Default Values for Lamps with Unknown Hg Content?

John - If the lamps are no longer supplied, then you can no longer purchase them, therefore - problem solved! Remember that your mercury calculation is based on the purchasing plan, not the mercury content of your current bulbs. The presence of old lamps with unknown mercury content in the building is really not relevant - the question is, when one of those lamps burns out, what lamp will you replace it with - and what is the mercury content/lumens/life of that replacement. This credit is entirely focused on future purchases, so map out your purchasing/replacement plan to ensure a 90 picogram/lumen-hour weighted average when full replacement is complete and, as always, don't toss out perfectly good bulbs until the end of their useful lives. . .