Low-level lighting by electroluminescent diode(s), esp. for steps or stairs, has illuminated zone restricted by optic filters - films giving prismatic and louvre effects

摘要

To give persons approaching warning of steps or stairs, a light source is fixed to the riser which illuminates the approach zone. The source comprises, eg., a horizontal row of diodes (2), emitting light both below and above a horizontal optical axis (A). Characteristically, for the diodes proposed, 85% of the total luminous flux is found within a cone (10) whose sides (R1,R5) are inclined at 15 deg. to the axis. That part of the light whose direction of emission is above the axis is potentially undesirable in this application, as it may dazzle, and cause to stumble, approaching persons. The invention seeks to overcome this, using two optical filters to control the emission. The filters are marketed commercially, in film format, under the trade mark 3M'. One (3), referenced IDF20 11, presents a series of horizontally disposed prismatic striations (15), producing a 20 deg. downward deflection of incident light from the diodes. The other (4), LCF ABRO 30 AG 60, includes a series of opaque, transverse, parallel slats (16), each inclined at 20 deg. Slat spacing and width ensures that, taking account of the prismatic deviation, light emitted upward at angles over 20 deg.(R2) is totally masked, giving a dark zone (20) at tread level, with another (21) below that usefully extends the well-lit area near the step.