I have a small office building with High Pressure Sodium wallpacks approx 8ft up the wall for security. It is in a neighborhood setting. They are about 10 years old, have had 70w bulbs in the 100 watt fixture, constant cycling, even on new 100w bulbs, polycarbonate lens are yellowed and I'm thinking its time replace them.
I'm considering Metal Halide rather than HPS, and thinking 70 watt rather than 100 watt. Seems the lumens will be sufficient and less bright may make the neighbors happy, but the whiter light should help for security, especially if video cameras are installed.
Also, these are on photocells. Some have their own in the fixture, and other packs are wired 2 or 3 to a cell in the eves. Kinda screwy but it seems to work except that they stay on late into the morning when not needed.
So I'm wondering if I'm on the right track for the HPS vs. MH.
what is the difference is efficiency? What else should I consider. I've thought about LED but not ready to go there yet.
Also, any suggestions for a timer to replace photocells? I don't think these are all on the same circuit so does that mean I will need several timers?
With these types of fixtures, you HAVE to use the lamp that the ballast is made for. The ballast will tell you a type of lamp to use, it might even tell you on the reflector. You cannot change type of lamp or wattage of lamp or it will do just as you describe. The cycling you are describing could be caused by a bad ballast which may have been caused by using the incorrect lamp. The cycling could also be because the lamp went bad because it was being powered by the wrong ballast.