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Like Hawk said, place your hand at the top of your plants, keep it there for at least 30 seconds, if it doesn't get uncomfortable, it will be ok for your plants.
Also, some strains can be sensitive and even though there may not be too much heat, the intensity can shock your plants. Probably not going to be an issue with your 150w, but just something to keep in mind if they get droopy and light is still passing the hand test.