This 2D simulator sets up a classic shadow-puppet stage from the side: a lamp on the left, a cutout puppet in the middle, and a translucent screen on the right. Drag the sliders to change how far the light sits from the screen and how far the puppet sits from the light, and watch the projected silhouette grow or shrink exactly as similar-triangles optics predicts — shadow size equals puppet size times the light-to-screen distance divided by the light-to-puppet distance. Switch the lamp from a point source to an extended one and widen its size to see the sharp edge soften into a graded penumbra band around a dark umbra core, with live readouts for magnification, umbra width and penumbra width updating as you adjust every control.