Prism Knight

 A Prism Knight is somebody who has figured out that light is a participant in any battle and has trained to use the light to aid them in battle. They can bend light around themselves to create a form of invisibility. They can use light to deceive or blind their enemies. They can even move fast like light.

Refractal Invisibility

Beginning when you choose this archetype at 3rd level, you learn the ability to hide by bending light around yourself, making yourself harder to see. You are able to hide whenever you are in bright light. You also have advantage on stealth checks made in bright light.

While in bright or dim light, you can spend an action to bend light around yourself to gain a form of invisibility. While in this form, a creature can not see you unless they make a successful Wisdom (perception) check. The DC for this check equals (8+ your Dexterity modifier+ your proficiency) and the enemy can make the check with advantage in dim light. Before making an attack against an enemy that can not see you, make a Dexterity check. The DC equals (10+ the target's Wisdom modifier [minimum of 0]) and you have disadvantage on this roll in dim light. On a success, you have advantage on the attack roll. On a failure, the enemy can see you and you make the attack roll normally. You can use this ability a number of times per long rest equal to your proficiency modifier. This ability lasts for 10 minutes or until you enter darkness.

Prism Blade

Starting at 7th level, you can absorb and bounce light from your weapons. Once per day, you can lay your weapons in bright light for 1 hour to absorb light. For the rest of the day, your weapon can emit 10 ft of dim light and you may choose to deal radiant damage with attacks using that weapon instead of the weapon's normal damage type. At 16th level, the dim light becomes bright light.

Once per turn, you may add 1d6 radiant damage to a weapon attack that deals radiant damage. This die becomes a d6 at 10th level, a d10 at 14th level, and a d12 at 18th level.

Images of Light

At 10th level, you can bend light to create illusions of yourself. You can cast the spell Mirror Image a number of times per day equal to your proficiency modifier. You can only do this in bright or dim light.

Blinding Radiance

Starting at 15th level, you gain the ability to blind enemies with your attacks. Once on your turn, when you hit an enemy with a weapon attack that deals radiant damage, you can force the target to make a Constitution saving throw (DC equals 8+ your proficiency bonus+ your Constitution modifier). On a failure, the enemy is blinded until the beginning of your next turn. You can use this ability 3 times per short or long rest.

Lightspeed

At 18th level, the light around you can bolster your speed. You can no longer be targeted by opportunity attacks in bright or dim light. In bright light, your speed increases by 20 ft and you can move across gaps up to 20 ft long. In dim light, your speed increase by 10 ft and you can move across gaps up to 10 ft.