By default, A-Frame scenes inject default lighting, an ambient light and a directional light. These default lights are visible in the DOM with the data-aframe-default-light attribute. Whenever we add any lights, A-Frame removes the default lights from the scene.
<!-- Default lighting injected by A-Frame. -->
<a-entity light="type: ambient; color: #BBB"></a-entity>
<a-entity light="type: directional; color: #FFF; intensity: 0.6" position="-0.5 1 1"></a-entity>