Equivalent Luminaires: Technical Comparison, Calculation and Approval Steps

When another product is proposed in place of a luminaire on the bill of quantities, wattage is often the first value people check. Yet two luminaires of the same wattage can produce different amounts and distributions of light, may not fit the ceiling, or may not work with the project's control system. An equivalence review puts these differences into numbers before the order is placed.

What does equivalent luminaire mean?

An equivalent luminaire does not have to look like the reference product; it has to deliver the result the specification requires under the same conditions. Documents may say "or equivalent", "or equal" or "equal and approved", and a formal request to change the product is often called a substitution request.

When does an equivalent come up?

• When the reference product's lead time does not fit the programme.
• When an alternative is needed for budget reasons.
• When the reference product is discontinued or unavailable.
• On jobs where the specification is open to more than one manufacturer.

Which values are compared?

The acceptable deviation should be stated in the specification. Some specifications, for example, define a range such as ±5% for power and luminous flux. If no range is stated, treat the specified values as minimum or maximum limits.

Why are wattage and lumens not enough?

Take a 96 m² office with a 500 lux target and a maintenance factor of 0.8. Using the lumen method, three options compare as follows:

Equivalent B has more lumens, but it delivers less of its light to the working plane, so it falls short at the same quantity. Equivalent A uses less energy but does not reach 500 lux with 28 luminaires; raising the quantity to 30 also changes the ceiling layout and circuits. These figures are examples; the final result comes from calculation software.

How is an equivalent evaluated, step by step?

1. Define the reference: collect the specified thresholds and the reference product's datasheet.
2. List the values side by side: complete the table above separately for each luminaire type.
3. Repeat the calculation: use the proposed luminaire's LDT or IES file with the reflectance, maintenance factor, working plane and layout values of the original calculation, and check the Ēm, Uo and UGR targets.
4. Check compatibility: cut-out, recess depth, suspension points, driver location and control line must fit the project.
5. Review the documents: the wattage and lumens in the file must match the datasheet.
6. Request a sample: if appearance, colour or glare matters, try the sample in the space.
7. Get written approval: record the approval of the architect, consultant or supervising body per luminaire type.

What should an equivalence submission include?

• A comparison table showing the reference and proposed product values.
• The proposed luminaire's datasheet and LDT or IES file.
• The illuminance calculation repeated with the proposed luminaire.
• CE declaration of conformity and luminaire safety test information.
• Test reports for luminous flux and lifetime (IES LM-79, LM-80, TM-21); see the L70, L80 and B10 guide for what the terms mean.
• Mounting detail, wiring diagram and warranty document.

Equivalents on public tenders and private jobs

In Türkiye, Article 12 of Public Procurement Law No. 4734 states that technical specifications cannot include features or descriptions aimed at a particular brand or model. Where no national or international technical standard exists, or the technical characteristics cannot be defined, a brand or model may be named with the words "or equivalent" ("veya dengi"). On private jobs the rule is set by the contract and specification; where a specification allows only named products, an equivalent depends on the employer's approval.

This section is not legal advice. The tender documents, contract and current legislation apply in each case.

Cases that need a separate look

• Track systems: track, adapter and spotlight must match; magnetic track is usually assessed as a complete system.
• Additions to an existing installation: colour difference and control compatibility come first for products placed next to old luminaires.
• Continuous linear runs: module length, joint detail and total run length must stay the same.
• Emergency lighting: the escape route calculation is redone with the proposed luminaire and emergency kit values.
• Luminaires designed for the project: if the size or form is not standard, custom manufacturing may be the better route.

Common mistakes

• Comparing only wattage or lumens.
• Accepting "the same values" without a photometric file.
• Repeating the calculation with different reflectance or maintenance factors to make the result look better.
• Leaving driver and control compatibility to the site.
• Starting ceiling work without checking the cut-out.
• Getting approval verbally and not recording it per luminaire type.

Conclusion

A good equivalence review compares a quote not only on price but on whether it delivers the same result. Defining these criteria as an equivalence clause in your specification makes the process easier. If your bill of quantities names another brand, the wattage, luminous flux, optics, CRI, IP and control values are compared with our catalogue products and a suitable equivalent is stated in the quotation; if the illuminance target must be documented, the calculation is repeated in DIALux or Relux with the proposed luminaire. For details see luminaire supply for contractors or send us your list.