How to create lightable box?

I've created a bottomless box with vertices, but it doesn't receive vertex lighting. The following is an example with 2 lights, my vertex box, and a Blitz cube. I want the box to be shaded like the cube. Using UpdateNormals() creates...splodgy shading.

Graphics3D 1024,768,32,0
pivot=CreatePivot()
camera=CreateCamera(pivot)
PositionEntity camera,0,5,-10
PointEntity camera,pivot

AmbientLight 120,120,120
light1=CreateLight()
LightColor light1,40,100,255
TurnEntity light1,45,-205,0	
light2=CreateLight()
LightColor light2,255,230,180
TurnEntity light2,45,35,0	
	
mdl_block=CreateMesh()
block_surface=CreateSurface(mdl_block)
vA=AddVertex(block_surface,-1,-1,-1)
vB=AddVertex(block_surface,-1,-1,1)
vC=AddVertex(block_surface,-1,1,-1)
vD=AddVertex(block_surface,-1,1,1)
vE=AddVertex(block_surface,1,-1,-1)
vF=AddVertex(block_surface,1,-1,1)
vG=AddVertex(block_surface,1,1,-1)
vH=AddVertex(block_surface,1,1,1)

AddTriangle (block_surface,vA, vC, vD)
AddTriangle (block_surface,vA, vD, vB)
AddTriangle (block_surface,vB, vD, vH)
AddTriangle (block_surface,vB, vH, vF)
AddTriangle (block_surface,vF, vH, vG)
AddTriangle (block_surface,vF, vG, vE)
AddTriangle (block_surface,vE, vG, vC)
AddTriangle (block_surface,vE, vC, vA)
AddTriangle (block_surface,vC, vG, vH)
AddTriangle (block_surface,vC, vH, vD)

brush=CreateBrush()
BrushColor brush,255,255,255
BrushFX brush,0

PaintEntity mdl_block,brush
FlipMesh mdl_block
PositionEntity mdl_block,-2,0,0

cube=CreateCube()
PositionEntity cube,2,0,0

While Not KeyHit(1)
	If KeyDown(205)
		TurnEntity pivot,0,1.0,0
	ElseIf KeyDown(203)
		TurnEntity pivot,0,-1.0,0
	EndIf
	If KeyDown(200)
		TurnEntity pivot,1.0,0,0
	ElseIf KeyDown(208)
		TurnEntity pivot,-1.0,0,0
	EndIf
	RenderWorld
	Flip
Wend

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