Quick Answer: Light intensity falls off sharply with distance, so moving from six inches to twelve inches from a panel can cut the delivered energy by roughly three quarters. Since dose is intensity multiplied by time, distance is the more powerful lever - and it is the one almost nobody measures. Fix your distance first, then set the time to reach your target dose. A consistent distance is what makes sessions comparable at all.

Most home users vary their distance by a foot between sessions without noticing.

That alone makes their results uninterpretable.

How much does distance really change the dose?

Enormously - and the relationship is not linear.

Light intensity from a source spreads out as it travels, so the energy landing on a given area drops rapidly with distance. For a point source the relationship is an inverse square: double the distance and intensity falls to about a quarter.

Panels are not perfect point sources, so real-world falloff is somewhat gentler - a large panel behaves more like an array of sources and holds intensity better up close. But manufacturer measurements consistently show large drops: typical figures might be well over 100 mW/cm² at six inches falling to a fraction of that at twenty-four.

Session length only scales linearly. Doubling your time doubles your dose. Halving your distance can quadruple it. That asymmetry is the whole point.

Which means the common practice of standing wherever feels comfortable and running a ten-minute timer produces wildly inconsistent doses from session to session.

And crucially, more is not automatically better. Photobiomodulation shows a biphasic dose response - too little does nothing, an optimal range produces the effect, and too much can reduce the benefit. This is one of the few areas where overdoing it genuinely works against you, which makes accidental dose variation more consequential than it would be otherwise.

How do I set a distance and time deliberately?

Use the manufacturer’s irradiance data, then do the arithmetic once.

Find the irradiance figure for your panel at a stated distance. Reputable manufacturers publish this - typically in mW/cm² at six, twelve, and twenty-four inches. If your panel has no published figures, that is itself informative about the manufacturer.

Decide a target dose. Commonly cited ranges in the literature sit somewhere around 3 to 60 J/cm² depending on the application, with lower doses typical for surface applications and higher for deeper tissue. This is an area where the research is still developing and the ranges are wide.

Then use the relationship: dose (J/cm²) = irradiance (mW/cm²) × time (seconds) ÷ 1000.

A worked example. If your panel delivers 100 mW/cm² at twelve inches and you want 12 J/cm², you need 120 seconds - two minutes. At twenty-four inches the same panel might deliver 25 mW/cm², requiring eight minutes for the same dose.

Notice what that means: the same target takes two minutes or eight, depending only on where you stand. Someone doing ten minutes at six inches and someone doing ten minutes at two feet are running completely different protocols.

Pick one distance and mark it on the floor. Tape on the floor is the single most useful thing you can do for consistency, and it takes ten seconds.

What else changes the delivered dose?

Four things, all commonly overlooked.

Angle. Light hitting a surface at an angle spreads the same energy over a larger area, reducing intensity. A body part angled away from the panel receives measurably less than one facing it squarely. For a targeted area, face it directly.

Coverage area versus panel size. A small panel does not evenly illuminate a large body area - intensity is highest directly in front of the panel centre and falls toward the edges. Treating a large area with a small panel means most of it gets a fraction of the stated dose.

Clothing and anything in between. Fabric blocks a large share of the light. Bare skin is required for the target area. Even thin clothing substantially attenuates the delivery.

Wavelength and what you are aiming at. Red light around 630 to 660nm penetrates less deeply and is used for surface and skin applications; near-infrared around 810 to 850nm penetrates further and is used for deeper tissue. A panel with both gives you options; matching wavelength to target matters as much as dose.

And panel output declines over its life, gradually, without any visible change. LED output degrades over thousands of hours, so a panel several years into heavy use is delivering less than its specification.

Practical version: bare skin, facing the panel, at a marked distance, for a timed period. Four controls, all free.

Myth vs Fact: Red Light Dosing

Myth: Longer sessions produce better results. Fact: The dose response is biphasic - beyond an optimal range, additional exposure can reduce the benefit. This is not a case where more is safer.

Myth: Closer is always better. Fact: Closer delivers more intensity, which is useful up to a point and can overshoot the optimal dose quickly. It also reduces the area covered. Close and short, or further and longer, can deliver the same dose - pick one and be consistent.

Myth: You can feel whether it is working. Fact: Warmth is mostly from the panel’s heat output, not from the therapeutic wavelengths. A panel that feels hot is not necessarily delivering more useful light.

Myth: All panels at the same wattage are equivalent. Fact: Total wattage says little about irradiance at the treatment surface, which depends on LED efficiency, optics, and layout. Irradiance at a stated distance is the number that matters - and the number many manufacturers avoid publishing.

Myth: Daily is better than every other day. Fact: Protocols in the literature vary widely and there is no established consensus that daily beats three to five times weekly for most applications. Consistency over months matters more than frequency within a week.

FAQ: Red Light Distance Questions, Answered

What distance should I use if my panel has no published data?

Twelve inches is a reasonable default for most mid-size home panels, and it balances intensity against coverage area. Without irradiance data you cannot calculate a dose, so consistency becomes the only thing you can control - mark the distance and keep it.

Should I move around during a session?

No, if you want a known dose. Moving changes distance and angle continuously, which makes the delivered dose unknowable. Treat one area at a fixed position, then reposition for the next.

Do I need eye protection?

These panels are bright and staring directly into them is uncomfortable and inadvisable. Most manufacturers supply goggles and recommend them for facial treatment. Closing your eyes is the minimum. If you have an eye condition or take photosensitising medication, ask a professional first - this is general information, not medical advice.

TL;DR:

• Intensity falls off sharply with distance - doubling the distance can cut delivered energy by roughly three quarters.
• Time scales linearly; distance does not. Distance is the stronger lever.
• Dose = irradiance × seconds ÷ 1000. Do the arithmetic once, then keep it fixed.
• The response is biphasic - more is not automatically better.
• Bare skin, facing the panel, at a taped distance mark, for a timed session.

Put a strip of tape on the floor tonight. That one mark makes every future session comparable.