Скачать или смотреть How To Make Handheld Torch Lighting Using Command Blocks

First Command:

execute as @a at @s anchored feet run fill ~-4 ~-4 ~-4 ~4 ~4 ~4 air replace minecraft:light

| repeat | unconditional | always active |

Second Command:

execute as @a[nbt={SelectedItem:{id:"minecraft:torch"}}] at @s run fill ~ ~1 ~ ~ ~1 ~ minecraft:light replace air

| chain | unconditional | always active |

Third Command:

execute as @a[nbt={equipment:{offhand:{id:"minecraft:torch"}}}] at @s run fill ~ ~-1 ~ ~ ~1 ~ minecraft:light replace air

| chain | unconditional | always active |

You can change the light level by writing: minecraft:light[level:(0-15)]
If you want you can keep adding chain commands and you can do different items and different light levels. You could do glowstone and make it be light level 10 or something.