Haven't seen much evidence that "nit" light levels (luminance across surface) are readily documented, particularly since signs are often customized fabrications. Has anyone identified a reasonable method for project teams to calculate performance if internal light fixture is known.....not sure if one can extrapolate nit light levels using initial lumens? I'd expect the color and opacity of the sign surface to be a major factor as well.....light emitted from a thin gauge white plastic sign face would be brighter than a thick gauge dark blue plastic, for example.

Welcome any tips to overcoming this obstacle, particularly when eliminating internally lit signage is not an option and all other credit requirements can be met by the Project design!

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Bill Swanson

Sr. Electrical Engineer

Integrated Design Solutions

LEEDuser Expert

516 thumbs up

Mon, 09/24/2018 - 20:54

This is a documentation problem. When I complained about it the response I got was, "Candela per square (cd/m2) and nits are two names for the same the same thing. The universally accepted metric for luminance. In my opinion, luminance is really the only useful metric for this. The luminance metric is apparently used by the sign industry. See the USSC Sign Code http://landuselaw.wustl.edu/ordinances/usscmodelon-premisesigncode.pdf see page 48. (their limit of 750 is way too high of course). The sign fabricator/supplier should be responsible for certifying that the sign will meet the luminance limits and all the LEED applicant should have to do is submit that certification" The only place I ever find information about 'nit' light levels is from TV manufacturers. This would apply to the video billboard type of signs that can get new images programmed easily.

The more traditional sign companies don't have this. When this credit came out I called up 10 sign companies to see if I could get information from them. 5 local companies and 5 from a large city. Most had no idea what I was asking for. "What the hell is a nit?"

I don't know of a good way to convert lumens (luminous flux) into nits (luminance). If it's not a video screen designed for daytime and nighttime use, I don't think the traditional signs are a problem. I just can't document they aren't a problem.

I was told there is a phone app I can download to measure nits with my phone. I tried one a few years ago and it didn't work well in my opinion.

Ask the sign manufacturer for the information. When they can't provide it, contact USGBC and ask them how you should document it. The conversation previously was started from questions to USGBC about documentation.

Joanna Switzer

Sustainability Project Manager

Atkins

LEEDuser Basic Member

59 thumbs up

Mon, 09/24/2018 - 21:08

Thanks Bill, The quick and frank feedback is greatly appreciated. I'll ask the fabricator if they can calculate the candela/m (nit) data based on light fixtures scheduled....and will proceed as you recommend if that is unsuccessful. I suspect the metric is difficult to calculate or perhaps just new/unfamiliar for many fabricators and manufacturers. As you noted, I only saw reference to nit levels in LED billboard sign websites.

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FAQs about SSc6 :

Exterior internally lit signage - Manufacturer furnished "nit" data, or Design team calculation task?

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