I don't agree. Distance is a great way to measure how far away to place your lights. I agree that using your hand is a very effective method of judging when it is to hot and what is acceptable. I do this always, daily, every grower should practice this no doubt. If its uncomfortable for me, its uncomfortable for the plants in most cases indoors. However, there is a general distance that is acceptable for me when it comes to indoor lighting and all natural growing styles, that distance is about two feet in general. I grow in tents and rooms, large plants and small plants, using several different sources of light that emit very different spectrum's and heat intensity. Rule of thumb for my plants to be comfortable in my experience is around two feet, sometimes further. I see steady vigorous growth with less hiccups along the way, that's my opinion based on experience, not my opinion based on my thoughts. Efficiency is the name of the game, I strive to achieve maximum efficiency and quality in all aspect of growth.