This note introduces the photogravitational index (Φ) as a dimensionless parameter for classifying stellar structure by the balance of radiation and gravity. Defined Φ = L / (M × a) it enables comparison across stellar types. Using TIC catalog data, we computed Φ for 20 stars (see Table 1). A clear correlation between Φ and luminosity is shown in Figure 1. High Φ values reflect radiative dominance, while low Φ values indicate gravitational compression. This supports Φ as a continuous, physical classifier for stellar structural states. ---