According to the BTZS book, Delta 100 in D76 or ID11 1+1 with Ilford's recommended times is pretty much smack on the nose of ISO 100. You can therefore use that as a reference for the amount of light coming from your enlarger if you run some tests on Delta 100 at the same time (films exposed concurrently, preferably) as your other films.

Or, apparently (I have not verified this) if you get EV1 on a light meter, that implies a 1s direct exposure onto ISO 100 film to hit Zone V. Adjust accordingly depending on your film sensitivity and how far up the step-wedge you want to go.

You want to keep exposure to no more than 0.5s in order to prevent reciprocity failure from destroying your results, unless of course you're trying to make reciprocity-failure measurements. The other issue is that with many enlargers, the bulb takes a good fraction of a second to warm up / cool down, which means that a large part of a short exposure will be at a lower intensity, which means you're going to have reciprocity failure anyway; you can cure that if you put a good mechanical large-format shutter on your enlarger and use that to control the testing exposures (make them square-waves instead of trapezoidal).

Have you considered bouncing a known-power flash off the ceiling of your darkroom from a fixed location and using a flash-meter to get the power level at the tested film? Again, you can calibrate the exposure from your flash/room combination using Delta 100 as a reference-point. And a flash will be much whiter than an enlarger bulb, which is good when you're testing films (like Acros and CHS-25) that don't have a lot of red sensitivity and for which you would under-estimate speed using a tungsten light-source.