Lighting of Signs

• Externally illuminated signs can be lit only from the top of the sign, with fully shielded fixtures installed to prevent light spilling beyond the physical edges of the sign (Section 102-5E(1)).

• The luminance level (the amount of light emitted by or from a surface) is limited to 100 candelas per square meter as measured under conditions of full white display (Section 102-5E(2)). (An example of a luminance meter needed to take this measurement can be found here.)

• The illuminated surface area of the sign is limited to 200 square feet (Section 102-5E(3)).

• This lighting also counts towards the total lumens allowed per site (see Section 102-4C(1)).

• The color temperature of the light must be 2700K or less (Section 102-4B) (2400K or less is recommended to be the most dark-sky and neighbor friendly).

• Nonresidential properties: The lights must be turned off within one hour of close of business or operations and can't be turned on more than an hour before opening (Section 102-4D(1)). 

• Residential properties: The lights must be turned off by 11pm unless needed for safety and security (Section 102-4D).

Note that these restrictions are in addition to those adopted by the Historic District Commission. See Chapter 340 the Code of Nantucket (Town Regulations), Section 340-13 ("A sign may be illuminated for a business operating after sunset, provided that the wattage used does not exceed 450 lumens (under a thirty-watt incandescent bulb), is not fluorescent in style, and that the source of illumination shall be shielded and directed downward at the sign.") 

To the extent the HDC regulations and the outdoor lighting bylaw are in  conflict, the more restrictive provision controls. See bylaw Section 102-2B ("In case of a conflict between . . . any provision of [Chapter 102] and another provision of the Nantucket Code, the most restrictive provision shall control.") 

Signs that are illuminated internally (i.e., the light source is within the sign itself, like in this photo of a sign on the mainland) – to the extent they are allowed by the Historic District Commission (see below) – are subject to the same restrictions that apply to externally illuminated signs except they don't have to be lit only from the top of the sign. 

For business signs, the Historic District Commission only allows lighting that is "directed downward at the sign," which suggests that internally illuminated business signs would not be allowed. See Chapter 340 the Code of Nantucket (Town Regulations), Section 340-13 ("A sign may be illuminated for a business operating after sunset, provided that. . . the source of illumination shall be shielded and directed downward at the sign.")