The FCC proposed a fine of $25,000 against a manufacturer of fluorescent lighting fixtures.

Wait a minute. Lighting fixtures? Well, sure, the FCC regulates radio transmitters. And digital devices, which produce radio waves as a by-product that can interfere with communications. But lighting fixtures? Will the bathroom plumbing be next?

In fact fluorescent fixtures are a frequent source of radio interference. We reported on three such cases a few years ago, all making trouble for 4G providers in the 700 MHz band: this order, this one, and this one. In those instances the FCC asked the occupants of premises that used the light fixtures to replace them. Although it is illegal to operate any device that causes radio interference, even a light fixture, the occupants were in no danger of fines or imprisonment if they cooperated.

Everything is more complicated than it seems, even fluorescent lights. They all can malfunction in ways that cause interference, but one category poses a special risk: it intentionally generates radio-frequency energy to excite the gas in the tube and create light. This puts it in a class of devices the FCC calls “Industrial, Scientific, and Medical,” or ISM for short, which use radio waves to change the properties of materials – for example, by heating them. (Microwave ovens are also ISM devices.) The FCC has set aside certain frequency bands in which ISM equipment can produce unlimited amounts of power. The FCC nonetheless regulates these devices for their emissions outside the ISM bands. The procedures are not particularly onerous: testing, labeling and record retention, but no submissions to the FCC. The entire procedure is self-administered. The FCC label indicates the device has been tested for compliance with the limits for radio-frequency emissions, which in turn means the device is unlikely to cause interference.

Apparently, though, a manufacturer of lighting fixtures called Acuity Brands, Inc. did not get the memo. The FCC received reports of interference related to the company’s products and found they lacked the required labeling. The interference itself is not a rules violation, but the missing label is. The company compounded its problems by continuing to sell unlabeled units after hearing from the FCC. The result: a proposed fine of $25,000. Acuity can request a reduction or cancellation.

Nowadays even devices that carry out the simplest functions may have the potential to cause radio interference, leading to trouble with the FCC. To avoid a fine, at the very least, manufacturers should find out whether their products require FCC procedures. Not knowing can become expensive.