Lighting illumination levels

[skeshesh]

Good day everybody - hope all is well.

For a project that's aiming for a certain LEED goal I've encountered some issues with the clients design standards. They call for 40-60 fc in an office space; our design concept is to have a level around 30fc while making sure to have generous lighting levels using task lighting incorporated in the office furniture. Has anyone encountered situations like this? Am I in the wrong to think this is an acceptable approach and level of lighting? I believe the IESNA standards would classify this area as category D but I don’t have any other references to justify my approach. To reach 40-60 fc we would need to increase the wattage or number of fixtures. That would force compromising several LEED points which I'm trying to avoid. All input is much appreciated.

 

[cyriousn]

I would say you are okay with the 30 fc level with the task lighting. If you get a chance buy a light meter and actually show people the difference between 30 and 50 and most people woudnt even notice a difference. Are you going after the daylighting and views points or doing any daylighting? Daylight will give you a fc boost. Its certainly hard to hit those 50 fc numbers while keeping the power density down. I've heard from some of the lighting reps I work with that they are revising the IESNA standards to lower some of the fc levels to go along with all of this LEED business. Usually we are using geothermal hvac on our projects so we dont have to be as picky on the lighting density to get our points.

 

[skeshesh]

Thanks for the response. I agree that 30 is acceptable considering provisions for furniture installed task lighting. The problem with this project is there are some design standards tied to the funding of the project that call for 40-60f.c. while also targeting a Silver certification. I do lighting projects regularly and have also contacted several excellent application engineers that I've worked with in the past who have decades of experience working for lighting distributors; the result is that this is just an unrealistic expectation considering the criteria and what's available on the market.
We also have 2 points (perhaps 3) attached to LTG wattage reduction, another 2 for daylighting controls (1 for %50 fixtures on daylighting and 1 for perimeter offices) under Energy and Atmosphere (EAc1.1) & (EAc1.2). The daylighting controls will also contribute 1 point to daylight and views under Indoor Environmental Quality (EQc8). So we potentially have 7 points attached to lighting. But even with the contribution of daylight the goal simply seems out of reach.

 

[cyriousn]

Are the efficenices of the general ligthing fixtures at least 90 percent? Are you specifying lamps with the highest eficacy possible? Make sure you are taking the wattage of the lamp/ballast combo and not just the wattage of the lamps, last dimming project i did the ballast factor was around 0.88 shaving off a few watts consumed. Not to say you havent done this already but these are a few things that I try to double check when comparing the design to the power density. It certainly makes it a pain when you are adjusting all of these things and redoing the lighting calcs. Sounds like your in a little bit of a jam as they have tied some unrealistic requirements to the funding. Silver shoudnt be too difficult to obtain as long as the owners didnt heavily lean on the MEP guys to obtain all of the points when they started filling out their desired point checklist. Just a questions but are you guys using energy modeling software for the EA credits and if so what software package. The guys at our firm seem to use Equest and Trane Trace.