There are two fixtures at the building I maintain that currently are using CDM100/PAR38/FL/3K metal halide lamps.  When I took over the building it was in pretty tough shape with many, many broken fixtures.  I failed to look properly at the electrical drawings and replaced two bad ballasts, one 70 and one 100 watt with two new 100 watt MH ballasts thinking that was proper as we had like a dozen 100 watt MH lamps on the shelf.  Turns out the lighting for this area was designed to use 70 watt MH lamps, not 100 watt.  A dozen lamps and a dozen burnt through pieces of diffusion paper later, it's time to replace with LED lamps as the 100 watters were not correct anyway.

The lumen rating for a 70 watt MH lamp is 4800.  No LED I have seen really comes close to this, although I have seen lumen ratings for some LED lights as high as 3000.  I thought that lumens are lumens but LED lighting has always seemed brighter than the "equivalent" incandescent.  Is this also true for MH lighting?  I want to make sure that there is adequate lighting for this area but I also don't want to make it too bright as it is now.

Is there sort of a metal halide to LED equivalent chart?  I need to spend wisely around here and can't buy half a dozen lamps to "audition" them to see what looks best.

Thanks-

Val

All HID lamps (Mercury, LPS, HPS and metal halide) are brighter than their equivalent LED retrofits.

The required lumen rating depends on the optical efficiency of the original light fixtures.
The major difference here is, the HID's are rated as the bulb alone, but part of that light get lost in the fixture when redirected to where it is actually needed.
But with LED lanterns, the rated lumen output is measured already with all the optics (as it is integrated with the LED modules).
This rating inconsistency creates a lot of mess and errors, when converting from one to the other, as the optical efficiency of fixtures is often nowhere to be directly specified (it is "hidden" within in the beam pattern diagrams), so it is hard to match the rating. It depends on how the beam pattern looks like, how the original lanterns performed,...

Plus on top of that is the way different aging profile (the way how each light source degrades over time) and the way how the lumen output is specified.

So I'm afraid you won't be able to match the light output exactly, so you would have to start from scratch: Get the required lightning level specifications, then go through the documentation of fixtures available for you to choose, calculate the illumination levels and try to match it with the requirement.
Important note: When deviating from the specified level, remember the variation in the illumination is way more visible then the absolute light level. That also includes the light contrast with surrounding areas.

Fortunately the eye tends to register the light level as a log(light level), which means even when there is half lux levels, no one would notice unless having some form of absolute reference. So if you keep the pattern the same as it was (fixtures at the same places, with the same beam pattern) and the light output will be at least order of magnitude the same as it was (3000lm LED is very similar to 5600lm HID; when assuming some losses in the HID optics and the lumen depression of the HID, it will be very similar or at least not that far off), you are fine.

Remember, +/-30% in absolute intensity is on te border to be noticeable at all, but differences of 10% between two neighboring sections is pretty well visible.
As the original (as far as I understood your description) was a bunch of the same model fixtures, the consistency won't be that difficult, when using again everywhere the same assemblies.

@dor:
Yes, it would be probably better if HID fixtures would be available, but tat is not the case, so the only option is to use what is possible to get. And what will be supported even through the life of the installation. It does not make sense to install expensive HID fixtures now, when within 3 years the replacement lamps would be bare unobtanium.

Medved-

Thank you so much!  Based on your notation about the lumen levels of LED's as compared to HID's, I will probably select these as replacements:

https://www.1000bulbs.com/product/211134/GREENCREATIVE-98211.html

2500 LED lumens should do the job of a 4800 lumen HID.

Val

I thought you are about to use some decent purpose made LED lanterns, namely with good sized heat sinks (similar to those used in road lanterns).
Here the PAR lamps are very rarely used, so I tend to forget they even exist (even though you have mentioned it)...
The thing is, first the PAR lamp has all its optics already as part of the lamp, so the lamp lumen rating should already include its losses. So there the same lumens should practically mean the same illumination, assume you use the same beam angle rating (that is important, as 60deg needs double lumens for the same illumination level as the 45deg one, because the 60deg illuminates twice as much of an area).
But the fact the eye is rather insensitive for the absolute light level still means you can easily get away with that, if the beam angle is similar (so the illuminated area isn't smaller).
The main problem I have with these integrated products is the limited heat sink surface area. That tends to shorten the life time (but that should be included in the official life rating).
On the other hand the advantage is, you don't have to worry about availability of any replacement parts: When due to relamp, you will just order what would be on the market at the time of relamping.
And I would recommend do that relamping of all lamps in the installation at a moment you may write off all of the bulbs as at the end of their useful life (even when many will be still working - use them elsewhere, where they do not have to match to anything other; unless the lamps start to drop out already when nearly new): That way you will ensure the lights will remain consistent with each other, mainly related to the exact light color tone. First it may not be the same anymore, plus the color tends to shift over time sightly, so fresh lamp may be different from the worn out ones...