Quick Answer: Light intensity falls off roughly with the square of distance, so moving from 6 inches to 12 inches cuts the energy reaching your skin to about a quarter. Session length adds dose linearly, distance changes it geometrically. Most home users are too far away and compensate with long sessions, which is the least efficient way to reach an effective dose — and past a point, more time stops helping.

You have been doing twenty-minute sessions faithfully and seeing little. Meanwhile someone else does eight minutes and reports a difference.

The variable nobody measures is how far away they sit. It matters more than the number on your timer, and it is the easiest thing to get wrong.

Here is how the arithmetic actually works.

Why does distance matter so much more than time?

Because time adds dose in a straight line while distance changes it geometrically.

Dose is intensity multiplied by time. The energy delivered to your skin depends on the panel’s irradiance at your position — measured in mW/cm² — times how many seconds you sit there.

Irradiance falls with roughly the square of distance. Move from 6 inches to 12 inches and intensity drops to approximately a quarter. Move to 24 inches and you are near a sixteenth. To match a 10-minute session at 6 inches, you would need roughly 40 minutes at 12 inches — and that is if nothing else changed.

Real panels are not perfect point sources, so the fall-off is not exactly squared — larger panels fall off somewhat more gently at close range. But the direction and rough magnitude hold, and every manufacturer’s own irradiance chart shows it dramatically.

Which means distance is your dose dial. Set the distance deliberately, then use time for fine adjustment. Doing it the other way round is why so many routines underperform.

So should you just get as close as possible?

No — there is a real ceiling, and past it more is not better.

Biphasic dose response is well described in this field. Too little light produces no effect; an effective range produces benefit; substantially more can reduce the benefit again. This is one of the few areas where more is genuinely not better.

Most protocols land in a similar range. Published work commonly uses somewhere around 3 to 60 J/cm² depending on target and depth, with skin-level applications typically at the lower end. Your panel’s manual should state its irradiance at given distances, which lets you calculate rather than guess.

Work out your own number once. Dose in J/cm² equals irradiance in mW/cm² times seconds, divided by 1,000. If your panel delivers 100 mW/cm² at 6 inches, 10 minutes gives 60 J/cm². That single calculation replaces a lot of guesswork.

Heat is your practical limit. If the panel feels uncomfortably warm, you are close enough that thermal effects are entering the picture, which is a different mechanism and not the one you are after.

What should a sensible home routine look like?

Fixed distance, moderate time, consistent frequency — in that order of importance.

Pick a distance and mark it. Tape on the floor, a chair in a set position, anything repeatable. An unmeasured distance makes every other variable meaningless, and this is the single most common flaw in home routines.

Use the manufacturer’s irradiance figure for that distance. Then set your time to land in the range you are targeting. For most skin-level goals with a reasonable panel, that is 8 to 15 minutes.

Three to five sessions a week. Frequency and consistency matter more than any individual session. Daily is generally fine; sporadic is what fails.

Do not stack more time when results are slow. Give a consistent protocol 8 to 12 weeks before changing anything. If you then adjust, change distance or frequency, not just duration.

Keep the target area consistent too. Panels have a limited effective coverage area. Treating a different spot each session at long range delivers a low dose everywhere and an effective dose nowhere.

5 Mistakes Everyone Makes With Home Panels

1. Never measuring the distance. Sitting wherever is comfortable means your dose varies session to session by a factor of several. Mark the spot.

2. Compensating with very long sessions. Forty minutes at three feet is a lot of time for a small dose, and the biphasic response means simply extending time is not a reliable substitute for adequate intensity.

3. Ignoring the panel’s own irradiance chart. Manufacturers publish these. It takes two minutes to read and it converts your routine from guesswork into arithmetic.

4. Trying to treat the whole body with a small panel. A small panel covers a small area effectively. Pick one target region and be consistent rather than sweeping.

5. Changing something every two weeks. With an 8 to 12 week timeline, frequent adjustment means you never learn what any version does. Pick a protocol and hold it.

This is general information, not medical advice. Follow your device’s eye-safety instructions, and check with a healthcare professional before use if you have a photosensitizing condition or take photosensitizing medication.

FAQ: Red Light Dosing Questions, Answered

How do I find my panel’s irradiance if the manual does not say?

Check the manufacturer’s website or product page, where it is usually given at 6, 12, and 24 inches. If no figure is published anywhere, that is worth noting about the product — it is the single most important specification a panel has.

Is closer always more effective within the safe range?

Up to a point. Closer means higher intensity for a shorter time, which is efficient. But very close positioning reduces the area covered and increases warmth, so a moderate distance with a slightly longer session is often more practical.

Does it matter what time of day I use it?

For most goals, consistency matters more than timing. If you are using it around training, the current evidence is mixed and the effect of timing appears small relative to getting the dose and frequency right.

TL;DR:

• Intensity falls off roughly with the square of distance; time adds dose linearly. Distance is the dominant variable.
• Going from 6 to 12 inches cuts intensity to about a quarter — you would need roughly four times the session to match it.
• More is not better: the dose response is biphasic, so extending sessions indefinitely can reduce the benefit.
• Mark a fixed distance, read your panel’s irradiance figure for it, and calculate dose as mW/cm² × seconds ÷ 1,000.
• Aim for 8 to 15 minutes, three to five times a week, on a consistent target area.
• Hold a protocol for 8 to 12 weeks before changing anything, and adjust distance or frequency rather than piling on time.

The reason two people get different results from the same panel is usually not the panel. Measure the distance once, do the arithmetic once, and your routine stops being a hopeful ritual and becomes a dose you can actually evaluate.