Sigurthr
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I asked my mother in law (the property owner) when the old Hg lamps were last replaced, and I was told that they were originals from time of installation. She thinks they were put in around 1978 or so. The one on the garage lasted until about a month ago, as it was only run for about 8hrs/day during the colder months. The one on the pole was run all year around in a shady area, so it would be lit more, an it went out a few years ago.
If we assume 40lm/W and 70% loss we can guestimate the old Hg bulb to be at ~2100lm. The 55W LPS lamp is rated at >7800lm, so there is no wonder about the stark difference in brightness. In fact, at 40lm/W a 7800lm 55W LPS is still brighter than a 175W Hg lamp!
Edit: Wiki claims LPS reach 200lm/W, no wonder!
If we assume 40lm/W and 70% loss we can guestimate the old Hg bulb to be at ~2100lm. The 55W LPS lamp is rated at >7800lm, so there is no wonder about the stark difference in brightness. In fact, at 40lm/W a 7800lm 55W LPS is still brighter than a 175W Hg lamp!
Edit: Wiki claims LPS reach 200lm/W, no wonder!
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