It sounds like you ought stay with your HID system - 1100 Lumens @ 18W is around 64 Lm/W - substantially better than any production white LED can do.
I have an extensive
database of white LED specs and rudimentary calculations if you want to do some research.
Better high-power LEDs average 20-25 lumens per watt. Low-power 3/5/8/10mm thru-hole LEDs can do a bit better, but at the expense of "lumen density."
Your "superbright" 5mm LED is probably rated to 20mA x 3.5V, which comes up to 70mW. I'm calculating 9k mcd x 30 degrees at around 1.93 lumens, for a decent efficiency of 27.1 lumens/watt. Pack around
600 of those together and you can get >1150 lumens. Of course you'll need to supply 42 watts to the array, and 5mm LEDs can't manage heat
at all.
The Luxeon V portable is the most powerful single LED on the market today. They commonly put out around 20 Lm/W, but can theoretically go as high as 40 Lm/W (the famed and rare X-bin). Bear in mind that the design lifespan for this emitter is 500 hours. Assuming you get lucky with W-bin emitters, putting out 148 Lm @ 5W, you'll need 8 for 40 watts. Expect to pay around $40 per Luxeon 5W emitter.
$320
You could do better cost-wise and be looking at around 20,000 hours of design life with the Luxeon III 3W emitter, which can be driven at close to 4W. A somewhat-premium T-bin emitter can do 84 Lumens, for 21.54 Lm/W. You'll need around 14 emitters & 55 watts of power. Expect to pick up LuxeonIIIs for around $15 each.
$225
You could experiment with the Lamina Ceramics
BL-3000 integrated array - a pair of those might get you close to 1300 lumens... but their efficiency isn't as good as the Luxeon - 23 Lm/W, so plan on 49 watts to a pair and make sure you heatsink the bejeebers out of them. Expect to pay somewhat over $150 per BL-3000 array,
if you can find them.
>$300
I don't see any engineering economy for LEDs in this application. I'm sure that HID bulbs & ballasts are costly, so perhaps it coulld be justified on a long-term cost of ownership basis.
If you can't meet the above criteria, you could just do it for the heck of it /ubbthreads/images/graemlins/evilgrin07.gif