Candela is one of the most useful figures when comparing high-output visual signals, but it is often misunderstood. It measures luminous intensity in a particular direction, not the total amount of light emitted in every direction.
A candela describes how intense a light appears in a given direction. That makes it particularly relevant to directional signalling equipment. A light source may have a high peak candela figure because its output is concentrated into a relatively narrow beam, while another source may spread similar total light over a much wider angle.
Lumens describe total luminous flux, broadly the total visible light emitted. Candela describes intensity in a direction. For a visual distress signal, both the available light and the way the optics distribute it matter.
Imagine the same amount of light being projected through two different optical systems. One concentrates it into a tight beam and achieves a high peak intensity. The other spreads it across a wider field and produces a lower peak figure. The first may be brighter on target but harder to aim from a moving vessel. The second gives more coverage but less intensity at any single point.
This is why a candela number should be considered alongside horizontal and vertical beam angles.
Independent photometric testing of the full-size UltraFlare Daylight measured peak luminous intensity above 40,000 candela. Its optical system is designed around a 45 degree horizontal display and 15 degree vertical display, balancing intensity with useful angular coverage.
Not by itself. Real-world visibility depends on daylight level, background contrast, atmospheric conditions, observer height, line of sight and whether the observer is actively searching. A responsible assessment should avoid converting candela into one guaranteed distance for all conditions.
For a fuller picture, read our guide to daylight visibility and why beam angle matters. Our Technology page explains the independent testing in more detail.