Obstacle detection

Investigating the effects of lamp type and luminance

Dates: June 2007–May 2008
Staff: Steve Fotios, Chris Cheal
Funding: Philips Lighting Ltd.

This work examined the effect of light source, illuminance and observer’s age on the ability to detect an obstacle simulating a raised paving slab, presented for 300 ms in six different positions relative to the line of fixation. The light sources used were the high pressure sodium, MASTER City White 942 (4200K) and MASTER CosmoWhite (2700K) discharge lamps.

The illuminances used were 0.2, 2.0 and 20 lux, measured on the paving surface. These illuminances cover the range of those recommended for subsidiary streets and ensure the human visual system is operating in the mesopic state. Two age groups were used as observers, one group being less than 45 years of age and the other being more than 60 years of age. The positions of the obstacle varied from 0 to 42 degrees to the right of fixation and 8 to 23 degrees below fixation.

Test apparatus
Test apparatus: this is a side elevation with the panel removed to expose the interior.

The data collected were used to determine the height of the obstacle above the paving surface required for fifty percent detection at each position, for all combinations of light source, illuminance and age. From these detection heights it was determined that:

  • Obstacle detection was influenced by the illuminance, the 50% detection height being less at 20 lux than at 0.2 lux.

  • At 0.2 lux, the 4200K MASTER City White light source gave the smallest 50% detection height while the high pressure sodium light source gave the largest. There were no statistically significant differences between the 50% percent detection heights for the three light sources at 2.0 and 20 lux.

  • The young observers showed the smaller 50% detection height at 0.2 lux but at 20 lux there was no difference in 50% detection height for the two age groups.

Graph illustrating data described above


  • Fotios SA and Cheal C, Obstacle detection: a pilot study investigating the effects of lamp type, illuminance and age, Lighting Research and Technology, 2009; 41(4); 321-342.

  • Fotios S and Cheal C, Lighting spectrum and obstacle detection for pedestrians, Lux Europa, Istanbul, 2009, 1171-1176.

  • Fotios S and Cheal C, Lighting spectrum and obstacle detection for pedestrians, Proceedings of the 6th Lux Pacifica, Bangkok, 23-25 April 2009, 107-110.

  • Fotios S and Cheal C, Lamp spectrum, Illuminance and the Pedestrian’s Ability to Detect Obstacles, Lighting Journal, 2008; 73(6); 35-41.