Metal Halide question

Metal Halide is a good choice for outdoor lighting. Sodium is too yellow for most applications, it puts out more lumens per watt but the color rendition is terrible. See if you can get a model # off the fixture and look at the photometrics. You need a light fixture with a good cutoff, which unfortunately also limits the area illuminated. Another thing to consider is that MH lamps degrade significantly in light output and color rendition after about 20K hours, IIRC.

The type of light doesn't have much effect on the quality of the light. Reflectors and shades work the same regardless of the wavelength of the visible light. The main thing you want to do is light an area with all the same type of light source so that the color temperature of the light is consistent. Metal halide lights are generally the whitest most pleasing light for active area illumination.

I'm a big fan of "dark sky" myself, light pollution sucks. Generally what that means for outdoor lighting is that you either need more fixtures to illuminate your yard while maintaining acceptable shade cut-off, or you need higher mounting points for a smaller number of fixtures. There isn't anything particularly difficult about ensuring that your light only falls on your yard, basic sheet metal shades (think barn doors on a stage spot) are all you need.

The 'bounce' or indirect lighting method gives less shadow mainly by increasing the apparent size of the lamp (so that less of the penumbra is umbral, ). The better the mirrors in the light-box, and the larger the box is, the more efficient and more uniform your lighting will be. Unfortunately, there are several tradeoffs to deal with. I'll give two examples, one more practical than the other:

For bright lighting that meets dark sky rules, make a cone above your work area, with mirrored interior surfaces, with a 1200W lamp at the tip of the cone (70' above ground). At 15' intervals (down to mouth of cone, 10' above ground) install planes of mirror-surface baffles (like the Parabolic Cross Baffle or Parahex at ).

That example and the next depend on ideas like the following:

- Multiple bounces (via mirrored sides of cone and layers of mirrored baffles) spread the light fairly uniformly;

- Separation of baffles allows light from each higher baffle cell to enter several lower baffle cells, giving better mixing;

- Limited number of baffles cuts loss due to reflection inefficiency;

- Mirrored surfaces have better than 90% efficiency and waste much less light than diffusers waste, which typically is worse than 50%;

- Grazing-angle reflection efficiency often is >99%;

- High location of light directs the light at steep angle downward, limiting side-visibility of light source;

- Vertical planes of baffles reduce amount of light that angles out;

- The cone sides act like the "basic sheet metal shades" or "barn doors on a stage spot" as Pete C. suggests in his post.

In the more practical version of the above, you would make 8 small cones, say 10'x8'x8', with only two layers of baffles in each, and 150W halogen or fluorescent bulb at the top of each.

You could make a nice looking roll-around pagoda on 12" tires, coat the domed ceiling with reflective aluminum or gold, aim a 400W light up at the ceiling, and move it around to whereever you need a lighted working area. One of the 2.3m gold-covered disks as found on the Matrimandir dome might make a nice ceiling :) See (travel snap) or .

Slightly off topic, that dome has about 1500 disks with 300 to 400 leaves (surface patches) each, so over 30 pounds of gold total.

The Matrimandir has an interesting solar lighting scheme (see

near the end) which would work ok for night lighting if you move the heliostat a little higher, although that could conceivably cause problems with meeting your town's dark sky rules.

I put the light on top of the container this afternoon, and turned it on tonight. WOW. It is going to be perfect. Nice light with no big shadows, and a nice shade of a color I can't identify. Not white, not yellow, not blue. I had the durn glass off this afternoon, and cleaned the mirrors and lens, but didn't look to see what markings the bulb has. There is a transformer in a box along side the bulb housing. My buddy the electrician who got it for me said it boosts 110 up to the voltage needed.

I will post a pic on flickr, and am going to call my buddy and see if he can get any more. Good buddies like him are hard to find these days.

Steve

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Yep. Turning something on usually gives you some idea if its working or not.

Andrew VK3BFA

Please be careful that you *always* have the unit properly grounded. Ungrounded ones have killed people...

Yep. Turning something on usually gives you some idea if its working or not.

Andrew VK3BFA

Well, it does help to wait for darkness to see just how it is going to work, and to leave it unmounted so as to be able to move it around until optimum is realized. I DID turn it on during the day, but that didn't tell me diddly, except that it was working.

Steve

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It is grounded redundantly. Green lead that union electrician installed, all the way back to the house panel. He installed that panel, too. Bolted to container, and container has copper ground rod attached with solid copper heavy wire. It's grounded for sure.

Steve

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