When facing the lighting shelf in a bicycle shop, it is difficult to compare the power of brightness of lights. Some mention Lumen, others mention Lux or Candela. So let’s throw some light on the subject…
Lumen refers to the total amount of light or light energy that is radiated from a light source. This does not measure the intensity of a bicycle lamp. The intensity of the light depends on the direction. When the direction of the light is unknown it is impossible to calculate the intensity of the light.
Lux and Candela
Both Lux and Candela refer to the intensity of the light in a certain direction of the light beam.
Candela is equal in the total light beam, while the Lux-value depends on the distance of the light beam (Fig 02). In the Fig 02 the middle beam is 2000 Candela, while the amount of Lux is variable at different distances.
The formula between these two units is:
CANDELA = LUX x METER (DISTANCE)2
In most cases Lux is measured at a 10 meter distance from the light source. This means that the Candela-value can be calculated by:
1 LUX = 100 CANDELA
As can be seen in all figures the light beam of a headlamp contains several areas with different amount of Candela and Lux to create an ideal headlamp for its purpose:
To see and to be seen
When a headlamp claims to contain 20 Lux or 2000 Candela, this means that the brightest spot in the light image has 20 Lux at a distance of 10 meter (Fig 01 and 02). This amount of light is mainly directed at the road so oncoming traffic is not blinded by it (Fig 03).
To be seen
The light in the blinding area should not be higher than 2 to 2,5 Lux*. In this area the amount of Lumen is also lower (200 to 250 Lumen).
For rear lights the Candela-value is used, since very small Lux values need to be measured here. Rearlights radiate in between 1 to 4 Candela corresponding to 0,01 and 0,04 Lux*.
“A headlamp is mainly made for the rider to see the road and eventual obstacles. Spanninga uses the unit Lux as a measure of the intensity of light, as perceived by the human eye, that hits a surface. So Lux gives some indication about the lighted area in a light beam. A rearlight is made to be seen by other road users. Spanninga uses the unit Candela as a measure of luminous intensity; that is, power emitted by a light source in a particular direction. Candela says something about the intensity of the light source.”
Jacob Vellinga – Spanninga Group R&D manager
* Measured at 10 meter
Bicycle lighting has been a complicated issue for a long time. Each country uses its own regulation, which makes it difficult for users to know what they need.
In Germany the overall construction is checked and the light output and distribution is checked for either 10 Lux or 20 Lux.
In France the light distribution is checked for 4 Lux.
In Netherlands a voluntary test can be done for a RKF-classification.
In Denmark a self-certification system is used where the lights are to be checked for light distribution and a centre value of 0,04 Lux.
In Germany and France rear lights are checked for light distribution and if >2,5 Cd in the centre.
In Netherlands there is a voluntary RKF-classification.
In Denmark light are self-checked by the supplier for light distribution > 4 Cd.
For reflectors the differences are minimal. An ECE (like) reflector is accepted, except in Germany where the Z-type reflector for the carrier rearlight is required.
“To be able to sell bicycle lights which are allowed in road traffic, approvals are needed in several countries in Europe. Approvals give an indication about the light output and the general quality of the lighting product. Spanninga endeavours to follow the local rules in different countries in order to meet the legislation and the minimum safety requirements for bicycle lighting”.
Jacob Vellinga – Spanninga Group R&D Manager