IG Pool Light Goes Off

[blue_steel]

I have a Hayward 500W Astrolite pool light in my FG pool. It's about 4 years old with maybe 300 hours of use. The light comes on and works fine for about 20 or 25 minutes, then goes off. The breaker/GFI does not trip. If I turn off the light switch and leave it be, it will turn back on the next night only to fail again in about the same amount of time.
Do you think it has to do with temperature? Once the light is on, it gets hot and the filament expands and maybe breaks free. When it cools down, the filament makes a good connection again? Just guessing since you can get a normal bulb in your home that goes out, but if you tap it, it works again.
Should I just replace the bulb?
Thanks for the help.

[Phillbo]

I'd start with the bulb, not sure what else it could be with those symptoms.