Read the sheet in the order it is installed
Nothing on a spec sheet is dishonest; plenty of it is irrelevant. A glass gobo engraving process sheet will quote lumen output, power draw and beam angle, but what you need is image width at your throw distance and contrast against the light already on the surface. Those require two more numbers the sheet usually does not give you, which is why they are worth asking for.
Output numbers, ranked by how much they lie
Three output figures get mixed up constantly: lumens describe what the lamp produces, lux describes what arrives on the surface, and watts describe what you pay for. A glass gobo engraving process drawing 30–200 W might deliver 3,000 lumens, but the lux at the wall depends entirely on how wide you spread it. The same lamp projecting a 1 m image is nine times brighter than the same lamp projecting a 3 m image.
The two numbers that must be quoted together
Check whether the quoted throw is to a white wall in a dark room, because that is where the number comes from. On a glass gobo engraving process intended for a retail window, the realistic working distance is usually shorter than the maximum on the sheet, since contrast — not reach — is what fails first.
The optical spec most sheets leave out
Gobo size is quoted as an outer diameter, but what matters is the image area — the part the light actually passes through. A 53 mm gobo may only have a 45 mm image circle, and artwork sized to the outer diameter gets cropped. For a glass gobo engraving process, ask for both figures before you commission artwork, because a file drawn for the wrong one is wasted.
The compliance block
Ratings age. A glass gobo engraving process that left the factory rated IP65 can lose that rating the first time somebody opens it to change a gobo and reseats the gasket badly. Look for a design where routine access does not mean breaking the environmental seal, or accept that the rating applies to the unit as delivered, not as maintained.
