Help Looking for replacement BLT MR11 bulb

[UFO]

Hey guys. Hope you can give me a hand

Had a bit of an accident installing my dual BLT lights. The 15w bulb is dead, and I need to find a replacement. The size is 4.6V MR11+ on the bulb, and I understand this is something specific that BLT uses. Do you guys know of any lighting supply places that would stock and sell such a bulb? I haven't had the chance to ask the LBS what Norco would sell such a bulb for, but I can imagine I should bend over and lube it up...

A 6V MR11 bulb is much easier to source, what effect would using that have on my system that was designed to run 4.6V? I have a single 4.6v 10w I can use in the mean time

[biggles604]

It is a 6V MR11 bulb. The pack is 6V 4.6Ah. You should be able to get a bulb from a lot of places, they have ~18 degree spread on the beam.
I recently swapped my BLT battery out for a 14.4V pack with 12V bulbs, there is no comparison in the brightness of the two.
If it comes down to it, I think I hae a 10W and a 15 or 20W 6V bulb lying around.

[UFO]

Thanks for the info Biggles. This is what I read which led me to ask the question: http://www.blt-lights.com/faq_bulb.htm I've got these lights: http://www.blt-lights.com/radium25.htm

The bulb I pulled out of the housing says "MR11+C 4.8V 15w". Thanks for the help

[biggles604]

Well! You learn something new every day. I didn't know they used 4.8V bulbs. Doesn't make much sense why they would do that though, the power loss for a given wattage goes up with lower voltages.
Have you contacted BLT about replacements?

[Dean W]

Overvolting (running a 4.8V bulb at 6V) produces more light than simply running a 6V bulb. If well made the light bulb will last a reasonable amount of time and produce very good light.

http://nordicgroup.us/s78/wattslumens.html

Have a look at this link. Though it does not list a 6V bulb you can see that if you over-volt a halogen bulb you produce significantly more light

[biggles604]

Yeah, but a 4.8V bulb runnin at 6V is going to get significantly hotter than a 12V bulb with a 25% overvolt since it will need about 2.5 times the current to run, and since power loss is proportional to the square of the current, it would run really warm (Given that my 12V bulb is already untouchable at +20% voltage)

[DaveM]

This is interesting. My Nite-Hawk dual is 6V. I was thinking of trying a 7.4V LI-Ion battery to see how that works, but if it's the same - a 4.8v lamp, that might be a bit much. I mean, how many voltages would they make an MR11 lamp in? I figured 6 or 12 volt. 4.8 is interesting.

[biggles604]

I don't get the 4.8V either. If you are upgrading to a 7.2V pack, it may be worth it to upgrade to a 14.4 and change your bulb.

[Hack On Wheels]

I believe part of BLT's reasoning behind that decision was that overvolting would change the colour of the light and make it closer to sunlight and therefore maybe more useable as that is the "light temperature" that our eyes are attuned to. Something like that...

[biggles604]

The light colour temperature definitely does get better with an overvolt, hotter bulb = bluer light = better penetration.

[UFO]

something interesting... i checked w/ an LBS today

the catalog lists the stock bulb for my lights as a 6v mr11 3950k (colour), the 15w sells for about $30. not TOO bad. it lists the 4.8v mr11 (no temp colour listed) as a compatible bulb, and the 15w sells for $50. ouch.