FAQ knowlogue about indoor lighting

PJ‑LED Indoor Lighting FAQ

Product coverage: Panel lights, linear batten lights, LED tubes. Suitable for commercial indoor projects: offices, schools, hospitals, retail shops, underground parking lots.

1. Panel Light (Edge‑lit vs Back‑lit)

Question: What is the difference between edge‑lit panel and back‑lit panel? What are their advantages, disadvantages and recommended applications?Answer: Edge‑lit panel: LEDs are placed along the frame edge. Light travels through a light guide plate for uniform output. It is ultra‑slim and aesthetic. Drawbacks include potential yellowing of the light guide plate, slightly lower efficacy at higher wattage and higher cost. It is ideal for premium offices, showrooms and hotels. Back‑lit panel: LEDs are mounted directly behind the diffuser with no light guide plate. It delivers better thermal performance, higher luminous efficacy, lower risk of dark spots and lower cost, while the fixture body is thicker. It suits standard offices, schools, hospitals and large‑scale retrofit projects.

2. Diffuser Materials: PS, PMMA & PC

Question: What are the differences among PS, PMMA and PC diffusers? Will they turn yellow after long‑time operation?Answer: PS diffuser is low‑cost with decent transmittance, but has poor heat resistance and tends to yellow after years of lighting operation. PMMA offers the highest light transmittance with moderate hardness. PC provides the best anti‑aging and heat resistance with minimal yellowing. It is the preferred choice for long‑lifespan commercial projects though the price is higher. Many low‑cost panels use PS sheets, which will turn yellow and dim within 2‑3 years. PC diffuser is recommended for engineering orders.

3. UGR Control for Office Panel Lights

Question: How to achieve good UGR performance for panel lights? What does UGR＜16 mean and how much efficacy will be sacrificed?Answer: Anti‑glare performance of panel lights is realized by micro‑structured diffuser, larger cut‑off angle or internal louver film. Standard panels normally reach UGR 19~22. To meet UGR＜16 requirement for premium offices, around 7–12% luminous efficacy is sacrificed. According to EN12464, UGR ≤19 is required for general office workstations, while UGR＜16 is specified for high‑end open offices.

4. Mounting Methods: Recessed / Surface‑mounted / Suspended

Question: Panel lights can be recessed, surface‑mounted or suspended. Do these installation ways affect heat dissipation and service life?Answer: Recessed mounting: The fixture is enclosed inside the ceiling cavity. It has the poorest heat dissipation and higher working temperature, so thermal margin must be reserved during selection. Surface‑mounted: The housing is exposed to ambient air for better cooling. Suspended mounting offers the best air circulation and thermal performance. For bulk recessed installation, avoid running fixtures at full power to prevent accelerated lumen depreciation.

5. Dark Spots & Uneven Brightness on Panels

Question: What usually causes dark spots or uneven brightness on panel lights?Answer: For edge‑lit panels, common causes are damaged dot patterns on the light guide plate, aging light guide plate or overheated edge LEDs. For back‑lit panels, dark areas may result from excessive spacing between LED chips, failed individual LEDs or localized thermal decay. Thermally deformed diffuser can also lead to this issue. Quality panels pass uniformity tests. Uniformity ≥0.7 is a widely adopted threshold for commercial projects.

6. Linear Batten vs LED Tube

Question: What is the core difference between integrated linear batten lights and LED tubes? Which one should clients choose for renovation projects?Answer: LED tube is a retrofit solution for existing fluorescent troffers. It reuses the old housing and ballast (ballast‑bypass version is also available). It features low renovation cost, but thermal and optical performance are limited by the original fixture. Integrated linear batten is an all‑in‑one luminaire with housing, driver, LEDs and optics fully optimized together. It provides better heat dissipation, light uniformity and glare control. It can be directly suspended or surface‑mounted. It is recommended for new construction or full fixture replacement retrofits for longer service life and better consistency.

7. Daisy‑chaining of Linear Lights

Question: Can linear lights be connected endlessly? What is the maximum quantity per circuit? Will long‑distance daisy‑chaining cause voltage drop and uneven brightness?Answer: Unlimited daisy‑chaining is not allowed. The maximum number per circuit is determined by driver output power and cable gauge. Voltage drop exists along the chain. Too many fixtures on one run will make the units at the far end dimmer. We specify the maximum connected quantity for each circuit. Split feed is suggested for long runs.

8. SDCM Requirement for Retail Linear Lighting

Question: Why do retail chain projects require SDCM ≤3 for linear lights?Answer: Retail chains install dozens of linear lights continuously along aisles. SDCM 5 may show visible colour difference between fixtures from a distance. SDCM ≤3 guarantees uniform colour appearance across the whole lighting run with no noticeable mismatch. However, stricter LED bin sorting increases material cost.

9. 0‑10V / DALI Dimming for Linear Lights

Question: What is the key to flicker‑free dimming for linear lights with 0‑10V or DALI control? What is the minimum dimming level?Answer: Flicker‑free performance heavily depends on driver quality. Premium constant‑current drivers maintain low flicker from 10% to 100% output. Budget drivers often produce flicker below 20% brightness. For schools, offices and filming rooms, confirm SVM＜1 across the whole dimming range.

10. LED Tube Wiring Types

Question: There are ballast‑compatible, ballast‑bypass, single‑end power and double‑end power LED tubes. How to choose?Answer: Ballast‑compatible tubes can be plugged directly into existing fixtures without rewiring for fastest installation. But tube lifespan depends on the old ballast, and a faulty ballast will cause premature failure. Some North‑American projects restrict this type. Ballast‑bypass (direct wire): Remove the original ballast and connect mains voltage directly. It provides the best long‑term reliability and is widely recommended for retrofits, though electrician rewiring is required. Single‑end power: Mains supply connects only to one pin for higher safety. Double‑end power: Live voltage exists at both ends, common for legacy fluorescent fixtures. Many overseas projects specify bypass‑type tubes only.

11. Energy Saving Calculation for LED Tube Retrofit

Question: LED tube replacement claims 50% energy saving. How is this calculated? What losses should be considered?Answer: A traditional 36W T8 fluorescent lamp consumes roughly 40W total power including ballast loss. An 18W LED tube draws about 18W. Energy saving rate = (40‑18)/40 = 55%. Energy saving is calculated based on total system power instead of lamp wattage only. Old magnetic or electronic ballasts consume extra standby power, which is why the bypass solution achieves higher savings.

12. Low‑temperature Performance of LED Tubes

Question: Will low‑temperature environments such as cold storage or underground garages affect LED tube startup?Answer: Standard LED tubes operate within 0~40℃. Below 0℃, electrolytic capacitors inside the driver degrade, resulting in slower startup and slightly reduced lumen output. Cold storage projects require special low‑temperature drivers rated ‑20℃~+45℃, which need to be custom ordered in advance.

13. IP Rating for Indoor Luminaires

Question: What does IP40 mean for indoor lights? Is it necessary to upgrade to IP44 for restrooms and corridors?Answer: IP40: Protected against solid objects ≥1mm, no water protection. IP40 is sufficient for dry offices, classrooms, corridors and retail spaces. IP44 offers protection against splashing water. It is only required for humid zones such as restrooms and pantries. IP65 is generally unnecessary for indoor commercial lighting and brings extra cost.

14. PF & THD Requirements for Commercial Indoor Lighting

Question: Many school and hospital projects specify PF＞0.9 and THD＜20%. Why?Answer: PF＞0.9 ensures high utilization of active power. High THD generated by a large number of parallel luminaires may interfere with hospital medical instruments, school electronic equipment and cause cable overheating. Some low‑cost drivers can reach PF>0.9 but with poor THD performance. EU ERP rules and many public tenders set THD limits.

15. Flicker & SVM Index

Question: What scenes require flicker‑free lighting with low SVM?Answer: SVM＜1 is the common threshold for flicker‑free lighting. Low flicker performance is mandatory for classrooms, offices, hospitals, video conference rooms and live streaming studios. Flicker may lead to eye strain and headache. The requirement can be relaxed for storage corridors.

16. Maintenance Factor for Dialux Simulation

Question: What MF (maintenance factor) values should we use for indoor commercial lighting Dialux calculation?Answer: MF = 0.8 for clean offices and hospitals; MF = 0.7 for retail shops; MF = 0.6 for dusty underground car parks and storage rooms. The maintenance factor accounts for lumen loss caused by dust accumulation and fixture aging. Using a fixed MF=0.8 for all spaces may result in insufficient illuminance after several years of operation.

17. Certification Requirements by Market

Question: CE, UKCA, DLC and UL. What are the certification priorities for these indoor lights in different markets?Answer: EU market: CE + ERP; UK market: UKCA; North America: UL/ETL, DLC is needed for utility rebate projects; Australia: SAA. Important note: Certificates are issued for the complete luminaire. Changing drivers or LED bins will invalidate the certification. Many LED tube suppliers only hold UL Recognized certification for separate drivers, instead of full UL Listed for finished tubes.

18. 5‑Year Warranty Exclusions

Question: What damages are excluded from the 5‑year warranty for indoor luminaires?Answer: Exclusions include incorrect wiring, sustained overvoltage, site lightning surge, mechanical damage during installation, operation beyond specified temperature or humidity range, poor heat dissipation caused by heavy dust buildup without regular cleaning. Slow natural lumen depreciation is not covered by warranty.

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