I know, I should buy a meter but
Meanwhile I want to get a rough idea of what light intensity I have in an area. I tried the shadow on white paper. That works somewhat.

However, I placed a table lamp next to the plants. I turned on a 60 watt incandescent and it doen't increase the light/brightness in that area.

I put a 100 watt incandescent light in the same lamp and it does increase light/brightness.

For African violets, can I translate that test into some meaningful measure? Enough? Not enough?

I can use the plants as light meters. If they sunburn, too much light. If they get leggy, too little but that seems a very inefficient and slow way to go about it.