Basic terms in lighting technology

How light is measured

When purchasing a halogen light H3 55 watts, you know from experience how much light you get on the ground. However, watts measure only the energy consumption, it cannot be used as an indication of how much light you will receive on the ground. Light is measured using other terms such as:

Candela

which measures luminous intensity (cd)

Lumen

which measures luminous flux (lm) of the LED work light.

There are 3 different lumen outputs: theoretical, cold and effective (or measured). The losses caused by the optical system and the heat effects of the LED chips are not deducted from the theoretical lumen output. TYRI measures effective lumen output when a LED work light after 30 – 45 minutes has reached its operating temperature. The cold lumen output has decreased because all LED Chips have a lower efficiency when the temperature is higher. The lumen output is thus reduced by 5 % due to the heat. The losses due to the optical system are about 20 – 25 % which means that the effective lumen output is in total about 70 – 75 % of the theoretical lumen output.

Lux

which measures the amount of light output in a given area

Important

When looking at the light from two light sources with your eyes only, it is not possible to decide how much more light one makes compared to the other. It is possible to correctly compare the light sources, if you measure the lux in a given area. However, you will need to ensure that the area of comparison is the same. If one area is larger than the other, the lux value will decrease, and the comparison will be incorrect. You also need to consider the impact of a cold white colour temperature – see next point below on Colour Temperature for more information.

Colour Temperature

If you compare a cold white colour temperature (far over 6000 K) with warmer colour temperatures (5700 K and less) it will give the impression that the visibility on the ground is better with cold white colour temperature. However, it is very difficult to work in cold white colour temperatures for long periods of time, as it causes the operator eye fatigue and headaches. In addition, cold white colour temperatures create more glare and reflections from snow, dust, small particles, and rain.

Spectral Colours

For the creation of a rainbow, sunlight and raindrops are necessary. The light ray penetrates the rain drop and is broken. The so-called spectral colours are separated and totally reflected on the back of the rain drop. They are broken again and then they leave the rain drop. The colours that are seen on the rainbow are red, orange, yellow, green, blue/indigo and violet.

Colour temperatures of LED work lights are decided by mixing the seven spectral colours. If the percentage of the red colour is larger than the others, the colour temperatures is warmer (warm white to yellow). If the percentage of the blue colour is larger than the others the colour temperatures is colder (cold white to blueish).

And did you know – White contains all colours!

For more information on CRI and Colour temperature click here.

The Human Eye

The human eye can be compared with a camera. Light penetrates the pupil and is broken through the cornea, the lens, and the vitreous body. On the retina a miniaturised upside-down image is created which is captured by the rods and the cones. Brightness values are differentiated by the rods and colour is differentiated by the cones. Human eyes deteriorate over time which is why younger people have more perceptions of light than older people.

Target values

Forklift trucks: 30 – 50 lux
Tractors: 40 – 60 lux
Forestry machines: 60 – 80 – 120 lux
Construction machines: 40 – 60 – 100 lux
Drilling rigs: 60 – 120 lux
Mining machines: 60 – 120 lux

Reference value:

A halogen work light H3 55 watts with around 1000 – 1100 effective (measures) lumen, symmetrical light pattern and 10 m work area reaches between 15 and 20 lux.