How does one understand the elements of the Pure Octad in Sunlight? According to Abhidhamma, the smallest unit of Rupa is called the Suddhashtaka(Pure Octad) which has the following 8 elements:

patavi, apo, tejo, vayo, vanna, gandha, rasa, and oja

Regarding Sunlight, the tejo(heat) and the vanna(color) elements seem obvious, but how does one understand others? 

From a Vipassana point of view, is this problem occurring because the mind is getting stuck at the concept of Sunlight?
Buddhism focuses on spiritual development, so the Buddhist analysis of rūpa focuses on sense objects, the sense organs and the body. Non-living things are made up of temperature-born pure-octad groups or temperature-born sound groups. The relevance of non-living things in the Buddhist analysis of rūpa is that non-living things are sense objects.

I would say that sunlight itself does not impact the sense directly, only indirectly. When sunlight bounces off a speck of dust or a wall, then we “perceive” the sunlight through the eye sense. When sunlight makes our skin warm or a rock warm, we “perceive” sunlight through the tactile sense.

The speck of dust, the wall, the skin and the rock… all of these are “non-living things” and are temperature-born pure-octad groups (the eight rūpa that you listed above). They are all to be understood as sense objects. 

Using fire-element (tejo) as one example, some sense objects have greater intensity of the fire-element and will be “warmer” to the tactile sense than other sense objects with less intensity of the fire-element, but all sense objects include the fire-element rūpa. The other seven rūpa in the temperature-born pure-octad group can be seen in a similar way... always present, but with different intensities.