I'm no expert on Jonna's technique, Susie, and I am sure she will answer you much more satisfactorily later, but she may still be on holiday.
@JonnaSudenius will correct me if I am confusing her with someone else that uses her method exclusively, but I don't think she uses either heat or light to start, just sowing the seeds in the closed vermiculite system and putting the containers under her bed until germination.
