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John, the mr16 and mr11 bulbs both work great. I don't like the lazer beam that some people use on their test tube lights, but the tightest beam you can get on an mr bulb is perfect because there is enough light around the edge of the spot to even out the contrast between too bright and the darkness. 12 degrees is the tighest, not all that tight. By last longer I assume you mean rated life, not burn time- which is the same for all bulbs of the same wattage. Most mr16 display (not projector) lamps are rated at 3000 hours. The mr11 are rated at 2000 hours except the 50 watt which are 3000. It has been many years since I had a bulb burn out. Usually after several years it will eventually get dropped, which usually breaks the filament. Rated life of display bulbs (such as you get from hardware, electrical or home depot stores) is not a factor. Also, you need not worry to much about overvoltage. First you are likely to be losing as much as a volt to your wires, switches, connectors, etc. before the power reaches the bulb. Second, bulbs lose a fairly low percentage of their rated life to overvoltage as long as it is not much over 10 percent. (sorry, forget exact numbers). This small loss is easily withstood by a 3000 hour rated bulb. For many years I used a 14.4 volt nicd (remember nicad is a registered trademark of SAFT) battery with no burn out problems. Also the initial voltage of lead-acid cells drops rather quickly to near 12 volts, or even less, as they deliver less voltage under heavy loads. There is a very handy bulb chart in the MAY/JUNE 1995 issue of Underwater Speleology, including other useful info. Contact Bruce Ryan 71573.1073@co*.co* for a copy. I have a biologist friend who must spot tiny critters- he will use nothing but an ESX 20 watt or FMT 35 watt mr16, or the equivalent mr11. I feel the same way. Also we agree that the 35 watt lamps have an equal or better beam to the 50 watt, with much better burn time. You may also find bulbs listed by commercial numbers such as 35MR16/Q NSP/P 12V , 35 being the watts, NSP being narrow spot (my favorite bulb). Dive-Rite (905) 752-1087 sells all the bulbs most useful for diving. I made a nice light using a homemade battery pack and one of their MR type heads- they have both mr16 and mr11, I prefer the mr11 for its small size. These days people are selling MINI 12 lights so close to 300 dollars that I don't bother to make my own lights anymore. That should about cover it. Safe diving, Paul Smith
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