Start from the wall and work backwards
Most color filter brightness loss sheets list ten numbers and leave out the three that decide the result. Work from the wall backwards — image size, throw distance, ambient light — and treat everything else as supporting detail. The numbers that matter are the ones you can verify on site with a tape measure and a lux meter.
Lumens, watts and what reaches the wall
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 color filter brightness loss in the 50–300 W class, ask instead for measured image lux at a stated distance — a supplier who has that number has actually tested the unit.
The two numbers that must be quoted together
The useful specification is the throw ratio, or failing that a distance-to-image-width table. On a typical color filter brightness loss covering 6–35 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 6 m | 0.5 – 1.5 m | Bright and easy — most indoor work |
| Mid, around 35 m | 1.5 – 3 m | Where lens quality starts to matter |
| Long, beyond 35 m | 3 m and up | Contrast fails before reach does |
The optical spec most sheets leave out
Two numbers govern the image: gobo image area and the resolution the lens can carry. Glass gobos can be engraved far finer than any color filter brightness loss 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.
What a good supplier answers without hesitating
Four questions separate a supplier who knows the product from one reading a sheet. What is the image width at my throw distance? What is the gobo image area? Is the IP65 rating for the housing alone or the whole assembly? And what is the lead time on a replacement gobo? A good supplier answers all four in one reply.
