A teardrop light is a cleanroom-specific pendant luminaire with a teardrop-shaped cross-section. It clamps beneath the ceiling T-bar grid, between two HEPA filters or FFUs. It exists for one reason only: in a unidirectional-flow cleanroom the ceiling is fully covered with filters, so a recessed flat-panel light has nowhere to go, while any light hanging in the airflow must not disturb the laminar flow. This article uses an airflow diagram to explain what the teardrop shape does, compares the four construction types on the market, and shows how to work out illuminance and the number of fixtures.
The cleanroom ceiling dilemma: once filters cover everything, where do the lights go?
In an ISO 4–6 (Class 10–1000) unidirectional-flow cleanroom, almost every grid cell in the ceiling is the outlet face of an FFU or a HEPA filter, with air moving straight down at 100–200 fpm (roughly 0.5–1.0 m/s). An office-style flat panel recessed into the ceiling pays two penalties here:
- ▸One less filter cell: the light takes a grid cell, that cell no longer delivers filtered air, and the filter coverage ratio of the ceiling drops.
- ▸One more seal: GB 50073-2013 (Code for design of clean room) §9.2.2 states that general lighting fixtures in cleanrooms should be surface-mounted on the ceiling; when they are recessed into the ceiling, the installation gap must be reliably sealed and cleanroom-specific fixtures must be used. Every recessed light is another opening cut into the ceiling.
The 1994 US patent US 5,313,375 spells out the solution: shape the light as a teardrop, suspend it from the T-bar framework of a standard ceiling grid between the HEPA filters, and let the smooth sides pass the laminar flow on either side without disturbing it. That is the teardrop light.
Flat panel vs teardrop under unidirectional flow
Left: a recessed panel takes a filter cell and drags eddies under its flat base; right: a teardrop hangs below the grid and lets the flow slide past and rejoin
What a teardrop light is: shape, mounting and its limits
Cut through a teardrop light and the cross-section shows a narrow top face about 50 mm wide that sits right under a 2-inch T-bar; below it the body widens first, then closes into a round arc. Air leaving the filters on both sides hugs the housing as it passes and rejoins quickly beneath the fixture, instead of dragging a mass of eddies underneath the way a flat-bottomed panel does. There is no flat top surface for dust to settle on, and the sides are one continuous curve with no blind corners when wiping.
There are two ways to mount it: bolted to the grid with T-bolts, either as a single fixture or end-to-end in a continuous row; or, on a ceiling without a grid, fixed to the ceiling face with self-tapping screws.
The same patent is candid about the limitation: this mounting method usually allows only one row of tubes every 4 feet, so light output is limited. Selecting teardrop lights is therefore not just a matter of "how many to buy"; illuminance has to be calculated first, and we run the numbers below.
4 teardrop light constructions on the market, compared
Teardrop lights all look much alike; the differences lie in how the body is built, whether the light source can be replaced, and how fixtures are linked together. The market falls broadly into four types:
| Type | Body material | Light source | When a tube fails | Linking and wiring | Characteristics and trade-offs |
|---|---|---|---|---|---|
| A Powder-coated steel + tubes | Cold-rolled steel sheet with white powder coating; some brands offer aluminium or stainless steel | T8/T5 fluorescent or LED tubes | Replace the tube | Mostly wired fixture by fixture | Cheap, longest track record; the coating chalks and sheds flakes after a few years, right below the air outlet |
| B Integrated LED (European/US brands) | Streamlined aluminium housing | Built-in LED module, 2,250–8,000 lm per fixture | Cannot replace just a tube; the whole fixture is replaced | Quick connectors for continuous rows | High lumen output per fixture, DALI dimming available; protection is often only IP40, operating temperature 0–35 °C |
| C Extruded PC integrated LED (mainland China) | Extruded PC housing, about 1200×45×84 mm | Built-in LED, rated L80 about 54,000 h | Whole fixture replaced | Plug-in quick connectors | High protection at IP65 and IK05; the PC housing is sensitive to sulphides and some cleaning agents |
| D Extruded aluminium body + replaceable Philips T8 LED tube | Extruded aluminium alloy channel + PC+GF wire cover | Philips MASTER LEDtube 13 W / 2100 lm / 50,000 h, swappable for 4000 K or yellow-light tubes | Twist out the tube and fit a new one; the fixture stays in place | 3-pin quick connector built into the fixture, trunk wire up to 2.4 mm | No paint flakes, low relamping cost, 100–240 V; lumen output per tube is lower than integrated types, so the count must be calculated |
The specifications for A–C in the table are taken from the public datasheets of representative products of each type; they describe "the common practice for that type", not guaranteed values for any specific model. D is the specification of the cleanroom teardrop LED light.
None of the four types is absolutely better or worse; three things make the real difference.
1. The body ten years on: does it shed particles?
In a cleanroom, the enemy of powder coating is not scratching but ageing. After a few years the coating chalks and sheds fine flakes, and the teardrop light hangs directly below the air outlet and directly above the work surface. Extruded aluminium has no paint layer to peel; the trade-off is that a scratch shows immediately. But the fixture hangs where people cannot reach, so the chance of scratching is low, whereas particle shedding happens every single day.
2. When it fails: replace a tube, or the whole fixture?
Integrated LED fixtures deliver high lumen output per unit, but when the LED module or driver fails the entire fixture must be replaced and the quick connectors reconnected. The replaceable-tube approach turns the shortest-lived component into a consumable: the Philips MASTER LEDtube is rated for 50,000 h (70% lumen maintenance) and 200,000 switching cycles, and when it fails you climb a ladder, twist it out and fit a new one, with no changes to the fixture or the wiring. For a cleanroom, one less fixture removal is one less contractor entry.
3. Linking: how thick a wire can the quick connector take?
A row of teardrop lights is linked with quick connectors, saving the stripping and crimping of every single fixture. The difference lies in the wire gauge the connector accepts: with a connector that takes up to 2.4 mm, the trunk line can use 2.0 mm wire without dropping to 1.6 mm, the circuit can be rated at 16–20 A, and more fixtures can be chained on one circuit; with a connector limited to 2.0 mm or less, the circuits have to be split finer.
No cover vs removable PC cover: Class 1000 is the dividing line
| Item | No cover | With removable PC cover |
|---|---|---|
| Light source position | Frosted-glass T8 tube exposed inside the reflector | Tube enclosed in the PC cover |
| Relamping | Twist out the tube | Remove the PC cover first, then change the tube; the cover can be refitted repeatedly |
| Light | Direct, high efficiency | Softened by the PC cover, less glare |
| Cleaning | Wipe the housing and the tube | Continuous outer surface, can be wet-wiped |
| Suitable for | ISO 7–8 (Class 10,000 and above) general electronics and optoelectronics clean areas | Class 1000 (ISO 6) and stricter grades, GMP areas that need regular wet-wiping or spray disinfection, and places at risk of impact |
The rule is simple: at a cleanliness grade of Class 1000 (ISO 6) or stricter, add the cover, so that the tube, lamp holders and contacts are all enclosed and no fragments can fall into the clean zone if a tube breaks. Note that plastic parts such as the PC cover and lamp holders are affected by sulphides, petroleum-based solvents and certain cleaning agents, so tell the supplier which cleaning agents are used on site when selecting.
How much illuminance, and how many teardrop lights
| Source | Area | General lighting illuminance |
|---|---|---|
| GB 50073-2013 §9.2.3 | Production rooms in cleanrooms without daylight windows | 200–500 lx |
| GB 50073-2013 §9.2.3 | Auxiliary rooms, personnel and material cleaning rooms, air locks, corridors | 150–300 lx |
| GB 50472-2008 §12.2.1 | Main production rooms in electronics-industry cleanrooms | 300–500 lx |
| GB 50472-2008 §12.2.1 | Auxiliary work rooms, cleaning rooms, air locks and corridors in electronics plants | 200–300 lx |
GB 50073-2013 §9.2.4 further requires a general lighting uniformity of no less than 0.7. Process areas in semiconductor and display fabs are often specified higher; cleanroom design data from Japanese lighting manufacturers commonly targets about 1,000–2,000 lx on the work surface.
The fixture count is roughly estimated with the lumen method: Number of fixtures = target illuminance × area ÷ (lumens per fixture × utilisation factor × maintenance factor). Using 2100 lm per tube, a utilisation factor of 0.6 (white interior, fixtures mounted low) and a maintenance factor of 0.8:
| Target illuminance | Four-foot single-tube fixtures per 100 m² | Average area covered per fixture |
|---|---|---|
| 300 lx | 30 fixtures | about 3.3 m² |
| 500 lx | 50 fixtures | about 2 m² |
| 750 lx | 75 fixtures | about 1.3 m² |
| 1,000 lx | 100 fixtures | about 1 m² |
When every 1200 mm grid bar carries a continuous row of single-tube fixtures, each fixture covers about 1.44 m², which works out to roughly 700 lx as the ceiling for single tubes; for higher targets you need the twin-tube version, or lights on the 600 mm cross bars as well. These figures are only a first estimate; the final layout should be run in lighting software using the floor plan and the ceiling grid drawing.
Yellow-light areas: 6500 K white cannot be used as is
The photolithography area must block the short wavelengths that would expose the photoresist; resist manufacturers typically require everything below 500 nm to be filtered out. A 6500 K white LED has a strong blue peak around 450 nm and cannot simply be installed in a yellow-light area. Here the replaceable-tube teardrop light has a practical advantage: the fixture body stays the same, and you fit LED yellow-light tubes or slide an amber filter sleeve over the tube. When choosing yellow-light tubes, ask the manufacturer for a spectrum plotted on a logarithmic scale, because many products still have side lobes at 420–450 nm that do not show up on an ordinary linear spectrum plot.
7 questions to ask the supplier before buying
- 1Is the body extruded aluminium, powder-coated steel or extruded PC? For coated parts, ask how particle shedding from the aged coating is dealt with.
- 2Can the light source be replaced on its own? What are the tube model, rated life (how many hours to L70) and switching cycles?
- 3What is the maximum wire gauge the quick connector accepts? How many fixtures can be chained on one 16–20 A circuit?
- 4Is the cover removable or sealed in one piece? Is there a covered version for areas of Class 1000 and stricter?
- 5Do the protection rating (IP) and operating temperature range cover the site's cleaning methods and ambient temperature?
- 6How compatible are the PC cover and lamp holders with the cleaning agents and disinfectants used on site?
- 7Can the supplier provide illuminance calculations and a layout drawing from the floor plan and grid drawing?
Line up the 7 answers side by side and the differences between the four types become obvious. For the selection logic of other cleanroom peripheral equipment, see the cleanroom equipment series and the FFU selection guide.
FAQ
Q: How does a teardrop light differ from an ordinary LED flat panel?
In position and shape. A flat panel is recessed into the ceiling, takes up a filter cell and adds an opening that must be sealed; a teardrop light hangs below the grid, between the filters, and its teardrop cross-section lets the laminar flow slide along the housing. GB 50073-2013 §9.2.2 requires cleanroom fixtures to be surface-mounted, with reliably sealed gaps if recessed; a teardrop light is surface-mounted by nature.
Q: Do ISO 7 and ISO 8 cleanrooms need teardrop lights too?
Not necessarily. ISO 7–8 ceilings are mostly ducted with terminal HEPA diffusers, leaving empty cells where recessed cleanroom fixtures can go, which is fine as long as the gaps are sealed properly. The home ground of the teardrop light is the ISO 4–6 unidirectional-flow area with full FFU coverage and no empty ceiling cells.
Q: Is a single 13 W, 2100 lm teardrop light bright enough?
Do not think of it as a one-for-one swap. It gives about a third less light than a 36 W T8 fluorescent tube at roughly 3070 lm; what it saves is power (13 W versus 36 W) and relamping (about 3 times the life). Work out the count with the lumen method: a 60 m² room at 500 lx needs about 30 four-foot single-tube fixtures, assuming a utilisation factor of 0.6 and a maintenance factor of 0.8.
Q: If the extruded aluminium body gets scratched, does that affect cleanliness?
A scratch shows more on extruded aluminium than on a coated part, but the scratch itself does not shed particles; only the appearance is affected. Coated parts are the opposite: scratches are less visible, yet the coating keeps shedding flakes as it ages. Cleanroom fixtures hang out of people's reach, so the chance of a scratch is far lower than the chance of coating degradation.
Q: An integrated LED teardrop light is rated L80 at about 54,000 hours. Is it more durable than the replaceable-tube type?
The numbers cannot be compared directly. L80 is the time until lumen output falls to 80%, while the Philips tube's 50,000 h is a rated life at 70% lumen maintenance; the two are defined differently, and the B value (failure fraction) that follows is often different too. The real difference comes after a failure: the integrated type needs the whole fixture replaced and reconnected, while the replaceable-tube type needs only one tube.