Lamp labels: lumens, watts, colour temperature and a purchase list.
Which lamp-label numbers describe light output and power rather than an electrical design?
Read each label quantity on its own basis
The Department of Energy describes input power in watts, light output in lumens and correlated colour temperature in kelvins. These are different quantities: watts do not directly equal brightness, and a colour-temperature number is not the same as a surface temperature or an electrical installation specification.
Compare products only within an established fixture specification
Record the existing luminaire’s stated compatibility and the selected bulb’s product data. This article does not choose wiring, sockets, circuit protection, outdoor electrical equipment or fixture placement. Resolve compatibility with the manufacturer or an appropriate professional before treating bulbs as alternatives.
Count a supplied lamp schedule
If an already established plan lists three compatible lamps each needing one selected bulb, purchase count is three. With hypothetical two-bulb packs, two packs supply four bulbs. The surplus bulb does not create a new installed lamp position.
Do not infer room illumination from a lumen sum
Three selected lamps each labelled 800 lm have a summed nominal output of 2,400 lm. That sum does not tell you illuminance at a desk or certify sufficient task light, because distribution, distance and room conditions matter. Use the quantity only as a named label total in the purchasing record.
Use the matching calculator
Use this decision sequence
- Record the exact item and the scope described below.
- Check the cited guidance against your product or local growing conditions.
- Measure only the quantities needed for the selected plan.
- Keep the supplied assumptions with the purchase estimate.
Keep the quantities distinct
| Quantity or assumption | How to use it |
|---|---|
| Watts | Power input. |
| Lumens | Nominal light output. |
| Kelvins | Correlated colour-temperature label. |
Worked comparison
Three selected bulbs sold in two-bulb packs require two packs. At a hypothetical 7 per pack, the bulb purchase is 14 before other supplied charges.
Check before using the estimate
No electrical design, fixture installation or illumination compliance is provided.
All dimensions, product properties, prices and specifications in this example are illustrative arithmetic inputs. Use the values from your measured plan, selected product data sheet and supplier quote. This guide does not choose construction specifications or certify safety.
Sources and product references
References support the factual distinctions and scope described above. Growing guidance is regional and care instructions are product-specific. Worked numerical examples are independent illustrative arithmetic.
Calculation and scope checked 2026-10-13. Methods and scope.