Years ago, I was doing a youth event where a guy killed the house lights at the opening of my performance - which began with a magic routine set to music. I had asked him to cut the lights when I began the chalk art segment, but he misunderstood and the whole prechalk segment was very poorly lit. Shortly after this incident I decided it was worth the extra effort to control the lighting environment during my programs.
Since the lighting in some venues may be very poor, consider investing in some stage lights or a follow-spot. I would rather have control of such technical issues than be at the mercy of well-meaning but (sometimes) untrained volunteers. So, I invested in two 850W Hedler C10stage lights and two 250W par 38 can lights, two stands, and a nifty wireless DMX dimmer system for each set.
If your programs consist of more than chalk art, this is worth consideration because, if you can’t be seen, some people will quit paying attention to what you're saying.