# lt\_nonalg The light extinction coefficient, $$k\_l$$, is calculated as a function of the algal density using the nonlinear equation: $$k\_l=k\_{l,0}+k\_{l,1}*\alpha\_0*algae+k\_{l,2}*(\alpha\_0*algae)^{2/3}$$ where $$k\_{l,0}$$ is the non-algal portion of the light extinction coefficient ($$m^{-1}$$), $$k\_{l,1}$$ is the linear algal self shading coefficient ($$m^{-1}(\mu g - chla/L)^{-1})$$, $$k\_{l,2}$$ is the nonlinear algal self shading coefficient $$m^{-1}(\mu g - chla/L)^{-2/3})$$, $$\alpha\_0$$is the ratio of chlorophyll *a* to algal biomass ($$\mu g$$ chla/mg alg), and $$algae$$ is the algal biomass concentration (mg alg/L). #### Relevant chapter in the Theoretical Documentation: [Local Specific Growth Rate of Algae](/io-docs/theoretical-documentation/section-7-main-channel-processes/in-stream-nutrient-processes/algae/algal-growth/local-specific-growth-rate-of-algae.md) --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://swatplus.gitbook.io/io-docs/introduction-1/channels/nutrients.cha/lt_nonalg.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.