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4realestate

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For those who are considering one or the other, here it is. I was looking for something like this for a while but I always saw a tank with either one or the other. Hope this helps someone.


IMAG0048.jpg
 
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That picture only tells a small part of the story. The "K" designation that manufacturers place on lamps is really pretty artificial and no 2 brand lamps with the same "K" rating look the same. Some 14 K lamps are a lot closer "10K" than others. And some are closer to "20K". Also, the ballast that you use has a large influence on the spectral output of any of these lamps. If you go to Sanjay's lighting guide on the home page you can compare individual lamps with various ballast combinations and see accurate K ratings from independent testing.
 

4realestate

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The post was intended to give a general guideline for those of us that had not seen both lamps side by side, but I do appreciate your additional information. In keeping with your more technical addition to my post let me just add this..

Because the lamp's color characteristics tend to change during its life, color is measured after the bulb has been burned for 100 hours (seasoned) according to ANSI standards. Newer metal-halide technology, referred to as "pulse start," has improved color rendering and a more controlled Kelvin variance (?100 to 200 Kelvin).
The color temperature of a metal-halide lamp can also be affected by the electrical characteristics of the electrical system powering the bulb and manufacturing variances in the bulb itself. If a metal-halide bulb is underpowered, because of the lower operating temperature, its light output will be bluish because of the evaporation of mercury alone. This phenomenon can be seen during warm-up, when the arc tube has not yet reached full operating temperature and the halides have not fully vaporized. The inverse is true for an overpowered bulb, but this condition can be hazardous, leading possibly to arc-tube explosion because of overheating and overpressure.

As metal halide lamps age, chemical changes occur in the lamp causing shifts in the chromaticity of the lamps. Different lamp designs shift in different ways, and different lamps from the same group may shift in different amounts. Generally, over the economic life, lamps will shift 200K to 300K in color temperature. After economic life, a lamp may change as much as 500K to 600K. As a group of lamps ages together in a tank, the lamps will generally shift at the same rate causing very little color variation from lamp to lamp. However, if new replacement lamps are introduced into the group of lamps, color differences may be more noticeable, because the new lamps have not aged and shifted with the remainder of lamps. This is just one of the reasons why many users of metal halide lamps prefer to group relamp as opposed to spot relamping.

The above were clips from some of the geek websites I subscribe to which I felt contributed to the discussion, and thereby I cannot take any credit (or blame :smokin:) for the information I posted.
Spectral energy shift and spectral energy density are two other topics that involve Planck's law, which are a bit much for this discussion, that, from a scientific standpoint, more accurately describe some parts of the shifting phenomena, but for all intents and purposes probably would not
serve a good purpose going into here.




That picture only tells a small part of the story. The "K" designation that manufacturers place on lamps is really pretty artificial and no 2 brand lamps with the same "K" rating look the same. Some 14 K lamps are a lot closer "10K" than others. And some are closer to "20K". Also, the ballast that you use has a large influence on the spectral output of any of these lamps. If you go to Sanjay's lighting guide on the home page you can compare individual lamps with various ballast combinations and see accurate K ratings from independent testing.
 

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