I would argue that the spells have full effect. I think it would need to have text like Daylight to be blocked.
You touch an object when you cast this spell, causing the object to shed bright light in a 60-foot radius. This illumination increases the light level for an additional 60 feet by one step (darkness becomes dim light, dim light becomes normal light, and normal light becomes bright light). Creatures that take penalties in bright light take them while within the 60-foot radius of this magical light. Despite its name, this spell is not the equivalent of daylight for the purposes of creatures that are damaged or destroyed by such light.
If daylight is cast on a small object that is then placed inside or under a light-proof covering, the spell’s effects are blocked until the covering is removed.
Daylight brought into an area of magical darkness (or vice versa) is temporarily negated, so that the otherwise prevailing light conditions exist in the overlapping areas of effect.
Daylight counters or dispels any darkness spell of equal or lower level, such as darkness.
However, I imagine that others may say that Umbral Shield could protect against the death effect of the spells.
The subject ignores any harmful effects of bright light or sunlight for 1 minute. The mesmerist can trigger this trick whenever the subject would be exposed to harmful bright light (such as sunlight is to a vampire). The subject is immune to the dazzled condition while this trick is in effect.
If one can infer that the harmful effects from sunburst and sunbeam come from the bright light itself, then umbral shield would prevent it from affecting the mesmerist. If not, then it would only protect the mesmerist from the parts of the spell that do extra damage to those vulnerable to bright light/sunlight.
I subscribe to the first interpretation--no light, no damage, no blinding.
Isn't Umbral Shield a trick that's available at level 1 to a Mesmerist? A lvl 1 trick is more powerful than lvl 7 and lvl 8 spells?
'bright light' and 'sunlight' in Pathfinder have specific meanings.
Most creatures don't take any damage from either of course. In creature that normally would take damage from either of those to game turns would be protected by umbral shield from that damage.
Sunbeam is described as 'intense light' (not either bright light or sunlight) and Sunburst is 'searing radiance' (also not mentioned by Umbral shield.)
Umbral shield does what it says it does, it protects against the specific conditions of bright light and daylight, nothing more. It offers no protection from either of these spells.
Note that Umbral Shield also doesn't change the creature so it is isn't harmed by sunlight etc, is simply lets them ignore those harmful effects for a period of time. As such any riders that add damage and such to creatures that are harmed by sunlight would still effect those creatures (double damage etc.).
And a 3rd level paladin ability, aura of courage, defeats weird, a 9th-level spell castable at character level 17 at the earliest. Ability acquisition level is a risky metric to use for deciding rules interactions.