Patrick...good points...although the use I've tended to see people make of helmet mounted lights for the street has been as a secondary or auxiliary role to handlebar and seatpost or rear rack mounted tail lights. At least that's what I'm thinking the use of a double ended light would be. I've read that some people use helmet mounted lights to view the road or trail, but the strongest argument I've heard for them mounted atop helmets is for the 'be seen' purpose.

For a variety of reasons, aesthetics, aerodynamics, functionality(easy for it to snag onto stuff when mounted there.) I don't particularly like the idea of lights mounted on top of bike helmets. A possibly better idea for a helmet w/headlight-tail light would have the helmets' shell somehow shaped and contoured to provide a port for the light. But of course, since the primary purpose of a bike helmet is to provide shock absorption to the wearer's head in the event of a crash, the helmet mounted light being able to 'break-a-way' in the event of an impact to it would probably be essential so that the body of the light doesn't come between the helmet wearer's head and the surface being impacted, negating the shock absorption capability of the helmet.

There's been some discussion in this bikeforums category about the fairly recent kickstarter proposal for a bike helmet with integrated front light. People commenting here were wary of possibly poor ventilation...too low lumen lights. Manufacturers of fireman's helmets and motorcycle helmets have made some efforts to come up with lights on their helmets, but what I saw in web searches didn't seem to very desirable for use on a helmet used for biking.

Perhaps, perhaps not! The light on your helmet doesn't need to be as bright since that light will mainly focused on an area close to the front wheel, and the occasional flash through a drivers side window or a street sign. The bar light is intended to shine further distance thus should be the brightest of the two lights. I use a Cygolite MityCross 480 (480 lumens on high) on the medium setting for my helmet light and at that setting it puts out more then enough light for my needs at about 320 lumens. So it depends on how crazy you want to get, personally I would just get a ExpiliOn 400.

In case your wondering I use the Philips Saferide light on the bars, this light is fantastic, it may "only" put out 400 lumens but due to the aiming (low and flat like a car) of the beam is equal to 1000 lumen light. Run time on high is bit short at 2 hours but on low it will run for 8 hours. I usually run it only on low but occasionally on dark country roads with no moon, or raining I will crank it to high, but I rarely ride for more then 2 hours after dark anyways. Besides after the 2 hours on high it shuts down to low and will run for another hour. Batteries are readily available for it too since they use 4 AA rechargeable bats and not some dedicated pack. You would have to pay at least twice as much for a different light to get the same or more output then the Phillips. I consider the Phillips to be the sweet spot in lights, just the right amount of light without being an overkill at just the right price without taking you for everything you have, very much like the Cygolite ExpiliOn 700. The difference between those two lights is the ExpiliOn uses a flashlight type of beam, and the Phillips a car like beam which projects further without hitting drivers eyes.

If you want to wait for Christmas, save up a tad more and get the Phillips and then use your current ExpiliOn for the helmet.

The point of getting another Exp 700/600 is to have a second bar mount and battery. I could use the 2nd light on the helmet mount that came with this light I just got, and then put the 2nd light's bar mount on my other bike.

That as opposed to buying just a second mount and second battery, for more than half the cost of a Exp 600.

In my experience, when helmet mounting lights like the Exp, it's best to put them squarely on top of the helmet due to their length and weight. This keeps the helmet better balanced and positioned on your head and can be less tiring, particularly when mtbing in rough terrain.

well yeah but I think it would also be somewhat dictated by the location of the vents on the helmet. In the case of my helmet the mount would have to just slightly forward of centered on the very top of the helmet.

Another factor to consider is the riding position of the rider. Both my wife & I wear the same type helmet with a Trustfire AA flashlight secured by a Zefal Doodad. My riding position is more aggressive, leaning forward...my helmet light is mounted centered and slightly to the rear. Her riding position is more upright...her helmet light is mounted centered and slightly to the front. We run our helmet lights mostly on strobe mode. YMMV.

Top only coincides with the center when the helmet is level. In both your and your wife's cases, it sounds like you both mount the lights "squarely on top" of the helmets. Since yours is tipped forward compared to hers, the tops falls at a different positions with respect to the brim of helmets. If you mounted them centered on the helmet, it would be in front of the top in your case and behind the top in her case.

Roger that. That's what I was trying to say. GMTA. Safety first.