// Vertex shader

...
float dist = distance( vPos, uLightPos ) / 30.0;
// Encode float over multiply bytes for higher accuracy
gl_FragColor = vec4( dist, fract( dist * 100.0  ), fract( dist * 10000.0 ), 1.0 );
...

// Fragment shader

...
// Decode multiple byte float
float lightDist = 0.0;
lightDist += floor( lightSample.x * 100.0 ) / 100.0;
lightDist += floor( lightSample.y * 100.0 ) / 10000.0;
lightDist += floor( lightSample.z * 100.0 ) / 1000000.0;
lightDist *= 30.0;
...