The starting point
Read illuminance together with distance, beam or field angle, colour and the optical setting used for the test. Compare coverage as well as the centre reading. A high lux figure without these conditions cannot establish how a fixture will light your stage.
Keep the conditions beside the number
An illuminance value describes light reaching a surface. To interpret it for a purchase, you need the measurement distance and the fixture’s operating state. White output, a saturated colour, a narrow zoom and a wide zoom are different conditions. Do not place their readings in one comparison column as though the tests were equivalent.
Ask whether the figure is a centre reading or part of a measured distribution across the beam. Record the units and whether the distance is measured from a defined optical reference. If a quotation only repeats a promotional output number, request the corresponding photometric sheet and the exact model or variant to which it applies.
Estimate the footprint before comparing brightness
For a simple symmetrical cone, an approximate footprint diameter on a perpendicular flat surface is 2 × distance × tan(angle ÷ 2). As a geometric example, a 10° full angle at 10 metres gives a diameter of about 1.75 metres. This is an illustration of geometry, not a claim about a YL fixture’s measured beam or uniformity.
Real fixtures and real targets need more information. Beam and field angles use different intensity boundaries; ask which definition the supplied figure uses. An angled stage surface, a non-circular wash and a zoom mechanism can change how useful the simple estimate is. Use the estimate to ask better questions, then check the actual photometry and a demonstration.
Read the distribution, colour and optics
A bright centre does not tell you whether the edges are usable or how two fixtures will overlap. For illumination work, examine the area you need to cover and the variation across it. For a projection task, also look at focus, image quality and the effect of gobos or framing on useful light.
Keep the colour setting attached to the reading. White-light output does not establish output in every mixed colour, and a photograph’s exposure can make two fixtures appear more similar or more different than they are. When camera reproduction matters, output and colour behaviour should be assessed as separate parts of the test.
Use a comparison sheet with matched columns
If the suppliers provide different test conditions, leave those differences visible. A comparable demonstration at your intended distance can be more useful than forcing unlike numbers into a ranking. Your comparison should identify unanswered questions, not hide them behind a single score.
- Exact model, variant and light-source configuration.
- Distance, beam or field-angle definition, and zoom setting.
- Colour and any optical effects active during measurement.
- Illuminance values and distribution across the target area.
- Measurement method, source document and test date where supplied.
- The stage area and level of overlap the proposed quantity must cover.
Send a drawing with the output request
A useful YL enquiry includes the mounting height, throw distance, target width, intended colours and whether you are lighting people, scenery or aerial effects. Include your shortlisted models and fixture quantities. Ask for the current photometric information at relevant settings, then use the same brief when assessing a sample. This connects the specification sheet to the actual result your project needs.
Common questions
Can I choose a fixture using wattage alone?
No. The source, optical efficiency, beam angle, colour and working distance all affect useful illumination. Keep those conditions attached to the output information.
Is the geometric footprint a guarantee of even coverage?
No. It only estimates a cone’s size. Real intensity distribution, angle definitions, optical settings and the target surface need to be checked separately.
Ready to apply this to your project? Share the model shortlist and the details you have gathered.
