Start from the wall and work backwards
Nothing on a spec sheet is dishonest; plenty of it is irrelevant. A heat resistant color filter 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 heat resistant color filter in the 100–400 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 heat resistant color filter covering 8–40 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.
| Throw | Typical image width | Practical note |
|---|---|---|
| Short, around 8 m | 0.5 – 1.5 m | Bright and easy — most indoor work |
| Mid, around 40 m | 1.5 – 3 m | Where lens quality starts to matter |
| Long, beyond 40 m | 3 m and up | Contrast fails before reach does |
Gobo size, image area and resolution
Two numbers govern the image: gobo image area and the resolution the lens can carry. Glass gobos can be engraved far finer than any heat resistant color filter lens in this class will resolve, so the practical limit is optical. That is worth knowing before you pay for engraving detail nobody will see from 10 m away.
IP rating and electrical data
Ratings age. A heat resistant color filter that left the factory rated IP67 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.
