I have a Hayward wet niche fixture that for the last few years, turns itself off after being lit of about 10 min. It cools and turns back on for another 10 min or so and repeats . I looked at the fixture before replacing the bulb a few years ago and was unable to determine what wattage that the replacement bulb should be because the ink used to mark the bulb size had long since worn off. I assumed it was a 500watt bulb only because there is only one light and the pool is 20x40. I ordered a 400watt bulb to replace the one I have in it presently. Given the described problems with the 500watt bulb, does it sound to you that the problem was due to too hot a bulb? I wrote to Hayward and asked the same question. I'm awaiting their response and will post it here when I hear from them. Thanks all.