# Light-diffusing System: Building Code Definition > How the IBC 2009 define light-diffusing system, where the wording differs, and which chapters depend on the term. - Canonical: https://harth.build/resources/glossary/light-diffusing-system/ - Last updated: 2026-09-07 - Data source: Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control. ## Key facts | Fact | Value | | --- | --- | | Defined in | IBC 2009 (2009 editions transcribed in this corpus) | | Primary source | IBC 2009 Plastic (model text, not a jurisdiction's adopted text) | | Chapters using the term | 2 (counted across the codes hosted here) | | Wording identical across codes | Single code (compare before citing one code's wording under another) | ## Direct answer Light-diffusing system is a defined term in the International Building Code (IBC) 2009, in Plastic. The code's own words are: “Construction consisting in whole or in part of lenses, panels, grids or baffles made with light-transmitting plastics positioned below independently mounted electrical light sources, skylights or light-transmitting plastic roof panels. Lenses, panels, grids and baffles that are part of an electrical fixture shall not be considered as a light-diffusing system.” No other I-Code in this corpus defines it, so the IBC 2009 definition is the one to work from. The term is used in 2 chapters of this corpus, most often in Plastic (IBC 2009), Definitions (IBC 2009). These pages transcribe the 2009 model text; verify the definition against the edition and amendments your authority having jurisdiction has adopted. *Content and cited inputs reviewed by [Scott Barrington](https://nz.linkedin.com/in/barrington), Harth founder and architectural technology specialist · Published 2026-09-07 · Updated 2026-09-07.* ## What does this term mean? **Light-diffusing System** — IBC 2009, Plastic: > Construction consisting in whole or in part of lenses, panels, grids or baffles made with light-transmitting plastics positioned below independently mounted electrical light sources, skylights or light-transmitting plastic roof panels. Lenses, panels, grids and baffles that are part of an electrical fixture shall not be considered as a light-diffusing system. ![Labeled code-term definition diagram: Light-diffusing System: Building Code Definition](https://efwwel0vyt9vy5so.public.blob.vercel-storage.com/images/glossary/light-diffusing-system/diagram-1344.webp) *How the IBC 2009 define light-diffusing system, where the wording differs, and which chapters depend on the term.* ## What must be verified before using this guidance? **Light-diffusing System** is defined once in this corpus, in the [Plastic](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/plastic.md) chapter of the International Building Code (IBC) 2009: > Construction consisting in whole or in part of lenses, panels, grids or baffles made with light-transmitting plastics positioned below independently mounted electrical light sources, skylights or light-transmitting plastic roof panels. Lenses, panels, grids and baffles that are part of an electrical fixture shall not be considered as a light-diffusing system. ## Where light-diffusing system is used in the code The term appears in 2 chapters of the 2009 I-Codes hosted here. The chapters that lean on it hardest are the ones to read next. | Chapter | Code | Mentions | | --- | --- | --- | | [Plastic](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/plastic.md) | IBC 2009 | 10 | | [Definitions](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/definitions.md) | IBC 2009 | 1 | ### The term in use How the code actually writes about light-diffusing system, quoted from the 2009 text hosted here: > In buildings that are equipped throughout with an automatic sprinkler system in accordance with Section 903.3.1.1, plastic light-diffusing systems shall be protected both above and below unless the sprinkler system has been specifically approved for installation only above the light-diffusing system. — [IBC 2009 §2606.7.4](https://harth.build/resources/building-codes/us-states/maryland/ibc-2009/plastic.md) ## The terms light-diffusing system is built out of The definition above leans on 2 other defined terms. Each carries its own code definition, and a local amendment to any of them changes what light-diffusing system covers: - **[System](https://harth.build/resources/glossary/system.md)** — IFC 2009: An assembly of equipment consisting of a tank, container or containers, appurtenances, pumps, compressors and connecting piping. - **[Shall](https://harth.build/resources/glossary/shall.md)** — IRC 2009: The term, when used in the code, is construed as mandatory. ## Light-diffusing System: what to open, and in what order Every row is a document this term depends on. The [ICC code library](https://codes.iccsafe.org/codes) and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) cover the middle rows. | Check | Where | Confirmed | | --- | --- | --- | | Read the definition in the adopted IBC | Plastic | | | Re-check the requirement that uses it | Plastic (IBC 2009) | | | Re-check the requirement that uses it | Definitions (IBC 2009) | | | Confirm the dependent definition | System | | | Confirm the dependent definition | Shall | | | Local amendment to any of the above | Jurisdiction's amendment list | | **A research aid, not a code determination.** The authority having jurisdiction decides which edition and which amendments apply. ## Where can you explore related guidance? - [Explore all glossary guidance](https://harth.build/resources/glossary.md) - [System: Building Code Definition](https://harth.build/resources/glossary/system.md) - [Foam Plastic Insulation: Building Code Definition](https://harth.build/resources/glossary/foam-plastic-insulation.md) - [Plastic, Approved: Building Code Definition](https://harth.build/resources/glossary/plastic-approved.md) - [Plastic Glazing: Building Code Definition](https://harth.build/resources/glossary/plastic-glazing.md) ## Sources and method Definitions quoted from the 2009 International Codes as transcribed in this site's building-codes collection, with the source chapter linked for each quotation. Usage counts are computed over the chapters hosted here, one copy per code. The [ICC code library](https://codes.iccsafe.org/codes) publishes the current model text and the [ICC adoption maps](https://www.iccsafe.org/advocacy/code-adoption-maps/) show which edition a jurisdiction has adopted; those sources control. ### Source links - [codes.iccsafe.org](https://codes.iccsafe.org/codes) - [iccsafe.org](https://www.iccsafe.org/advocacy/code-adoption-maps/) ## Frequently asked questions ### What is the code definition of light-diffusing system? The International Building Code (IBC) 2009 defines it in Plastic as: “Construction consisting in whole or in part of lenses, panels, grids or baffles made with light-transmitting plastics positioned below independently mounted electrical light sources, skylights or light-transmitting plastic roof panels. Lenses, panels, grids and baffles that are part of an electrical fixture shall not be considered as a light-diffusing system.” The 2009 model text is reproduced here; the definition that binds your project is the one in the edition your jurisdiction has adopted, as amended locally. ### Which parts of the code depend on light-diffusing system? In this corpus the term is used across 2 chapters, led by Plastic in the IBC 2009. Those are the sections whose scope moves if the definition is amended locally, so read them together with Chapter 2 rather than on their own. --- - Continue in Harth (open this topic in the Harth agent): https://app.harth.build/agent?context=%2Fresources%2Fglossary%2Flight-diffusing-system%2F - View this page in a browser: https://harth.build/resources/glossary/light-diffusing-system/ - All resources for agents: https://harth.build/llms.txt