After Dark, a Green Mark: Using a Laser Landing Point for Night Work and Exclusion Zones

▌  APPLICATION NOTE  ·  OCTOBER 2026  ·  NIGHT WORK AND EXCLUSION ZONES

After Dark, a Green Mark: Using a Laser Landing Point for Night Work and Exclusion Zones

Tower crane work does not stop when the light goes. On a night shift the crane keeps lifting, but the crew's eyes are working with less information. Depth cues flatten, colours fade to grey, and the hook becomes a small dark shape against a dark background. The final metre of a lift, which is already the hardest part of the job in daylight, becomes harder still. Everything the crew does after dark has to make up for the light that is no longer there, and the last metre is where that shortfall shows up first.

A tower crane laser positioning system helps at night for a simple reason: it is a light source of its own. The ZNAQ-JG1 mounts on the trolley and projects a vertical 532 nm green beam straight down onto the ground, so a bright green spot marks the hook landing point in the dark just as it does by day. Because the beam is visible, the same mark that shows the crew where the load will land also shows everyone on the deck where the crane is working, which is a useful thing to know when the deck is unlit. Night lifting is governed by the usual framework, with standards such as ISO 12480-1, BS 7121 and LOLER 1998 in play, and in the United States OSHA 29 CFR 1926 Subpart CC; a positioning aid supports those rules, it does not replace them.

01  WHY NIGHT WORK CHANGES THE LAST METRE

Daylight gives a crane crew an enormous amount of information for free. The eye reads the distance to the hook, the angle of the load, the depth of the deck and the position of the next obstruction without being told. At night most of that is gone. Portable lighting throws hard shadows, and a shadow can look like a gap or a ledge. The hook itself may be visible only as a silhouette, and the crew loses the reference points that make a landing point obvious when the sun is up.

The consequence is that the last metre becomes a negotiation again. The signalman cannot simply read the position, and the operator cannot simply see where the hook is heading. Commands get repeated, lowering slows down, and the load hangs over the deck for longer than it needs to. A landing-point marker that is visible on its own is one of the simplest ways to put a reference back into that scene, because it does not depend on the lighting around it; it is the lighting.

▌  NIGHT HIDES THE HOOK  With less light the hook becomes a silhouette, and the crew loses the depth cues that daylight provides for free.

▌  SHADOWS MISLEAD  Portable lighting throws hard shadows that can look like a gap or a ledge rather than a flat surface.

▌  A LONGER LAST METRE  Without a fixed reference, commands repeat and the load spends longer hanging over the deck.

02  WHAT THE GREEN BEAM SHOWS AFTER DARK

The ZNAQ-JG1 projects a vertical green beam from the trolley onto the ground. At night that beam is at its clearest: a 532 nm spot of roughly 10 to 15 mm, customizable, sitting on the deck where the hook will land. Because the trolley carries the hook, the spot moves with it as the operator slews and traverses, and it stays visible against surfaces that daylight would have washed out. The mark is not a broad flood of light; it is a sharp point that the crew can aim at.

Two people can watch the same spot. The operator sees it from the cab, the signalman sees it from the deck, and both are looking at the same point at the same time. A dual-button wireless remote lets either the operator or the ground signalman switch the beam on and off, so the mark can be shown when it is needed and hidden when it is not. On a night shift, with the deck dark and the crew working from artificial light, a single steady green point is often the easiest thing on the whole site to see.

▌  SELF-ILLUMINATED MARK  The green spot is its own light source, so it stays clear when the daylight references are gone.

▌  A SHARP POINT AT NIGHT  A 532 nm spot of about 10 to 15 mm, customizable, gives a precise target rather than a wash of light.

▌  ONE POINT, TWO VIEWS  Operator and signalman watch the same mark, so the landing point is shared rather than imagined.

03  USING THE MARK AS AN EXCLUSION ZONE REFERENCE

The green spot does a second job after dark. During the day, the area beneath a working crane is usually marked out with cones, tape or barriers, and everyone can see where the exclusion zone begins and ends. At night those markers are much harder to read, and the boundary that was obvious at noon can blur into a dark deck. The beam gives the crew a moving reference that sits directly under the trolley, which is exactly where the load will come down and where nobody should stand.

That does not turn the laser into a barrier, and it is important not to treat it as one. The spot marks a point, not an area, and a single point does not enclose a zone. What it does is reinforce the exclusion zone already set by the lift plan: when the green mark is on the deck, it is a clear reminder that the space below the load is working space rather than standing space. Physical barriers, cones and the signalman's control of the area remain the real protection, and the beam is a visible reminder of where that protection applies.

▌  A MOVING REFERENCE  The spot sits directly under the trolley, which is where the load will land and where no one should stand.

▌  REINFORCES THE ZONE  The mark reminds the crew where the exclusion zone is while the physical barriers keep doing the real work.

▌  NOT A BARRIER  One point does not enclose an area; the mark backs up the lift plan, it does not replace the barriers.

▌  EASIER TO READ THAN TAPE  On a dark deck a lit mark is easier to see than cones or tape that disappear into shadow.

04  SETTING IT UP FOR NIGHT SHIFTS

Setting the system up for a night shift is much like setting it up for a day shift, with the checks mattering a little more. The unit is plug-and-play: a 12 V one-to-two connector, lights on power-up, no commissioning needed. The head has a metal housing and waterproof connectors, and it is rated to operate between minus 10 and plus 40 degrees Celsius, so a cold night on site stays within its design range. At the start of the shift the crew powers the unit and confirms that the spot is clean and centred on the deck.

Power deserves the same attention. The ZNAQ-JG1 runs from a 12 V lithium battery and can be supplied in two ways: the charging-pile type, with a trolley charging pile, a long cable and a 12 V ternary lithium pack whose capacity can be customized; or the solar type, with a 20 W solar panel, customizable in output, and a storage control box holding a built-in 10 Ah battery. The manufacturer's care note is to avoid prolonged daytime use to extend service life, which suits a night shift well, because the beam is used when it is genuinely needed. Either way the routine is the same: check the beam before the first lift, and use the remote to switch it on for the lifts that need a landing-point mark.

▌  PLUG-AND-PLAY START-UP  A 12 V one-to-two connector lights the head on power-up, with no commissioning to carry out.

▌  POWER THAT SUITS NIGHT WORK  Charging-pile or solar power keeps the 12 V lithium battery ready, and night use fits the care note about daytime hours.

▌  CHECK BEFORE THE FIRST LIFT  Confirm the spot is clean and centred at the start of the shift, and treat a dim or missing mark as a stop.

05  WHERE IT STOPS AT NIGHT

It is worth being clear about the limits, because night work rewards honesty about equipment. The beam marks a landing point; it does not measure the load, it does not warn of overload, and it does not stop two cranes from conflicting. It does not light the deck for the riggers, and it does not replace the floodlights a night operation needs in order to work at all. Its contribution is narrow and reliable: one visible point under the trolley that the operator and the signalman can both see when the light is poor.

The beam can also fail quietly, and at night a failure may be harder to notice against a busy artificial background. A dirty lens, a flat battery or a loose connector dims or kills the spot, and if the crew does not look for it, they may keep working from a mark that is no longer there. That is why the start-of-shift check matters. The laser is an aid to the operator's eye and to the crew's shared reference, and an aid that is checked is worth having; an aid that is simply assumed is a liability.

▌  NOT A SAFETY DEVICE  The beam does not weigh the load or warn of overload; those duties stay with the monitoring system and the plan.

▌  NOT SITE LIGHTING  The spot marks a point; it does not light the deck for riggers or replace the floodlights a night shift needs.

▌  CHECK IT IN THE DARK  A dim or missing spot is easy to miss at night, so the crew has to look for it before the first lift.

PROCUREMENT IMPACT

●  If the crane works night shifts, a self-illuminated landing mark is one of the simplest references to add to a dark deck.

●  Decide the power option early: the charging-pile type with a 12 V ternary lithium pack, or the solar type with a 20 W panel and a 10 Ah control box.

●  Confirm where the beam will sit relative to the existing exclusion zone, so the mark reinforces the plan instead of competing with it.

●  Check the rated range against the site, since minus 10 to plus 40 degrees Celsius is the operating window on a cold or hot night.

●  Treat the system as a support to the lift plan and a backup to the signalman, and set that expectation with the crew before the first night shift.

WHAT TO WATCH

●  Watch the contrast. A green spot that is obvious on dark concrete can be lost against a lit, reflective surface.

●  Watch the daily check. A mark that is never confirmed at power-up may be trusted long after it has failed.

●  Watch the power. A night-heavy pattern of use should be reflected in how the pack or the panel is specified.

●  Watch the zone. A visible mark is a reminder of the exclusion zone, never a licence to stand closer.

●  Watch the daytime guidance. Running the beam all day for convenience is the quickest way to shorten its 5000-hour life.

ABOUT  ZN Industrial (Shandong Zhinuo) designs and manufactures crane safety monitoring systems, positioning systems and mechanical auxiliary handling equipment for overseas construction, industrial and steel markets.

Standards and regulations vary by market — local rules still govern your site.

▌  CONTACT  shandongzhinuo@outlook.com  +86 176 6371 0314 · en.znaqkj.com

SOURCES · BS 7121 · LOLER 1998 · ASME B30.3 · ISO 12480-1