Buy a transmission step wedge test. They're about 20 bucks and give you immediate feedback on every burn as to how much light has come through. Emulsions have so much latitude in terms of acceptable exposure that for the kinds of printing I assume you're doing, a step-wedge test will do the job of an integrator. As your bulb ages and you find your test is washing out lower and lower, adjust your exposure accordingly. You can get them from Stouffer.