There are quite a few differences between the Arc AAA and the Photon II. In one catagory is construction. The Arc is build very well and is completely waterproof. If you look at the Photon II, there is no attempt to waterproof it at all.

The Arc is almost impossible to accidently activate thus, so you are not likely to find it dead when you need it. The Photon requires a jewler's screwdriver to change batteries (no changing in the dark for this one) where the Arc just unscrews and drops in.

On the next front are the batteries. The Photon II white uses 2 x CR2016 batteries at 75 mAh each and the Arc uses a single AAA battery. When you add the two CR2016s together and account for the voltage difference between it and the AAA, it probably looks something like this:

Photon II = ~300mAh (1.5v equiv)
Arc AAA = 1250mAh

Obviously there is a lot more battery capacity in the Arc. I wasn't able to find a Photon II runtime graph, but I was able to find a Photon III chart which should be pretty much the same (probably compare to the "high" setting).

I think this illustrates the story:

http://ledmuseum.home.att.net/pho3.htm



this_is_nascar's Arc AAA runtime



Also note the last graph shows the Arc AAA with normal alkaline batteries AND the new AAA lithium batteries. Here is a discussion of new AAA lithium batteries

You'll note the Photon drops off very rapidly from the start and then runs at signficantly reduced output for quite a while. The Arc on the other hand runs pretty much full brightness for about 5 hours. More with the new lithium battery. Oh, and while the charts don't show it, the Arc also keeps running at a low output rate for a long time as well.

On the other hand, the Photon is VERY small and VERY light, It is less expensive, and it works just fine.

-john