I was under the impression that you lost some, very little, but some lumens. Just as you stated, I wanted to get the even spread throughout the garden without a reflector, and the added bounus of the specturm difference almost had me, however....the lumen loss made me go with the typical MH (clear blulb). Now I'm pissed
...time to medicate!
That is correct, there is nominal lumen loss of approximately 1000 lumens or 4.3% (23,500 versus 22,500)
IF you are burning these types of lamps in a vertical orientation (base up).
However, if you are burning these lamps in a horizontal orientation then there is no difference (20,500 versus 20,500).
Yes, you read that correctly, HID lamps are sensitive to vertical or horizontal orientation and a horizontal burn position will cost you more lumens than coated versus clear.
This has to do with the mercury in the lamp as it prefers to condense in the point furthest from the arc tube (the hottest part of the lamp) and can do so more readily in base up position.
In a horizontal burn position the mercury tries to condense too close to the arc tube and can't, resulting in less than optimal lumen output.
The same concept applies to compact fluorescents.
Just for a change of pace though linear fluorescents prefer to be operated in a horizontal position.