What Is a Green Beam Multi-Line (4D) Laser Used For?

A green beam multi-line laser — often sold as a "4D" laser — projects several 360-degree planes of green light at once: typically one horizontal plane and two or three vertical planes crossing at right angles. Instead of a single line on one wall, you get level and plumb references wrapped around the entire room in one setup. For fit-out trades, that changes how fast a room gets marked out.

What "4D" actually means

The "D" labels count the 360-degree planes. A 2D cross-line laser gives you one horizontal and one vertical plane. A 4D unit like the Grettz G4D adds further vertical planes, so you get full-room horizontal coverage plus plumb lines on every wall — 16 lines in total once each plane wraps the room. It's a marketing shorthand rather than a formal standard, but the practical difference is real: fewer repositions, and square corners projected for you where the vertical planes cross.

Why green beam?

The human eye is far more sensitive to green light than red, so a green line reads as noticeably brighter on the same power. Indoors under site lighting — or in a bright kitchen extension full of glass — that's the difference between a line you can work to and one you're squinting at. The trade-off is battery draw, which is why most green multi-line lasers, the G4D included, run on rechargeable lithium packs with USB-C charging. For the fuller comparison, see our guide on red beam vs green beam lasers.

The jobs a 4D laser is built for

• Kitchen fitting — one setup gives a level line around all four walls for base and wall units, plus plumb lines for tall units and end panels.
• Tiling — a horizontal datum right round the room and vertical lines for setting out cuts; the crossing planes square up floor grids without a 3-4-5 triangle.
• Suspended ceilings and MF ceilings — a continuous 360-degree ceiling line means perimeter trim goes up against a live reference on every wall at once.
• Partitioning and dry lining — plumb planes transfer floor-track positions to the ceiling directly, and square corners come off the crossed verticals.
• First and second fix — socket heights, radiator brackets, curtain poles, stair stringers: anything that needs level or plumb marks repeated round a room.

What a 4D laser is not for

Outdoors over distance, a rotary laser with a receiver is still the right tool. A multi-line laser's diode spreads its output across several planes, so range and daylight visibility can't match a dedicated rotary laser — and it has no grade function for setting falls. If your week is groundworks, drainage and slab work rather than fit-out, start with our guide to the best laser level for groundworks and civils instead. Plenty of trades end up carrying both: rotary for outside, multi-line for inside.

Choosing between 2D and 4D

If you mostly need a single level line and the odd plumb mark — shelving, picture rails, one wall of tiles — a compact 2D unit does the job for less money and fits in a pocket of the tool bag. Go 4D when you regularly mark out whole rooms: the time saved not repositioning the laser pays for the upgrade quickly on kitchen and bathroom work. Browse the full line laser range to compare.

Getting the most from one on site

1. Mount it at working height — a wall bracket or elevating tripod beats floor level for most fit-out tasks. The G4D kit includes a tripod and telescopic pole for exactly this.
2. Let it self-level and settle before marking; check the out-of-level alarm hasn't tripped if it's been knocked.
3. Work round the room from one setup rather than chasing the laser from wall to wall.
4. Check accuracy periodically — a quick flip test against a marked point takes a minute, and an annual calibration through Service 72 keeps the certificate current with a 72-hour turnaround.

The bottom line

A green beam multi-line (4D) laser is the indoor fit-out workhorse: level, plumb and square references round a whole room from a single setup, in a beam bright enough to work to under site lighting. If that sounds like your day-to-day, the Grettz G4D green beam multi-line laser — backed by UK support and a 3-year warranty — is the place to start.