to LED is that they are more efficient than other light types so you do not need as big a battery pack. There are other advantages, such as being less prone to damage from shock/bumps.
Brian