Hello,

I'm new here, and have some questions about light fixtures.

1. What is the difference between "NEMA" fixtures and "Yardblaster"-type fixtures?
2. Where can I learn more about the history of NEMA fixtures?
3. How bright is 175 watt Mercury Vapor compared to 100 watts of Metal Halide?
4. How does the brightness of 70 watt Metal Halide compare to 100 watts?
5. About how much do these Dusk-to-Dawn fixtures cost to run each month (in terms of 175w MV, 70 & 100w MH and HPS)?
6. A lot of NEMA/Yardblaster lights are available in 10" and 12" refractors - Are there any advantages/disadvantages between the two sizes?
7. How do the newer 65 watt CFL Yardblaster types compare to the MV and MH models?

I look forward to learning new information here at this forum!

Thanks,
-Gil

3. Some numbers from GE-lighting web:
  175W MV: ~6700lm mean (7800lm initial)
  100W QMH (pulse-start): 4900lm (7900lm)
  100W CMH: 6300lm (8700lm)
  Strange, then GE web put the same lumen rating for both clear and /DX 175W MV lamps, i would expect clear being lower. However the clear lamp might regain the difference in better efficiency of some asymmetrical refractors (those designed to send less light to the wall the fixture is mounted and redirect it forward/sideways - the large surface of coated lamp eliminate this effect, so more light is wasted on the house wall).
4. ~60%, new 70WMH is comparable in output with worn out 100W MH
5. Count ~10hours/day, +15% extra (compare to lamp rating; for HPS it would be slightly less, as the simple series choke ballast is more efficient then transformer types) power input for ballast losses (so MV175W fixture consume about 200W)
6. Larger refractor = bigger, so more difficult to handle the fixture, but less glare
7. Light output close to 70W QMH at the end of it's life, rather short lifetime, poor optical efficiency (large surface area not matching the refractor), very bad reliability (high chance it damage the fixture at it's EOL by the smoke - nearly impossible to clean it out from the plastic refractor)

As I've seen it used, "yardblaster" is just a term used to describe an outdoor light fixture which illuminates a wide area.  A NEMA head refers to a fixture which complies with specific standards set by NEMA (National Electrical Manufacturers Association).  Fixtures which follow NEMA standards have interchangeable reflectors and diffusers.  Another member on this site may know more about exactly what those standards entail.  Some fixtures sold as "yardblasters" are also NEMA heads but many that look NEMAish do not follow with the standards.  That doesn't mean they're necessarily bad fixtures, just don't expect that you'll be able to find replacement parts from anyone besides the manufacturer.  Certain components, such as the ballast and photocell may be standard even on bucket lights that are not true NEMA heads.  Also note that NEMA heads can use diffusers besides the typical bucket, such as gumball globes or full cutoff refractors (which make the light less of a "blaster").  Here is a site with some history.  You might need to use Internet Explorer to see the pictures.  The URLs to the images are malformed and don't work in Mozilla. 

Mercury vapor is going to be the most reliable, but it is also the least efficient.  You might have difficulty finding a fixture now that their manufacture has been banned by the latest U.S. lighting efficiency standards.  Both fluorescent and metal halide fixtures can be reliable, but a low quality electronic fluorescent ballast may be more apt to fail early than even a low quality magnetic HID ballast.  Pulse start MH and HPS have igniters which adds another possible point of failure not found in MV fixtures.  Another member on this site know more about how replaceable these components are in a typical yardblaster and whether it's usually better from a cost standpoint to simply replace the fixture when something goes wrong.  A true NEMA head or other commercial quality outdoor fixture will have replaceable internal components, but of course the initial cost will be higher. 

The 65 W fluorescents appear to be listed at anywhere between 3800-4550lm.  I'd be hesitant about the fluorex style fluorescents because they seem to be a de facto standard, rather than anything official.  Someone else here might know if this is the case.  I have yet to see any made by the big 3 (GE, Philips, or Sylvania).  With HID, if you are disappointed with the quality of a particular bulb, you can always buy one from another manufacturer.

Thank you both for the info!

Here's another one: With Metal Halide yardblaster types, are there any advantages/disadvantages of having a closed-bottom lense versus an open lens? I've seen both.

It sounds like you are searching for the best fixture to use as a dusk-to-dawn yard light.

For the best in reliability & durability, get a true NEMA (with latch-on refractor) 175w mercury fixture. They can still be found at garage sales & craigslist sometimes, but are getting harder to come by. A 175w mercury fixture will use as much electricity as running two 100w incandescent lamps. It's probably efficient enough for home use unless you have more than two running dusk-to-dawn.

For the best of current production, probably get an all-metal NEMA-style fixture, though some of them unfortunately have refractors that yellow quickly. 70w should be fine for small-to-medium yards, 100w for a large area or if you need more light for outdoor activities/sports. I use HPS for my general security lighting as it last longer, costs less & the amber light disturbs my night vision less, but metal halide is much better for doing any task under & makes plants look better (and is best for lighting a swimming pool or ball court).

Unless you enjoy repairing electronics, stay away from the Fluorex lights. The one benefit is instant-on, but they often actually start up quite dim just like a metal halide lamp. The housings are usually thin plastic and the ballasts just don't last. I've seen many failures.

Open bottom vs. closed? Closed-bottom will collect bugs, unless it's amazingly well-sealed. If you use metal-halide lamps, always use the protected (shrouded)-type lamps if you have an open-bottom fixture to help protect against lamp explosion. In fact, it's better to spend a little more for shrouded metal halide lamps anyway, even in a closed fixture....it's a pain to clean up the mess of an exploded lamp (not that they always explode, but they are more likely to than other types of HID lamp).