What are the differences between indoor and outdoor-rated lightboxes?

Q: What are the differences between lightboxes for backlit graphics display, that are designed for use indoors or outdoors?
A: The easiest way to characterize the differences between indoor and outdoor lightboxes, is to discuss outdoor-rated models, because almost all the differences occur as “upgrades” to make a lightbox outdoor-capable. So here is a list of features that distinguish outdoor models:
ALUMINUM FRAME. Indoor lightboxes can be made of plastic, steel, aluminum or other products; whereas outdoor lightboxes are usually made of aluminum for both durability and anti-oxidation (rust).
FULL UL LISTING. Most building codes require that any electric sign (including backlit lightboxes) that is to be permanently installed outdoors, must be fully UL-approved as an electric sign. This means that product that only contains UL-listed components does not qualify for outdoor installation, unless the finished, complete lightbox comes with its own UL certification, in the form of an external, serialized sticker stating such.
WEATHER STRIPPING. Ask your lightbox vendor if the outdoor model you’re considering includes weather stripping to seal the enclosure, to minimize interior moisture and contamination.
DRAIN HOLES. Even a well-sealed lightbox needs drain holes at the bottom of the frame to allow excess moisture to escape from the light chamber.
UV-RESISTANT LENS. Not all outdoor-rated lightboxes include UV-resistance at the display face, and even those that do, can’t fully eliminate any UV impact to your graphics, but this can be another option to ask for, with many outdoor models.
CLEAR POWDERCOAT FINISH. Even if you want your lightbox to be silver or aluminum color, ask about a clear powdercoat to protect your aluminum frame. Even though aluminum won’t rust, it can “white” with age, resulting in a possibly undesirable look, which a clear powdercoat will forestall for many years.
HARD-WIRING. Some building codes require that outdoor-installed electrical signs be hard-wired, which means the electrician brings the source wiring all the way to the interior of the lightbox and terminates directly with the lightbox’s internal wiring, instead of via a plug and socket.
EXTRA SPACE BETWEEN FRONT CLEAR LENS AND WHITE DIFFUSER LENS. Even the tightest outdoor lightbox can develop internal condensation, mainly because air always contains a certain amount of water and then as the temperature drops, the moisture in the air will condense onto the surfaces inside the lightbox. For this reason, it is important with outdoor-rated lightboxes, to allow an extra space between the front clear lens and the white diffuser lens, so that condensation can dissipate over time. Not all outdoor models have this feature, but well-planned models do. This extra space will serve to help your graphics perform better longer, with less visual impairment resulting from condensation.
EXTRA INTERNAL BRACING. For areas with severe climate exposure, some outdoor lightbox models can be configured with internal reinforcing poles for extra rigidity.
SECURITY ACCESS. Outdoor applications experience increased likelihood of unauthorized access attempts, so tamper-resistant screws or key locks are optionally available on some outdoor lightbox models.
POLYCARBONATE LENSES. Standard lightbox lenses are usually made of acrylic, commonly known as Plexi-glas (plexiglass). But polycarbonate, though more expensive, yields greater shatter- and crack-resistance by a significant factor. Also polycarbonate lens stock is available in much larger sizes than acrylic, which means a larger display. (Acrylic lens stock typically maxes out at 10-foot lengths, and polycarbonate, depending on the thickness, can be 12 feet to 100 feet maximum length.)
“NO-GLARE” OR GLARE-RESISTANT LENSES. Some outdoor applications benefit from a glare-resistant clear front lens, in order to more effectively display their messages, depending on the environment and type of lighting.
Some indoor models may contain one or more of these normally “outdoor-only” features, but the goal is usually to only order (and of course, invest in) features that will help your backlit display lightboxes perform as needed in the environment for which they are being purchased, and outdoors is clearly the more demanding environment in almost all circumstances.
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