Thanks for your feedback, yes you were very close ! Actually it's not a bug, at some point the Illuminate action is capped at 50 to avoid going to high. But thanks for letting me know, I might need to add a better feedback for this.
Im mean if you lose the game and start all over the cost of light stayed, so in my second play, i started with a cost of light of like 30, so i had to restart the browser to get the cost down.