Originally Posted by slvoid
A standard halogen should get around 20 lumens/watt.
L&M's HID gets about 675 lumens at 13.5 watts.
That means that your 30 watt halogen light's making 600 lumens. If you can only safely travel at 13mph on 600 lumens, 675 isn't going to get you any more.
Anyway, to find the distance to reaction time and speed, distance=mph*1.46*reaction time.
So for a 2.5 sec reaction time, you need to be able to shine a light about 65ft.
Much improved spreadsheet. I don't understand the differences between:
1. avg city speed
2. max speed
3. road max speed
Why would road be higher than city with the same light?
I had my objects reversed and overstated the range, here is the corrected numbers
light______dark___light
10 watts____40______70
20 watts____58______95
30 watts____58_____115
Formula for feet/sec at 2.5 sec reaction time:
1. convert to feet/second: /2.5
2. convert to feet/hour: *60*60
3.convert to mph: /5280
thus
@round(((Distance/2.5)*60*60)/5280,1)
Results for safe speed
Light______dark ojects____light objects
10 watts_________10.9_____________19.1
20 watts_________15.7_____________25.9
30 watts_________15.7_____________31.4
Slvoid's formula for same light
Light___________city______________road
10 watts_________15________________20
20 watts_________20________________27
30 watts_________23________________31
Conclusion: Slvoid's value are accurate for light objects. However for dark objects, like rain covered or for dual light systems where one light may be a flood and the other a spot, the speeds are too high.
For new riders, remember the max road speed is for dry conditions and to avoid overriding lights you'll have to adjust for: fog--rain--mist--wet surfaces--snow--leaf obstruction.