The Utah State University Research Greenhouse complex recently replaced 160 older mogul-base HPS fixtures with 100 double-ended HPS fixtures. After four months of operation, there has been a 1% failure rate (one fixture). This is a lower failure rate than we had experienced two years ago, indicating that the quality of electronic ballasts has improved. As expected, there was a significant quantity discount from the list price.
The design goal was to maintain the average photosynthetic photon flux and achieve a 60% reduction in electric input. Measurements after installation indicate that the average PPF increased by 20%. The 10 to 20 year-old mogul-base HPS lamps had decreased in output from about 1 umol per joule to about 0.8 umol per joule, most of this decline in the old fixtures was due to 4 year-old, 1000-W lamps in the fixtures.
The manufacturer informs us that double-ended HPS fixtures are currently backordered for about five months while the supply catches up with the demand.