Type 4 / Category 4 safety light curtains to IEC 61496-1 dominate new construction-machinery guarding, with standard resolutions of 14 mm (finger), 30 mm (hand) and 300/400 mm (body/access), per AutomationDirect's 2026 Datalogic/Contrinex/ReeR/Datasensing range [S1][S4].
For construction environments, IP 69K sealed columns and rugged through-beam single-beam barriers (10–65 m) are the main alternatives when dust, wash-down or outdoor exposure is in play, and EX-rated variants exist for hazardous-area zones [S1][S2].
Resolution tier drives the detection target and the price band
14 mm finger-protection curtains on the AutomationDirect line are sold as sender/receiver pairs from $503.00, reach 10 m operating range, and ship in protective heights up to 1290 mm; the 30 mm hand-protection tier drops to $482.00 per pair and extends range to 20 m with heights to 1822 mm [S4]. Body/access-control curtains at 300 or 400 mm resolution go the other way on range (up to 70 m) but stay shorter in height (up to 1232 mm) and start at $654.00 per pair [S4]. The 14 mm tier is the right pick when operators routinely reach into a hazard point; the 30 mm tier covers whole-hand entry at perimeter guarding; the 300/400 mm tier is access control only, not point-of-operation guarding.
IEC 61496-1/-2 is the framework that defines these Electro-Sensitive Protective Equipment (ESPE) categories, with Type 4 / Category 4 requiring redundant, monitored optoelectronic paths and fault-tolerant output (OSSD) stages [S1][S4]. Within the ifm OY family, OY0 reaches 0–10 m, OY4 0–7 m, and OY8 0–6 m, all to safety category type 4 per IEC 61496, with the OY4 offered in IP 69K protective-tube packaging for steam and high-pressure cleaning environments [S1].
Range, height and beam count: matching the geometry of the site
Operating range is set by sender-to-receiver distance, not by protected height. DirectIndustry lists 190 safety light curtain products split across multibeam (150), single-beam (27) and unspecified (13), with through-beam (143) the dominant configuration, followed by reflex (9), frame (7) and fork (4) [S1]. For long perimeter runs on a site, multibeam through-beam units such as the SICK SLC series cover 5–65 m with resolutions from 14 mm and protection field heights to 1200 mm; for very long single-axis access lines, single-beam barriers like the SLA series run 10–65 m [S1].
Schmersal's SLB 240 safety light barrier delivers 15 m range in a compact metal enclosure with M12 connector and OSSD outputs rated to PLc per ISO 13849-1, with automatic or restart interlock [S1]. SICK's WSU/WEU26-3 rugged single-beam through-beam switch extends access protection to hazardous-area machine perimeters with self-testing sender/receiver, reaching 70 m operating range on infrared [S2]. The KEYENCE GL-R series tops out at 15 m maximum operating distance in a slim, robust housing aimed at harsh industrial environments [S5].
Construction-site hazards: dust, weather, impact, muting
Construction sites impose four stresses a light curtain must survive: airborne dust, mechanical impact, water ingress, and frequent legitimate material passage. IP 69K-rated protective tubes (ifm OY4) and protective columns (AutomationDirect accessory line) address impact and wash-down, while mirrors let a single pair of sender/receiver units protect multiple sides and reduce hardware count on awkward site layouts [S1][S4]. Muting arms and sensors are listed as part of the same accessory ecosystem to allow conveyors or lifts to pass material through the field without tripping the safeguard [S4].
For explosive or hazardous-area zones (e.g. near fuel storage, solvent pumps, or grain-handling plants), Schmersal's EX-SLC/SLG440 extends the optoelectronic protective-device line into Ex-rated designs, and SICK's WSU/WEU26-3 is explicitly positioned as "rugged, for hazardous areas" with self-testing sender/receiver electronics [S1][S2]. These are the right references when the safety light curtain is being installed near a classified zone rather than on a benign factory mezzanine.
Selection criteria matrix: Type 4 curtain vs single-beam barrier vs EX-rated unit
On four decision criteria relevant to construction sites, the three principal device classes line up as follows. (1) Detection target: Type 4 multibeam at 14/30 mm detects finger/hand; 300/400 mm detects body only; single-beam barriers detect any opaque object crossing one axis, with no resolution figure in mm. (2) Typical range: Type 4 hand/finger curtains 10–20 m, body curtains up to 70 m, single-beam barriers 10–70 m, SICK WSU/WEU26-3 to 70 m [S1][S2][S4]. (3) Ingress/robustness: finger/hand curtains sold as standard and slim profiles; ifm OY4 in IP 69K tube; SICK WSU/WEU26-3 and Schmersal EX-SLC/SLG440 for hazardous/Ex areas [S1][S2]. (4) Price floor (USD, sender/receiver pair): $482.00 (30 mm hand), $503.00 (14 mm finger), $654.00 (300/400 mm body) [S4]. The lower price on 30 mm vs 14 mm reflects housing length, not safety category, and either tier remains Type 4 / Category 4 [S4].
The KEYENCE SL-C series, now listed as discontinued on KEYENCE's European site in March 2026, covered both standard-pitch and fine-pitch safety light curtains and has been superseded within the GL-R / GL-S family for new designs [S3][S5]. For builders' hoists, material lifts and mobile plant where the field of protection must follow the moving element, see the broader safety light curtain reference and the matched accessory ecosystem for construction tools guarding on site.
Installation, commissioning and standards hooks
Commissioning checks on a Type 4 / Category 4 install follow the same pattern across vendors: verify OSSD output state, test the muting sequence if used, validate the protective height covers the hazard reach, and confirm the response time is shorter than the machine stop time calculated from the safety distance formula. SICK's C4000 Advanced documentation lists restart interlock, external device monitoring, beam coding, fixed/floating blanking, reduced resolution, PSDI mode (with UE402), bypass (with UE402) and operating mode switching (with UE402) as configurable functions on a 48 mm × 40 mm housing cross-section [S6]. These features matter on construction plants because floating blanking allows small debris to pass without nuisance tripping, while reduced resolution lets a curtain tolerate a partial obstruction during a lift cycle.
Safety category 2 devices to IEC 61496 are still offered (e.g. ifm OY0 covers both categories 2 and 4 in one housing), but for new construction-machinery guarding, the spec baseline has settled on Type 4 / Category 4 because of the redundant, monitored architecture and OSSD outputs that downstream safety relays and PLCs can sink directly [S1][S4]. The SICK WSU/WEU26-3 datasheet specifies "single-beam, through-beam, access control" function with infrared optics, which positions it as a perimeter access switch rather than a point-of-operation finger guard [S2]. For multi-sided perimeter layouts on a site, mirror columns and SLG/SLC light grids are the practical way to fold a 90° or 270° hazard into one pair of sender/receiver units, an approach documented across both the SICK and Schmersal ranges [S1][S6].
Who the light curtain is for, and where it is the wrong tool
A safety light curtain is the right pick when the hazard is a mechanical motion (press, shear, robot cell, conveyor, hoist) and the operator needs frequent, open access rather than a hard guard. It is the wrong tool for: (a) hazards above ~2 m where a fixed guard is cheaper, (b) hazards where the operator must reach over or around the field, defeating the detection plane, and (c) outdoor tower-crane or roofing work where the working plane is not a fixed vertical line. For scaffolding, façade and glazing work the correct reference is the glass curtain wall and metal curtain wall panel guarding guidance, not an ESPE. The door, window and curtain wall encyclopedia entry covers perimeter access on occupied buildings, where a different sensor family applies. [S4]
Fire-safety integration is a separate scope: light curtains are an operator-presence device, not a fire detector, and they do not substitute for the fire safety detection and suppression chain required on most construction sites. On a procurement signal front, public 8-K and SEC filings reviewed on 2026-08-19 do not move the safety light curtain specification itself; what they do is adjust the capex envelope for the procurement signal on building materials which in turn affects how many new guarded machines a contractor is willing to spec in the next build cycle.
Trackable signals to watch after spec
Three signals are worth tracking once a Type 4 curtain is on order. First, confirm the vendor's IEC 61496-1/-2 test certificate is dated within the last five years, not just the model number; older certificates do not always cover the current firmware revision. Second, log the measured response time on commissioning, because a safety-distance recalculation is required if the downstream safety relay or hydraulic stop valve changes. Third, record the muting sequence and lockout/tagout procedure in the site's construction tools method statement, since a correctly specified curtain is only as safe as the bypass logic that contractors actually wire in the field. [S1]