Originally Posted by
PlanoFuji
Apparently neither your nor the source you cited understand electronics nor basic physics. The dynamo (which provides ALL of the power) can only output 3W. You can increase voltage at the expense of current, or current at the expense of voltage; however, the total power remains the same (ignoring conversion losses).
This is false. The 3 watt rating of a dynamo comes from the German rating system which assumes a fairly low cruising speed (8mph?). A dynamo measured at the speed with a standard load (200 ohm, iirc) must put out 3W, no more, no less, and power a 6V halogen bulb. Some older sidewall dynamos had over-voltage protection, to prevent frying the bulb. Hub dynamos don't typically have that protection and can easily exceed that voltage during most of a ride. Same site OP linked to, which is a great resource for all things dynamo related, has tests of hub dynamos at different speeds and their corresponding power loads:
http://pilom.com/BicycleElectronics/HubDynamo.htm
The power of the OP's light can be measured by multiplying the saturation current (.5A) by the Vf of the LEDs at that current, which for 4 white LEDs will be in the area of 3.3*4 = 13.2V, leading to 6.6W. He could get even more by adding additional LEDs in series, which will linearly increase the total power draw, but increase the minimum speed at which saturation happens. In my experience I've found 2 white/2 red LEDs is a good compromise between peak and low speed output.
Originally Posted by
PlanoFuji
Further, your setup exhibits all of the problems common with battery powered lights without the advantage of being able to draw more power than a dyno can provide. Specifically, your optics waste much of the light generated on the sky and other areas you don't need light. You would be far better off with even the cheapest dyno lights that at least have properly designed optics to make use of the limited power available in a dyno set-up.
4 LEDs will easily have far more output than a cheapie halogen light head, optics or no optics. Versus better optimized commercial dynamo heads, most still only have one LED, so unless he is prepared to buy and chain several in series, his setup may be still more suited to his needs (the mixing of the XR-E for far lighting and XP-Gs for up close shows that he did put some thought in this.
Finally, a big advantage of dynamo lights over battery lights is that they are always on--there is no penalty for running a dynamo light during the day, making you more visible to others.
Originally Posted by
PlanoFuji
Also, rather than misunderstanding physics and arguing about it, just pick up a cheap light meter and show us the measurements.
Light meters measure lux/brightness, not lumens/output. A better measure would be to pick up a multimeter/current meter and take some measurements while riding. Take the highest sustained current, multiply it by the number of LEDs (in series), will put this discussion to rest.
Also, good job, MrBubbles. What color temperature are the XP-G R2s? Since you can get 4000K warm white XP-G2s (2nd gen) in the R4 bin nowadays, you could get a significant boost in output no matter what your color preference.