What Is the Luna G3?

The Luna G3 is an auto-titrating CPAP (AutoCPAP) machine manufactured by BMC Medical and distributed in the United States primarily by React Health under the Luna brand. The physical device is identical to the BMC G3 A20 sold in international markets. The Luna G3 ships with different firmware versions that write different SD card formats. CPAP Clarity has been verified against contributor data on G3-2.SC.73.04, G3-2.00.77, and G3-2.11.02.33.

BMC Medical is the same company behind the BMC E-20A, the machine commonly supplied through UK rental programs like Intus Healthcare. The Luna G3 sits above the E-20A in the product line. It offers a similar set of therapy features but a more modern internal architecture.

For most users, the Luna G3 does the core job well: it automatically adjusts pressure throughout the night to keep the airway open, logs your therapy data to an SD card, and supports comfortable exhalation relief via Reslex (BMC's equivalent of ResMed's EPR).

The challenge has been reading the data. The Luna G3's SD card format is proprietary and, until now, unsupported by any free web-based tool. CPAP Clarity now reads it directly in your browser. See what CPAP Clarity shows for the Luna G3.

What the Luna G3 Records

Every night, the Luna G3 writes waveform data and event records to its SD card. Here is what CPAP Clarity can decode from that data.

Therapy pressure: The continuous pressure waveform sampled at 50 Hz. You can see exactly how your pressure changed across the night and how the AutoCPAP algorithm responded to events.

Leak rate: The mask seal measurement sampled at 10 Hz, reported in liters per minute. Leak is one of the most actionable metrics in your data: high leak means your mask is not sealing properly, which reduces therapy effectiveness.

Obstructive apneas: Complete breathing pauses caused by airway collapse, with timestamps.

Central apneas: Breathing pauses where the brain does not send the drive signal to breathe, with timestamps.

Hypopneas, unclassified apneas, and RERAs: Partial airflow reductions, events the firmware could not classify, and respiratory-effort-related arousals. All three are decoded from the card's event log, with counts verified night by night against OSCAR's reading of a contributor's card.

Machine settings: The complete settings snapshot from your SD card, including therapy mode, pressure range, Reslex level, humidity setting, ramp time, mask type, and tube type.

Session timeline: Each night's session with start time, end time, and usage duration.

What it does not record

These are firmware-level format boundaries, not limitations of CPAP Clarity.

Per-second respiratory rate: Not present in the waveform files of the legacy G3-2.SC.73 firmware in any identifiable encoding. The newer G3-2.11.x family does not store a rate either, but it writes a per-breath event log, and CPAP Clarity works your respiratory rate out from that.
Per-second tidal volume: The waveform packet layout reserves the positions used for RR/TV/MV in older BMC firmware, but the fields contain zero or non-physiological values.
Per-second minute ventilation: Not recorded.
Flow limitation index: Not surfaced. The card carries per-breath markers that look like flow-limit events, but they are unvalidated, so CPAP Clarity does not chart them.
Snore index: Not recorded.
Cheyne-Stokes respiration (CSR): Not recorded. Only ResMed machines expose CSR detection in CPAP Clarity.

If you are coming from a ResMed AirSense 11 and are accustomed to seeing respiratory rate, tidal volume, and flow limitation curves, expect tidal volume and flow limitation to show "no data" on the Luna G3 dashboard; respiratory rate appears only on the newer G3-2.11.x firmware family, where it is worked out from the breath-by-breath record on the card. The absence of those channels does not mean your therapy is failing. AHI, pressure, and leak are the primary metrics for evaluating treatment effectiveness.

How to Read Your Luna G3 Data

Accessing your Luna G3 data requires only the SD card in the machine and a computer.

Power off the Luna G3. The SD card slot is on the back of the machine at the humidifier end, next to the transfer box that connects the water chamber. Push the card in to release it and remove it.
Insert the card into your computer. If your computer does not have a built-in SD card reader, a USB-C SD card reader costs a few dollars and works with any machine.
Open cpapclarity.com in your browser. No installation, no account, no subscription required.
Drop the whole SD card folder onto the import area. Select the entire SD card contents. Do not navigate into subfolders or select individual files. CPAP Clarity detects the Luna G3 format automatically based on the files present.
View your data. Your AHI, pressure graph, leak trends, machine settings, and therapy score appear within seconds. Your health data never leaves your device.

For a detailed walkthrough with screenshots, see how to use CPAP Clarity.

The Luna G3 stores approximately 35 nights of waveform data in a ring buffer (35 waveform files numbered .000 through .034). Older nights outside that window will show summary metadata only. Nights within the buffer show full waveform detail.

Understanding Your Luna G3 Numbers

Once your data is imported, here is what to look at first.

AHI and event breakdown

Your AHI (Apnea-Hypopnea Index) is the number of breathing disruptions per hour. For the Luna G3, this counts the obstructive apneas, central apneas, hypopneas, and unclassified apneas the firmware records; RERAs appear in your event breakdown but are excluded from the AHI, matching the device. For a full explanation of what AHI means and how it is classified, see what is AHI.

An AHI below 5 events per hour is the commonly used well-controlled mark (the AASM threshold). If your AHI is consistently elevated, or if you notice a sudden change, that is worth discussing with your sleep physician. Do not adjust your pressure settings based on your data alone. Settings changes are a clinical decision.

Paying attention to the split between obstructive and central events matters. Obstructive events suggest the airway is collapsing and may respond to pressure adjustments. Central events have a different origin and require a different clinical approach. CPAP Clarity shows both in your event breakdown.

The Luna G3 event mapping is verified count-for-count, night by night, against OSCAR's reading of a contributor's card across all five event types (obstructive, central, hypopnea, unclassified, and RERA). If your event breakdown still looks very different from what a sleep study or another tool showed you in the past, please let us know.

Leak rate

The Luna G3 records leak in liters per minute. Small amounts of intentional leak through mask vents are normal and expected. Unintentional leak from a poor seal is what you want to minimize. CPAP Clarity flags nights where leak was elevated and shows trends over time.

If you are seeing persistent high leak, the most common causes are mask fit, headgear tension, and sleeping position. Try adjusting the headgear before concluding you need a different mask. If the problem continues, bring your leak data to your provider.

Pressure behavior and Reslex

The Luna G3's AutoCPAP algorithm adjusts pressure based on detected events. Watching the pressure curve tells you how hard the machine was working. A flat, low-pressure night with good AHI means the machine found a comfortable working range. A high-pressure night with persistent events may mean the machine is working at its upper limit.

Reslex is BMC's pressure relief feature, equivalent to ResMed's EPR. It lowers pressure when you exhale, making the therapy feel more natural. The Luna G3 offers three levels of Reslex. For a full explanation of how pressure relief works and what the levels mean, see understanding EPR.

Luna G3 Settings Explained

CPAP Clarity reads your machine settings directly from the SD card. Here is what each setting means.

Mode: AutoCPAP means the machine adjusts pressure automatically throughout the night based on detected events.
Pressure range (min/max): In AutoCPAP mode, the machine operates between these two values. Your provider sets these based on your titration results.
Reslex level (1-3): Exhalation pressure relief. Level 3 provides the most relief.
Ramp time: The machine starts at a lower pressure and increases to your treatment level over this period, making it easier to fall asleep. A 15-minute ramp is common.
Humidity level: Controls the heated humidifier output. The Luna G3 supports an "Auto" mode in addition to numbered levels (1-8). Higher settings reduce dryness but can cause condensation in the hose, known as rainout.
Mask type: Tells the machine whether you are using a nasal, nasal pillow, or full face mask. This affects how the machine interprets leak measurements.
Tube type: The Luna G3 supports both a 22mm standard heated tube and a 15mm slim heated tube. The tube type is recorded in your settings.

All of these settings are prescribed by your sleep physician or configured by your provider. If something feels off about your therapy, bring your CPAP Clarity data to your next appointment.

Accessories and Essentials

The Luna G3 uses standard CPAP fittings, so most universal accessories are compatible. You do not need Luna-branded or React Health-branded replacements for most items.

Masks

Your mask determines your comfort and seal quality. The Luna G3 works with any standard CPAP mask. If you are unsure which type suits you, see full face vs. nasal masks or best masks for side sleepers.

Common mask types that work with the Luna G3:

Nasal pillow masks for minimal contact and less claustrophobia
Nasal masks for a balance of seal and comfort
Full face masks if you breathe through your mouth

SD cards and readers

The Luna G3 uses a standard SD card. Any name-brand card up to 32 GB works. See best SD card for your CPAP for specific recommendations.

If your computer lacks a built-in reader, a USB-C SD card reader is an inexpensive addition.

Cleaning and maintenance

Standard CPAP cleaning practices apply to the Luna G3. Clean the mask cushion daily with mild soap, replace filters on schedule, and clean the humidifier chamber weekly.

Helpful supplies:

CPAP cleaning wipes for quick daily mask maintenance
Replacement filters (check your Luna G3 manual for the correct size)
CPAP hose if yours needs replacing

For a complete maintenance routine, see how to clean your CPAP.

Luna G3 vs BMC E-20A vs ResMed AirSense 11

Feature	Luna G3	BMC E-20A	ResMed AirSense 11
Manufacturer	BMC Medical (React Health dist.)	BMC Medical	ResMed
Type	AutoCPAP	AutoCPAP	AutoCPAP
Pressure relief	Reslex (3 levels)	Reslex (3 levels)	EPR (3 levels)
Data channels	Pressure, leak, RR (derived, newer firmware)	Pressure, leak, RR, TV, MV, I:E	Pressure, leak, RR, TV, MV, flow limit, snore
AHI event breakdown	OSA, CSA, HYP, UA	OSA, CSA, HYP	OSA, CSA, HYP, UA
Companion app	PAP Link (optional)	None	myAir
SD card data	Yes	Yes	Yes
CPAP Clarity support	Yes	Yes	Yes

The key data difference is per-second respiratory physiology: the BMC E-20A exposes respiratory rate, tidal volume, minute ventilation, and I:E ratio. The Luna G3's newer firmware generation exposes respiratory rate, derived from the breath-by-breath log on the card, but not tidal volume, minute ventilation, or I:E ratio. The ResMed AirSense 11 adds flow limitation and snore detection on top of that.

For most users evaluating their therapy, AHI, leak, and pressure are the primary metrics. All three devices provide those. The Luna G3 is a capable AutoCPAP machine, and CPAP Clarity gives you access to every data channel the firmware exposes.

The Luna G3 is also closely related to the BMC G3 A20, which uses older firmware and is supported through CPAP Clarity's existing BMC parser. If you are unsure which device you have, check the firmware version in your machine's settings menu or on the label on the bottom of the unit. For a broader comparison including Lowenstein Prisma Smart and Philips, see our CPAP machine comparison.

When to Talk to Your Doctor

Your therapy data is most valuable when you share it with your sleep physician. Patterns worth bringing to your next appointment:

AHI consistently above 5 events per hour. Your pressure range or mode may need adjustment.
A significant increase in central apneas. Central events do not respond the way obstructive events do. Your provider needs to know about this pattern.
Elevated or rising leak trends despite trying different mask fits or headgear adjustments. You may need a different mask type or size.
Persistent daytime sleepiness despite consistent nightly use and good AHI. Other factors may be affecting your sleep quality.

CPAP Clarity generates PDF therapy reports formatted for your provider to review. Download one before your appointment. Concrete numbers lead to better conversations than general impressions. For tips on presenting your data effectively, see preparing CPAP data for your doctor.

Get Started

If you have a Luna G3 and have never seen your detailed therapy data, now you can. Pull your SD card, open cpapclarity.com, and drop in the folder. It takes under a minute, it is completely free, and your health data stays on your device.

Analyze your Luna G3 data now, free and private →

Luna G3 CPAP Review: Data Access Guide