LSI Industries Inc. 美股招股说明书（2026年2月25日版）

Filed pursuant to Rule 424(b)(5)Registration No. 333-290202 The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and theaccompanying prospectus are not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offeror sale is not permitted. SUBJECT TO COMPLETION, DATED FEBRUARY 25, 2026 PRELIMINARY PROSPECTUS SUPPLEMENT(To Prospectus dated September 22, 2025) Shares of Common Stock We are offeringshares of our common stock, without par value (“Common Stock”) pursuant to this prospectus supplement and theaccompanying prospectus. The offering price for each share of Common Stock is $. Our Common Stock is listed on The NASDAQ Global Select Market under the symbol “LYTS”. On February 24, 2026, the last reported sale priceof our Common Stock on The NASDAQ Global Select Market was $21.96 per share. Investing in our securities involves a high degree of risk. You should review carefully the risks and uncertainties referenced under theheading“Risk Factors”beginning on page S-5 of this prospectus supplement and under similar headings in the other documents that areincorporated by reference in this prospectus supplement and the accompanying prospectus. (1)See “Underwriting” beginning on page S-10 for additional information regarding underwriting compensation. We have granted the underwriters an option to purchase for a period of 30 days from the date of this prospectus supplement up to an additionalshares of our common stock at the public offering price, less underwriting discounts and commissions. If the underwriters exercise this optionin full, the total underwriting discounts will be $and our total proceeds, before expenses, will be $. Delivery of the shares of common stock is expected to be made on or about Marchconditions. Table of Contents All or a portion of the net proceeds of this offering will be used to implement our growth and acquisition strategy, including (i) payment of aportion of the purchase price for our proposed acquisition of Royston Group (the “Royston Acquisition”) pursuant to the Agreement and Plan of Mergerdated February 20, 2026 among SRR Holdings, Inc. (“Royston”), Rhino Acquisition Company, Inc. (“Merger Sub”), our wholly owned subsidiary, and LSI(the “Royston Merger Agreement”); (ii) repayment of borrowings under a credit facility (the “Credit Facility”) with PNC Capital Markets LLC and PNCBank, National Association (together, “PNC”), which will be amended to increase the amount available under the Credit Facility to $425 million pursuantto that certain Senior Secured Credit Facility Commitment Letter, dated January 21, 2026 between PNC and LSI (the “Proposed Senior Secured CreditFacility”) to be used to fund the purchase price of the Royston Acquisition which is expected to close in the third quarter of fiscal year 2026; and/or (iii) for Neither the Securities and Exchange Commission, any state securities commission, nor any other regulatory body has approved ordisapproved of these securities or determined if this prospectus supplement and the accompanying prospectus are truthful and complete. Anyrepresentation to the contrary is a criminal offense. Joint Book-Running Managers Craig-Hallum Oppenheimer & Co. Table of Contents ABOUT THIS PROSPECTUS SUPPLEMENT This prospectus supplement and the accompanying prospectus relate to the offering of our common stock. Before buying any of the common stockthat we are offering, we urge you to carefully read this prospectus supplement and the accompanying prospectus, together with the informationincorporated by reference as described under the heading “Where You Can Find More Information; Incorporation by Reference” in this prospectus This document is in two parts. The first part is this prospectus supplement, which describes the specific terms of this offering and the securitiesoffered hereby and also adds to and updates information contained in the accompanying prospectus and the documents incorporated by reference into thisprospectus supplement and the accompanying prospectus. The second part, the accompanying base prospectus, dated September 22, 2025, included in ourregistration statement on Form S-3 (File No. 333-290202), along with the documents incorporated by reference therein, gives more general information and If the description of this offering varies between this prospectus supplement and the accompanying prospectus, you should rely on the informationin this prospectus supplement. This prospectus supplement, the accompanying prospectus, any free writing prospectus and the documents incorporated into This prospectus supplement and the accompanying prospectus are part of a “shelf” registration statement that we filed with the Securities andExchange Commission (the “SEC”). Under this shelf registration process, we may offer from time to time various securities, of which this offering of