What gets marked on lenses
Progressive addition lenses carry semi-visible engravings that the wearer does not notice but an optician can find by holding the lens against a light. The two alignment marks sit on the horizontal line, 34 mm apart, and the optician uses them to redraw the fitting cross and check that the lens has been mounted correctly. The temporal mark usually shows the maker's logo with the addition power below it (for example, 25 for a +2.50 add), and the nasal side commonly carries a design or material code. Freeform single vision lenses may also carry a small brand or design identifier.
Optical glass lenses for cameras, microscopes, projectors and inspection systems are a different case. They are usually marked with a part or lot number, sometimes with an orientation arrow, on the edge or on a flange outside the clear aperture, so the mark never sits in the light path.
Which laser marking machine suits lenses
Spectacle lenses are made from CR-39, polycarbonate, high index thiourethane materials and Trivex. These polymers absorb the 10.6 µm wavelength of a CO₂ laser strongly at the surface, which lets the beam make a very shallow micro-engraving without going deeper into the lens. Lens engravers used in freeform labs are commonly built around a CO₂ source for this reason. A UV laser at 355 nm is the other option and gives very fine marks with a small heat affected zone, which helps where marks must be extremely faint or very small.
A standard fiber laser at 1064 nm is not suitable for laser marking on lenses that are clear, because most of the beam passes straight through. On optical glass, a CO₂ laser does produce a frosted mark, but it does so by creating tiny surface cracks, which is acceptable on a bevel and not on a precision surface. UV is usually preferred for finer marks on glass. In many optical assemblies the cleaner answer is to mark the metal barrel or mount with a fiber laser and leave the glass untouched.
When marking the mount is the better choice
On camera and instrument lenses, any mark on the glass carries some risk to the optical surface. Marking the metal barrel, retaining ring or mount with a fiber laser gives a permanent, readable identification and leaves the glass completely untouched.
Setting up the job
For spectacle lenses, positional accuracy matters more than speed in laser marking on lenses. The lens holder has to locate the lens from its geometry so that the two alignment marks land exactly where the lens design puts them, and many labs feed mark positions from their lab software rather than placing them by hand. Visibility is set by trial: too little energy and the optician cannot find the mark, too much and the wearer sees it. Where the engraving step sits in the lab flow, before or after hard coating and anti-reflection coating, changes the settings, so plan it with your process. Keep lenses free of debris with good fume extraction, and inspect marks against a dark background with side lighting.
What to check before you buy
- Wavelength match. Confirm whether your lens materials respond better to CO₂ or UV by marking CR-39, polycarbonate, Trivex and high index samples from your own stock.
- Faint mark control. Ask how finely power and speed can be adjusted, because semi-visible marks sit in a narrow window between invisible and distracting.
- Position accuracy. Check that the two alignment marks land at 34 mm spacing and on the correct axis across repeated lenses.
- Lab data link. If you run a freeform lab, check how mark positions and add power text will move from your lab software into the marking file.
- Coating sequence. Mark test lenses at the stage of your process where you plan to engrave, then coat or finish them as usual and inspect again.
- Glass or mount. For instrument optics, decide early whether the glass itself needs a mark or whether a fiber mark on the mount is enough.
- Clean handling. Plan extraction and lens handling so engraving residue never settles on finished optical surfaces.
Laser marking on lenses in Tamil Nadu
Chennai has some of India's best known eye hospitals and a large network of optical retailers, and Madurai is widely known across the country for eye care. Lens processing labs that supply optical shops in Chennai, Coimbatore, Madurai and Trichy are the natural users of laser marking on lenses, especially as more of them surface freeform lenses locally. Optics workshops that assemble instruments in Chennai's industrial estates have a separate need, usually for edge or mount marking.
NMB Enterprises is based at Poonamallee, Chennai. Lens labs and optics makers anywhere in Tamil Nadu can call or WhatsApp 098417 60722 with the lens materials, photos of an existing marked lens if you have one, the marks you need and your daily volume, and NMB will suggest a CO₂ or UV configuration.