Technically, a watt is a unit of power, not light. Lumens are a better unit to use because the lumen is weighted to how the human eye responds to light. This table compares different lamps, their power consumption in watts, and their light power (luminous flux) in lumens. But even knowing the lumens is not enough information. Without a distribution diagram, in candelas, you still don't know the intensity. The reflector and lens will determine the beam angle, and hence the intensity (whether the candelas are focused exactly where they need to be). For MR11 and MR16 lamps, the manufacturer will often specify the candelas based on the different beam angles, but candelas cannot be specified for a standalone bulb (though sometimes someone will use the less useful "Mean Spherical Candlepower," which is the luminous flux divided by 4 pi). The bottom line is that lumens, and lumens per watt, are a good start in determining the optimal headlamp configuration. For more information please see: http://www.electro-optical.com/whitepapers/candela.htm and http://www.caves.org.uk/led/foot1.pdf.
|
Lamp
Type |
Normal
Voltage |
10%
Over-Voltaged |
20%
Over-Voltaged |
||||||||||||
|
Volts |
Amps |
Watts |
Lumens |
Lumens/Watt |
Volts |
Amps |
Watts |
Lumens |
Lumens/Watt |
Volts |
Amps |
Watts |
Lumens |
Lumens/Watt |
|
|
MR11 |
12 |
0.5 |
6 |
80 |
13.3 |
13.2 |
0.5 |
6.6 |
111.2 |
15.7 |
14.4 |
0.5 |
7.2 |
146.4 |
19.7 |
|
MR11 |
12 |
0.8 |
10 |
190 |
19.0 |
13.2 |
0.9 |
11.8 |
264.1 |
22.4 |
14.4 |
0.9 |
12.4 |
347.7 |
28.0 |
|
MR11 |
12 |
1.7 |
20 |
400 |
20.0 |
13.2 |
1.8 |
23.6 |
556.0 |
23.6 |
14.4 |
1.7 |
24.8 |
732.0 |
29.5 |
|
MR16 |
12 |
0.8 |
10 |
400 |
40.0 |
13.2 |
0.9 |
11.8 |
556.0 |
47.1 |
14.4 |
0.9 |
12.4 |
732.0 |
59.0 |
|
MR16 |
12 |
1.7 |
20 |
850 |
42.5 |
13.2 |
1.8 |
23.6 |
1181.5 |
50.1 |
14.4 |
1.7 |
24.8 |
1555.5 |
62.7 |
|
MR16 |
12 |
2.9 |
35 |
1250 |
35.7 |
13.2 |
3.1 |
41.3 |
1737.5 |
42.1 |
14.4 |
3.0 |
43.4 |
2287.5 |
52.7 |
|
HS31 |
|
0.4 |
2.4 |
36 |
15.0 |
Not
Applicable |
Not
Applicable |
||||||||
|
HS32 |
6 |
0.5 |
3 |
46 |
15.3 |
Not
Applicable |
Not
Applicable |
||||||||
| Luxeon V Portable | 6.8 | 0.7 | 4.8 | 120 | 25 |
Not
Applicable |
Not
Applicable |
||||||||
| Luxeon Star | 3.4 | 0.35 | 1.2 | 25 | 21 |
Not
Applicable |
Not
Applicable |
||||||||
| Light & Motion HID | 10.8 | 1.0 | 11.0 | 550 | 55 | Not Applicable | Not Applicable | ||||||||
| Light & Motion HID | 10.8 | 1.25 | 13.5 | 675 | 50 | Not Applicable | Not Applicable | ||||||||
For the 2.4 watt HS3 lamps, 10% under-voltage (which will be the case at around 9 mph), the lumens fall to approximately 26.
For the 3 watt HS3 lamps, 10% under-voltage (which will be the case at around 9 mph), the lumens fall to approximately 33.
The MR11 and MR16 lamps are most common in sealed-lead acid and NiCad or NiMH battery powered lights, while the HS3 bulbs are used in generator light sets. Both are quartz-halogen. This data shows the huge advantage of using MR16 lamps versus MR11 lamps; the larger reflector of the MR16 makes a big difference in efficiency.
By using the over-voltaging technique, you can greatly increase the efficiency of quartz-halogen lamps (at the expense of a reduction in bulb life). It is not possible to over-voltage with a generator lighting system, and in fact dynamo systems will suffer from under-voltaging when the bicycle is traveling at speeds less than about 12mph (the exact characteristics vary by dynamo, see http://www.yellowjersey.org/litespin.html for details on voltage versus velocity).
The bottom line is that battery powered lights using MR11 and MR16 lamps, are far more efficient in terms of lumens/watt than generator powered lamps. However, if you were able to find a 2.4W MR16 or MR11, it would not be as good as a 2.4W high end generator light such as a Lumotec.
4.8W LED lamps provide about twice the efficiency of a 5W quartz-halogen lamp, but at a much higher price. Lumens are only part of the equation too, as LED lamps cannot be focused into as good of a beam with the use of optics, at least not yet.
HID lamps are very efficient, but a 10% over-voltaged 10W MR16 comes close in efficiency to an HID, and a 20% over-voltaged MR16 beats an HID in efficiency. However the over-voltaged MR16 will have a much shorter lamp life than an HID.