The Burst

I wouldn't mention it if I were you. The quickest way to garner Light's wrath is to show him this symbol.
You see, he doesn't think it highlights his strengths, but his weakness. He wanted to kill everyone that day, and he succeeded. Innocent or not, all fell to his wrath because he could not tell the difference. He ended up inheriting the mantle and title of Light for his terrible deed, an act the previous Light should have condemned him for.
The burst is a reminder, he does not deserve his charge.

--Leeyal, owner of the Dark Light Tavern, Selaserat

Research:

The Evenacht Pact

by our melancholy hero,
Lorgan the Thoughtful

In this Research Document:

all images by Shade Melodique
unless otherwise stated

The Burst Iconography

I would hazard the Burst is probably the second most well-known religious symbol of the syimlin, right behind Sun's Sunrise/Sunset.
The Burst is usually found with offering bowls or small altars, where the star-like burst collides with the aforementioned object. The older incarnations of the symbol have three points that curve out like leaves on either side, with a tall stem jutting high, sometimes reaching the ceiling of a religious alcove or small room. It resembles a golden flower without the petals.
The burst and stem have changed over the years, and modern Talis acolytes burn a myriad of thin wires into a golden circle's edges, which then stick out in all directions. These wires vary in length, and the top ones wrap around the stem. The stem is column-like, with flutes.

Origin

Before Talis became a syimlin, he was a Light-blessed in the Aristarzian Light Temple. The Aristarzians brought all boys born with red hair and blue eyes to the temple to train them to be Light's representative on the continent of Faeyim. The training, called the Gauntlet, killed most of them at incredibly young ages.
The head priest would gift those who survived a crown with gemstones that stored magic energy. The crown represented Light's might, and the man who earned it spent the remainder of his days as the most respected human in Aristarzia.
Talis defeated the Final Gauntlet. A friend crowned him since the high priest could not pull himself from his shock to do so. Upon acquiring it, he and his fellow Light-blessed fought their way to the Light-ascended's throne.
Talis used the power in the gems to propel himself into the air, then race down to the throne, Light-fast. The power in the crown struck the power in the throne, and the explosion obliterated the temple and the city of Elistenye. For destroying the corrupt, Light gifted Talis his mantle and title, and the newest Light-ascended became the Syimlin of Light.
The Burst symbolizes the race down and the explosion that followed the impact of crown and throne, ridding the Aristarzian of an evil that guided their culture for millennia.

Red and the Light-blessed in Selaserat refuse to speak on it, and the religious texts don't say, how Talis survived the explosion. He had just finished the Final Gauntlet, a trial that drained strength, stamina and magic. He should have turned into a pile of ash which, in turn, disintegrated under the rest of the explosion. Instead, he survived to become Light.
I've been cautioned not to ask Red about it. He's the avatar of Light, he should know, but I think it's a sore spot, not only because he harbors hate for the Aristarzian and their centuries of religiously sanctioned torture, but because Talis hates that his most destructive act led to his divinity.

Use

The Burst, while representing an act by a human, is held most sacred by the elfines. It is a common pattern in their religious regalia no matter which syimlin they serve, and they have ceremonies surrounding the holy deed.
Light, for elfines, is the second highest-ranked syimlin, behind Sun. It was that way for centuries, for Talis's predecessor, Dresharen, was an elfine. They continued their intimate worship of Light because Dresharen gave Talis his blessing and title.
Elfines most often depict the Burst with an offering bowl surrounded by candles. The room in which it sits has tapestries that follow Talis's childhood to his ascension, ending with the destruction of the Temple in, you guessed it, a burst of light.

There are other symbols of Light: the crown, yellow gemstones, and Talis's singing voice. Most of the iconography in the primary Light temple in the Evenacht, The Blinding Shadows, has candles.
I'm under the impression he has a fondness for destroying the Dryanflow barrier Kjiven places across the river. I'm sure an industrious sort will eventually come up with an image others will like enough to use.