Title 24 Sign Lighting Requirements
An internally illuminated sign is allowed its illuminated area times 12 watts per square foot; an externally illuminated sign gets its area times 2.3 watts per square foot. Signs also have their own controls requirement and their own compliance form, NRCC-LTS-E.
Two allowances, five times apart
The internally illuminated allowance is 12 watts per square foot of illuminated sign area. The externally illuminated allowance is 2.3 watts per square foot. The gap is not an inconsistency — an internally lit box has to push light through a face, while a floodlit panel is lit directly and needs far less power for the same apparent brightness.
For an external sign, only the area lit without obstruction or interference by one or more luminaires counts toward the calculation. A panel that a parapet or a tree throws into shadow cannot be included to enlarge the allowance.
Double-faced signs count one face
For a double-faced sign only the area of a single face is used to determine allowed lighting power. This catches people out on pylon and blade signs, where the instinct is to total both sides. Half the surface, the whole allowance — and a sign sized on the doubled figure will be roughly twice its permitted power.
Outdoor signs have to dim at night
Outdoor sign lighting that is on both day and night needs a dimmer able to automatically reduce sign lighting power by at least 65 per cent during night-time hours. The reasoning is straightforward: a sign readable against daylight is glaringly over-lit once the sky goes dark.
"On both day and night" is defined rather than left open. A sign lit at night and also lit for more than one hour during daylight hours counts as on both day and night. An hour of daytime operation is the line.
Indoor signs need a time switch
All indoor sign lighting other than illuminated exit signs has to be on an automatic or astronomical time-switch control. That covers the lit menu board and the window sign as much as anything architectural, and it is regularly the item missing from a retail fit-out submittal.
Large message centres also do demand response
An electronic message centre with a new connected lighting power load above 15 kW needs a control capable of reducing lighting power by at least 30 per cent when it receives a demand response signal, under the code's demand management requirements. This is a genuinely large display — a stadium board or a highway-scale screen — not a shopfront panel.
What sits outside all of this
Exit signs and traffic signs are not assessed under the sign lighting allowances; they meet the Appliance Efficiency Regulations instead. Unfiltered incandescent lamps that are not part of an electronic message centre or an illuminated sign are also outside it.
The dimming requirement has its own exceptions: outdoor signs in tunnels, and signs in large permanently covered outdoor areas that are intended to be lit continuously, 24 hours a day and 365 days a year. Both describe places where there is no night-time condition to dim into.
It is a separate submittal
Sign lighting is documented on its own forms rather than folded into the indoor or outdoor lighting set: NRCC-LTS-E for the certificate of compliance and NRCI-LTS-E for the certificate of installation. A project with a lit sign and no LTS forms is incomplete even where the indoor and outdoor lighting is fully documented.