This may refer to a specific kit number or a series designation. For instance, some Polar Lights automotive kits are in the 1:25 scale, and "109" often appears in product codes.
To help you get for your purpose, could you clarify: polarlights casey set 109 25 upd
It seems you are referencing a specific document or case study titled — possibly related to a technical report, a lighting or optics project (given "polar lights"), or an internal case file. This may refer to a specific kit number