The optimal LLLT dose for hair loss falls between 4 and 6 J/cm2 per session based on published research. Getting this dose right is the difference between effective treatment and wasted time, because the photobiomodulation response follows a biphasic curve where too little does nothing and too much can actually inhibit growth.
This content is for informational purposes only and does not constitute medical advice.
What Photon Count Means for Hair Growth
Photon count refers to the total light energy delivered to your scalp during an LLLT session, measured in joules per square centimeter (J/cm2). This measurement, also called fluence or energy density, determines whether your laser cap session reaches the therapeutic threshold.
Think of it like medication dosing. Taking half a pill might not help. Taking the right dose works. Taking ten pills is harmful. LLLT follows the same logic, just with photons instead of molecules.
How to Calculate Your Laser Dose
Every LLLT device has three key specifications that determine the dose it delivers:
| Specification | Unit | Where to Find It |
|---|---|---|
| Power output | Milliwatts (mW) | Device manual or product listing |
| Number of diodes | Count | Device manual or product listing |
| Treatment area coverage | cm2 | Manufacturer specification |
The dose calculation formula:
Dose (J/cm2) = Total Power (mW) x Time (seconds) / Treatment Area (cm2) / 1000
Example Calculations
Laser cap with 272 diodes at 5mW each, 600cm2 coverage, 30-minute session:
- Total power: 272 x 5 = 1,360 mW
- Time: 30 x 60 = 1,800 seconds
- Dose: 1,360 x 1,800 / 600 / 1,000 = 4.08 J/cm2
This falls right in the optimal range of 4 to 6 J/cm2.
Laser comb with 12 diodes at 5mW each, 20cm2 coverage, 15-minute session:
- Total power: 12 x 5 = 60 mW
- Time: 15 x 60 = 900 seconds
- Dose: 60 x 900 / 20 / 1,000 = 2.7 J/cm2
This is below the optimal range. You would need a longer session to reach 4 J/cm2.
| Device Type | Typical Total Power | Session Time for 4 J/cm2 | Session Time for 6 J/cm2 |
|---|---|---|---|
| Full laser cap (272 diodes) | 1,360 mW | 26 minutes | 40 minutes |
| Half-cap (148 diodes) | 740 mW | 49 minutes | 73 minutes |
| Laser comb (12 diodes) | 60 mW | 22 min per zone | 33 min per zone |
| In-office panel | 5,000+ mW | 7 minutes | 11 minutes |
Step 1: Find Your Device Specifications
Check your laser cap or comb manual for three numbers: total power output (or per-diode power and diode count), and treatment area. If the manufacturer does not publish treatment area, estimate based on the device's physical size. A full laser cap covers approximately 500 to 700 cm2.
If your device only lists "total power" as a single number, use that directly in the formula.
Step 2: Calculate Your Current Dose
Plug your numbers into the formula above. Most users discover they are either underdosing (session too short) or within range. Overdosing with consumer devices is uncommon because their power output is relatively low, but it is possible with extended sessions on higher-power caps.
Step 3: Track Density Response at Your Current Dose
Before changing anything, take weekly density readings on myhairline.ai for at least 12 weeks at your current dose. This establishes your baseline response curve at this specific energy level.
Log each LLLT session in myhairline.ai with the date, duration, and calculated dose. This creates a dataset linking dose to density outcomes that you can analyze later.
Step 4: Adjust and Compare
If your current dose falls outside the 4 to 6 J/cm2 range, adjust your session time. If it is within range but you see no response after 16 weeks, try moving to the other end of the range (increase from 4 to 6 J/cm2 or decrease from 6 to 4 J/cm2 if you suspect overdosing).
Rules for dose adjustment:
- Change only session duration, not frequency
- Run each new dose for at least 12 weeks before evaluating
- Keep all other variables constant (treatment products, application schedule)
- Take density readings on the same day and under the same conditions
Step 5: Find Your Frequency Sweet Spot
Dose per session is only half the equation. Session frequency matters too. Most manufacturer protocols recommend 3 sessions per week on non-consecutive days. Published research supports this frequency, though some studies show benefit with every-other-day use.
| Frequency | Weekly Total Dose (at 5 J/cm2/session) | Evidence Level |
|---|---|---|
| Daily | 35 J/cm2/week | Limited research; possible overdosing |
| Every other day | 17.5 J/cm2/week | Some supporting studies |
| 3x per week | 15 J/cm2/week | Most supported by published research |
| 2x per week | 10 J/cm2/week | May be subtherapeutic |
| 1x per week | 5 J/cm2/week | Likely insufficient |
Track your density at one frequency for 12 weeks, then adjust if needed. The goal is to find the minimum effective dose that produces measurable density improvement without overshooting into the inhibitory range.
Common Dosing Mistakes
Mistake 1: Assuming longer is better. A 60-minute session on a high-power cap can push you into the inhibitory dose range above 10 J/cm2. Follow the calculated session time for your device.
Mistake 2: Skipping sessions and compensating with longer ones. Two 30-minute sessions do not equal one 60-minute session in biological effect. The biphasic response resets between sessions. Consistency matters more than making up missed time.
Mistake 3: Ignoring device degradation. LED and laser diodes lose power output over time. A cap rated at 5mW per diode may output 4mW after 2 years of use. If your response declines over time despite consistent use, diode degradation could be the cause.
Combining LLLT With Other Treatments
LLLT works through a different biological pathway than medications. Finasteride (80 to 90% halt further loss, 65% regrowth) blocks DHT. Minoxidil (40 to 60% regrowth) acts as a vasodilator. LLLT increases cellular ATP production. These mechanisms do not compete, which means combining them produces additive benefits.
PRP therapy ($500 to $2,000 per session) also pairs well with LLLT. PRP delivers growth factors that stimulate blood vessel formation, improving oxygen delivery to follicles. Better oxygen supply enhances the ATP production pathway that LLLT activates.
For detailed session-by-session tracking guidance, see tracking LLLT progress over time. And for understanding how wavelength interacts with dose, the laser wavelength and hair density tracking guide covers the full spectrum.
Start tracking your LLLT dose response with a free density baseline at myhairline.ai/analyze.
This article is for informational purposes only and does not constitute medical advice. Consult a dermatologist before starting any LLLT protocol.