How to prevent Armour Stand equipment and passengers from turning black when entering a block

I'm in Java 1.14.4 and I'm trying to create a gate out of iron bars, that slides open and closed, smoothly.

I have /summon minecraft:armor_stand ~ ~ ~ {Tags:["gate"],NoGravity:1b,Passengers:[{id:"minecraft:falling_block",NoGravity:1b,BlockState:{Name:"minecraft:iron_bars",Properties:{east:"true",west:"true"}},Time:-2147483648,DropItem:0b}]}Which is a falling block iron bar riding an armour stand.

I'm using execute as @e[tag=gate] at @s run tp @s ~ ~0.053 ~ to teleport the armour stand up and down to create a sliding gate. However, the issue is that when the armour stand goes into a block, the iron bar will turn black.

I've tried setting both the armour stand and falling block on fire so the lightning remains bright with execute as @e[type=falling_block] run data modify entity @s Fire set value 2000 but this doesn't work.

You can't. Entities always have the light level of the block they're in.

You could alternatively use minecarts with a DisplayTile and a huge offset, that way you can put them into a well lit room way lower. But then the blocks are slightly smaller than a full block, maxing that you need to use more for the same width and that it's visible that you're not using real blocks.