Read the sheet in the order it is installed
Nothing on a spec sheet is dishonest; plenty of it is irrelevant. A custom glass gobo projector 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
Treat the lumen figure as a rough sorting tool and nothing more. It ignores the lens, the gobo transmission and the colour filter, any of which can take a third of the output. For a custom glass gobo projector in the 30–250 W class, ask instead for measured image lux at a stated distance — a supplier who has that number has actually tested the unit.
Throw distance and image size
The useful specification is the throw ratio, or failing that a distance-to-image-width table. On a typical custom glass gobo projector covering 5–30 m, the zoom lens might take the image from roughly 0.8 m wide at the near end to 3 m at the far end. Once you know the width you need, the throw tells you where the bracket goes — not the other way round.
Gobo size, image area and resolution
The spec most sheets omit is the maximum artwork resolution the optics can resolve. A custom glass gobo projector with a good lens will render fine detail that a cheaper unit turns to mush, which means the limiting factor is often the projector, not the gobo. If your design has thin strokes, ask what line width the system holds at your throw distance.
IP rating and electrical data
IP65 is the number to check for anything outdoors, but read what it covers. The first digit is solid ingress, the second is liquid. IP65 on a custom glass gobo projector means dust-tight and protected against water jets, and it says nothing about the bracket, the gland or the connector, which are the parts that actually fail. Ask whether the rating covers the whole assembly or just the housing.
Questions worth asking the supplier
The most revealing question is about failure. Ask what the most common warranty claim on this custom glass gobo projector is and how it is resolved. A supplier who answers honestly is worth more than one with a slightly better spec sheet.
