reflector efficiency....

All things being equal, is a two inch reflector more effiecient than a 1 inch reflector?

What do you mean with efficiency?

If used with a non-collimated source, I'd say yes. The 2-inch, being bigger, catches more of the light coming from your source and directs it where you want, which is what I would define efficiency as.

By efficiency I mean, with everything else equal, will a 2" reflector turn out more usable light at 300 feet than a 1" reflector. This is not a trick question. A laser spot light is not efficient if you want to see something at 300 feet. On the other end of the spectrum...a 360 degree flood light is not very efficient at lighting things up at 300 feet either. I suppose to clarify even further is that I'm looking for a good 20 foot bright spot at 200 feet with perhaps another 10 to 15 feet more light on each side....this is in order to light up the river in front of me at night time. I am limited by weight and power consumption, so...I was thinking that if a larger reflector is more efficient than a smaller reflector I'd go with the larger one.

More reflector surface area generally leads to more photons going towards the target and less going in all directions as spill - assuming an omnidirectional emitter like an incadescent filament or a lambertian source like a (wide-angle) LED die.

I believe the depth of the reflector needs to be considered as much as its diameter. You want to consider at what angle, off axis, the reflector starts redirecting the light for you. With the hot spot you have described and little spill beyond, it sounds like you want a pretty deep reflector. /ubbthreads/images/graemlins/icon3.gif

I use the term "surface area" deliberately.

With an omnidirectional point-source (spherical), a wide shallow reflector catches light that initially heads away from the lens.

For a lambertian flat source (hemispherical), a deep reflector catches light that would otherwise be "spill" and concentrates it.

I imagine a point source could also work with a deep reflector at the expense of spill.

Both applications will increase in "efficiency" with more surface area (extending the curve), assuming appropriate curvature.

Depth is key for throw.

Also consider the size of the source. Too much depth and the size of the source gets critical, as well as centering, and focus point.

When thinking of lambertian sources, and reflectors or lenses, also consider how much of the power is at the various angles.

If considering lenses, don't forget the ashperical style.

Different coatings will also make a difference.

Bare aluminum doesn't stay brilliant very long, and instantly starts oxidizing when exposed to air.

Well shucks. Looks like I'm gonna have to do more research. My primary concern is in seeing logs, stumps, sweepers, strainers, and rapids while doing marathon racing on rivers. Most of the paddlers are having to slow down at night time. My UK D4 sunlight dive light is probably the best light I have for this, but it's heavy, bulky, and doesn't have a remote switch or remote power option. My second best light is a Pelican headlamp with 4 lithium batteries and a 6 volt halogen bulb. It's not bad, but I think I can do better. Thanks for the replies.

I come from a radio background, but wouldn't a parabolic reflector with the light source pointed 'backwards' (i.e., towards the flashlight) at the focal point be the best way to focus a beam onto the narrowest possible spot? Then, the only factor remaining is the width of the reflector which completely governs the narrowness of the spot.

wholeflaffer,

You are onto something there that has been done by Pelican and possibly others. There is the additional consideration of thermal relief of the LED as well as mounting but to have a colimated beam with no spill, this is a good way to go.

I was going to suggest the UK Light Cannon but you have the UK D4 and it's already too heavy and bulky?

If you want to build you own mini HID system there is a Group Buy going on right now for the parts to build a 10W HID = to a 20W halogen but with less power consumption, how long do you need the light to run and what are your weight limits?

Later
Sway

PS: I recall you post from last year how did you do?

There are a couple of people who have been experimenting with the UK light Cannon, but results have been mixed. In addition there are certain minumum power requirements in order to start an HID system. D cell batteries weigh a lot. Of course lithiums are what we use in the races. The big boats only have to have light for 1 night. Solos like me have to have it for 2, 3, rarely 4 nights if everything is going wrong. That's 30 to 40 hours. We have to carry everything on portages...water, food, supplies, etc. The weight limit is simply as low as one can get it. The Texas Water Safari was postponed twice because of floods so I didn't get to run it. Now I'm focusing on the Colorado 100 next month...which is 100 miles...only one night. No portages. I may use the UK D4 sunlight in that race, and the headlmap in that race. Next year's lights are what I'm working on now. For the most part I believe I'll be better prepared than most of the paddlers. I also have so many different lights now that my wife thinks I'm crazy.