First, what MartyE said!
Second, ZWs have a plaque either on the top or the back of the transformer. The wattage is listed there. Most are 275watts. Figure 80% of that for a realistic value.
Also, old ZWs are noted for having the circuit breakers fail and trip early. (The red light indicates the CB has tripped. Once it cools down, it automatically resets and the red light goes out.) A good train shop can upgrade your ZW with a solid state CB. They are not terribly expensive , and well worth the $$, in my opinion.
If you find the wattage of all your bulbs exceeds 80% of the ZW's rating, you need to a) remove some bulbs, b) convert some bulbs to LEDs with lower current draw, or c) add another transformer. If you go with c), be aware you need to split your lighting circuit into at least 2 circuits, one for each transformer. Also, if you have a common ground between the transformers (this normally the case) you MUST be certain the transformers are properly phased! There are lots of videos available explaining how to do this.
Chris
LVHR
