The Glamox Brightness Sensitivity Test

Have you noticed that the light from modern LED luminaires seems brighter than that of conventional lighting? Especially if the luminaires are equipped with cool white LEDs. If you put a lux meter below the LED and conventional installation, the lux level may be exactly the same.
This discrepancy in measured lighting levels is explained by the fact that the measurement equipment is adjusted to the human eye’s sensitivity for warmer colours. Humans perceive cool white light as brighter than the warm white and this is not always captured with measurement equipment and lighting standards. A cool white light source would therefore score “lower” on lighting measurements. At Glamox we believe that adjusting light levels from cool white lighting installations to better match peoples’ perception of brightness will lead to lower costs and energy consumption on board platforms and vessels.

test_hps-400w

Demo with 400 W High Pressure Sodium lamps in flood lights. Average illuminance level: 286 lux.

test_led-160w

Demo with 160 W LED luminaires. Average illuminance level: 95 lux. The installation seems equally bright or brighter to the human eye. Both pictures were taken with identical parameters: Exposure time 1/2 sec; F-Number: 8; ISO speed: 400.


The test
Glamox has initiated a test to document people’s sensitivity to different light sources. In the test rig, two chambers are illuminated with two different light sources with two different shades of white light. We call this the colour temperature of the light, where a warm white colour indicates a yellowish light and a cool white colour is more bluish.

brightness_sensitivty_chamber

Test chamber with HPS lamp to the left, LED to the right.

The test persons were asked to adjust the perceived brightness level (i.e. spatial brightness) inside the chamber illuminated with a cool white (5000 kelvin) LED source to where it matched the light level of the chamber with a 1900 kelvin high pressure sodium lamp. The difference between the measured lux levels is expressed as a percentage. The result of the test was that people adjusted the LED light and its corresponding illuminance to 55% (on average) of the illuminance in the HPS chamber. (n=118, std. dev.: 39%). A conversion factor of 55% is suggested based when comparing a cool white LED installation to a HPS installation. The full test report is available to customers on demand.


What would a “brightness adjusted” installation look like?

ship_hps

Installation with 100 lux, achieved by 12 x 400 W HPS flood lights.

ship_led

Installation with 55 lux, which is the ratio between the conversion factors of HPS and cool white LEDs, achieved by 10 x FX60 160 W LED flood lights. The two installations will seem equally bright to the observer.

Other references
Professional Lighting Guide 03 (UK) Lighting for Subsidiary Roads
Sam Berman, Lawrence Berkley Laboratory, 1991: Energy Efficiency Consequences of Scotopic Sensitivity
MS Islam, R Dangol, M Hyvärinen, P Bhusal, M Puolakka and L Halonen, 2013: User preferences for LED lighting in terms of light spectrum

Disclaimer
This recommendation of conversion factors is based on available research and Glamox experience. We bear no responsibility to any claims of poor light quality (e.g. too low or too high lux levels) when using these recommendations.


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