1 it follows that by replacing old bulbs as they bum out with the new kind of bulb.你觉得混乱是因为状语从句插在了里边。如果句子调整一下语序就好理解了。 it follows that by replacing old bulbs with the new kind of bulb as they bum out。 句子的意思是：接下来就是在老灯泡烧坏时换上新的。
2 they will be produced in large enough quantities to be offered at prices comparable to those of conventional bulb.这句是被动语态，翻译时最好变成主动才符合汉语的习惯。人们要大量生产这种灯泡（句子的they），才能够使其价格能够与传统灯泡相比。