Irradiance and wavelength get discussed. Beam angle almost never does — and it quietly determines both how much area you cover and how fast your intensity disappears.
What beam angle describes
Beam angle is the spread of light coming out of an LED, measured in degrees. It's usually defined as the angle within which output stays at or above half its peak value.
A narrow angle sends light forward in a tight column. A wide angle spreads it out. Ours is 30°, which is fairly typical for devices intended to be used at close range.
The trade-off, in one sentence
A wide beam covers more area with less intensity; a narrow beam covers less area with more intensity. There is no setting that gives you both.
This is simply how light behaves. The same optical power is either concentrated or distributed — it cannot be concentrated and distributed at once.
Why this makes distance so important
As you move away from the device, the beam widens and the same output covers a larger area. Intensity at any single point drops accordingly.
You can see it in our own measurements. Combined output goes from 58 mW/cm² at 5 cm to 40 at 10 cm to 25 at 15 cm. Same device, same settings, three very different numbers.
Which is why an irradiance figure quoted without a distance is not a specification, and why a brand quoting a 1 cm measurement against a competitor's 15 cm measurement is comparing nothing at all.
What it means when you're using one
Closer gives you more intensity over a smaller area. Further gives you less intensity over a broader one.
Neither is right or wrong — it depends on whether you're covering a small area or a larger one. Most people settle around 10 cm, which is a reasonable middle.
One practical note: intensity is highest directly in front of the centre of the array and falls off toward the edges. So the useful coverage area is a little smaller than the physical size of the device would suggest.
Why panels and handhelds differ
This geometry explains the whole comparison.
A panel has many LEDs spread across a large surface, so the beams overlap and cover a wide area at moderate intensity. A handheld concentrates fewer LEDs into a small area, so it can match a panel's intensity at the same distance while covering far less of you.
Neither is better. They're solving different problems.
Questions worth asking
What is the beam angle? If a brand doesn't know, that tells you how closely they've looked at their own product.
Was irradiance measured on-axis at the centre? It's the standard approach, but it should be stated, because a centre reading is the most flattering one available.
What area does it usefully cover at the recommended distance? Rarely published, and more relevant to how you'll actually use it than almost anything else on the spec sheet.
Read: what irradiance actually means →
Read: handheld or panel? →