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Thread: How important is the photometric calc?

  1. #1
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    How important is the photometric calc?

    I'm an engineer,

    It seems so often that designs are so rushed that there isn't enough time to do a proper photometric analysis, we just pick the same fixture style and spacing that we did for the last job and pick the lumen package that falls in the middle of the range. How big of a deal is this? Will anybody ever hold our feet to the fire if the average fc is 35 and not 40?

    I understand some owners have fc requirements but how often does this thing actually get checked?

  2. #2
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    The avg consulting firm is not doing a photometric point to point calculation. They are lucky if they are even doing a zonal cavity calculation on a large space.

    If you use the same spacing or the recommended spacing from the data sheet, the fc levels are so close that visually, the inconsistency in the human eye from one person to another will never tell the difference.

    If you are cutting it really close for egress lighting, then you may need to do it a those very low levels. Or if you have specific numbers to prove on a zoning board application for exterior lighting for cutoff at the property line, there also you may need to prove it.
    Ron

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    Quote Originally Posted by ron View Post
    The avg consulting firm is not doing a photometric point to point calculation. They are lucky if they are even doing a zonal cavity calculation on a large space.

    If you use the same spacing or the recommended spacing from the data sheet, the fc levels are so close that visually, the inconsistency in the human eye from one person to another will never tell the difference.

    If you are cutting it really close for egress lighting, then you may need to do it a those very low levels. Or if you have specific numbers to prove on a zoning board application for exterior lighting for cutoff at the property line, there also you may need to prove it.

    Thanks for the input, its almost as if its on everyone's mind that we should be doing something but we dont have the time to do it

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    Quote Originally Posted by TheSmoothestCriminal View Post
    Thanks for the input, its almost as if its on everyone's mind that we should be doing something but we dont have the time to do it
    Also consulting design engineer in Texas:

    We'll complete photometric calcs for the following:

    1) Exterior lighting (parking lot / walkway / entryway)
    2) Interior lighting (only if we need to meet specific target values, or if we are trying to evaluate a space that is unique, egress lighting calcs)
    3) Sign / facade lighting to meet a specific level
    4) Parking Garage Lighting
    5) Roadway lighting, only if a municipality does not have specific requirements already or set spacing
    6) Tunnel Lighting
    7) Specific task lighting (IE/ Repair Garage, Manufacturing facility), where IES has defined certain lighting levels for those special tasks
    8) As required for Hospitality/Healthcare/ Texas Health Code (50fc requirement for kitchens in Texas)

    A lot of factors run into photometric calcs and with the changing LED technology, and their optics, we've found the old spacing with fluorescent lighting to be dated, or sometimes not applicable in specifying equivalent lumen packages.

    I think if you have a typical office layout, we have done enough of those that typical spacing and what you've mentioned may work no problem, but it's good to get into the practice of it every now and then when you need to defend your design.

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    I still use Visual 2.06 and run photometrics on almost every commercial job that goes through my office. The only exceptions are when the client provides the lighting design. Most consultants I've talked to send the job out to a lighting rep and have then do the studies. I prefer doing them myself. I've worked with some reps who do an outstanding job, but at some lighting rep firms the photometrics are run by people with, shall we say, limited training.

    Would a client notice the difference between "rule of thumb" spacing and custom layout? Probably not. I'd know, and it matters.

    2X4 was the best price point for fluorescent. 2X2 is usually the best price point for LED. The optimal spacing is different.

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