of the inside panels 14 are received on pads 28 which engage the outer surface of wall 24 the edge portion of each outer panel is spaced outwardly from the edge portion of each inner panel by a spacer 30 which is interposed between the panel edges a plurality of internally threaded bosses 34 are formed integrally on the outer wall 24 of extrusion 18 a bolt 36 extends through a rigid retainer plate 38 and is threaded into each boss 34 the bolt head is received in a cavity formed in the retainer plate 38 which overlies a pair of pads 40 which fit against the edge portions of the outer panels 14 when the bolts 36 are tightened the retainer plate 38 clamps pads 28 and 40 against the panels 14 with the spacers 30 sandwiched between the edges of the panels in the double glazed arrangement in this manner panels 14 are secured to and supported generally edge to edge on the structural member 16 a cover 42 may be secured to the retainer plate 38 in order to enclose the cavity and cover the bolt heads contained therein the single glazed system is similar but lacks the second set of panels and the spacers 30 in accordance with the present invention the inner edge portion of one or more of the extrusions 18 may be provided with a channel 44 which opens inwardly and extends along the entire length of the extrusion 18 the channel 44 provides a recess in which a neon filled glass tube 46 may be contained and enclosed the glass tube 46 is an elongated hollow tube held in place in channel 44 by a plurality of clips which are.