What is the difference between 'hard' and 'soft' Jhanas? I have on a few occasions come across the distinction between a 'hard' and 'soft' Jhana and would like to know what the experiential distinction between these two terms might be.
Here is a quote on the terms "Hard and Soft Jhana" from the book "Mastering The Core Teachings Of The Buddha" by Daniel M. Ingram, p. 136-137:


  "Many traditions use the breath as the primary object initially and then shift to the qualities of the states themselves as the object of meditation when they arise and the concentration is strong. The quality of a jhana can either be “soft” or “hard” depending on how solidly one is in the state. In soft jhana, the qualities of that particular state are definitely recognizable in a way that is different from the ordinary experience of those qualities to the degree that we are confident we are in the altered state defined by those qualities.
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  Concentration vs. Insight
  
  In really hard jhana, it feels as if our mind has been fused to those
  qualities and the object with super glue, as if we were nothing but a solid block or field of those qualities or that object, as if they and the object were the whole world with nothing else remaining. Getting into really “hard” jhana states dramatically increases the beneficial effects of the practice, though it takes greater strength of concentration and usually requires more favorable practice conditions to do so. Taking the beneficial factors of the jhana solely as the object of concentration is helpful for this, as can be using an easily identified external object such as a candle flame or colored disk."