A small device shows a green indicator in the renovated room. You want to infer from this that the indoor air is generally unproblematic. Before you interpret the colour so broadly, it must be clear which quantity the device actually measures and what conclusion can be drawn from it. A reading is only understandable in the context of its measurement task.
First read the named measured quantity
CO2 and TVOC are different indications. The Umweltbundesamt explains in the school-related contribution on CO2 traffic-light devices that their colours refer to the carbon dioxide concentration. It treats CO2 there as an indication of the ventilation situation when people are present. [CO2] The source is not a guide to a comprehensive assessment of pollutants in a dwelling.
For TVOC, the Ausschuss für Innenraumrichtwerte explains the sum of volatile organic compounds as an investigative parameter of the overall burden. At the same time it makes clear that the TVOC value alone does not permit a health assessment. [TVOC] That is the central limitation: even a professionally determined sum value is not a complete health judgement.
Do not equate a consumer indicator with a professional measurement
Read the exact model description and note which quantities are described as measured values, estimates or indices. Ask the manufacturer for an explanation if anything is unclear. This article does not examine sensor technology and does not confirm that any household device provides the same information as a professional investigation.
In the fictional example a resident cites a green CO2 reading in response to the question about a new material smell. The parties therefore first assign the measurement task: the colour does not explain the smell. They document the actual anomaly and ask which professional investigation would be suitable for that, instead of trying to answer an unrelated question with a different number.
Formulate the specific decision as a brief
Explain to the specialist why you need an assessment: an unusual odour, a follow-up question about work carried out or another concrete observation. Provide existing product and execution documents as well as the exact device information. The specialist should determine which investigation and which evaluation basis are appropriate for the case.
This article deliberately does not cite limit values or a self-compiled traffic-light scheme. Health complaints belong in separate medical clarification. A laboratory finding should make clear what was investigated and how limited its statement is. It does not constitute an unconditional confirmation of every conceivable characteristic of the room.
Still find a limited result useful
An indicator does not have to explain the entire indoor air to have a useful specific task. What matters is not to expand its meaning. Therefore record, alongside a value, the measured quantity, the origin and the intended inference.
This guidance applies to Germany. The CO2 source stems from a school/pandemic context of 2021; no ventilation intervals, infection protection rates or residential limits are derived from it. The current AIR page is used only for the expressly limited meaning of the TVOC sum value.