Build a flare from a light source
Set Flare X and Flare Y over the brightest point already in the picture. A flare anchored to a real light source reads as optics; one floating over a shadow reads as a sticker.
Intensity and Halo size control the glow around the source. The halo falls off as an inverse power rather than as a bell curve, which is what gives real glare its long tail, and the light is added on squared channel values so the core reaches white without washing the midtones out first.
Veiling glare
Not all the scattered light lands near the source. Some of it bounces around the barrel and settles over the whole frame, lifting the blacks and flattening contrast in the region nearest the light.
That wash is what makes a photograph look like it was taken into the sun. Intensity drives it alongside the halo, so raising one raises the other and the flare stays attached to the image instead of sitting on it.
Starburst spikes and aperture blades
Spikes appear when a lens is stopped down to a small aperture. Light diffracts around the blade edges and paints a line for each pair of blades, which is why street lamps in night photography show clean stars at f/16 and none at f/1.8.
The count sets the shape twice over. A 6-blade aperture draws 6 spikes and also stamps its 6 sides onto the ghosts, because both come from the same opening. At 0 the blades read as retracted, so the ghosts go round and the spikes disappear.
Ghosts follow the frame centre
The ghost pair is not decoration placed at random. Light entering off-axis reflects between lens elements and lands on the sensor along a predictable line: from the source, through the optical centre, and out the far side.
A source in the top left throws its ghosts down and to the right, and a source near the centre collapses them into a short run. There are 2 of them because a modern coated lens throws about that many with any strength. A long chain of matched pastel discs belongs to plugin presets, not to glass.
Example: backlit portrait
Place the source just outside the subject’s shoulder at roughly 22% across and 20% down, set Intensity near 50, Halo size near 16, and Warmth around 30 to match late sun. Keep spikes at 6.
Then check the ghosts: if one lands over a face, nudge Flare X a few percent rather than dropping Intensity. They shift along their axis and usually clear the subject without weakening the flare.
Where flares stop being believable
A flare is added light, so it can only brighten. Adding one over a dim, evenly lit interior gives a glow with no source to justify it.
Intensity above roughly 80 pushes a wide area of the frame to white and the core loses its gradient. Check the exported file at full size before publishing it, since the preview runs at up to 1200px and small clipped areas are easier to miss there.