Smart Urban Lighting: Lecture 8 Flashcards
What are P-classes used for?
What do they depend on?
Decide on recommendations for residential areas
Depends on maximum speed, composition of traffic, intensity of use, brightness of environment
To what part of the spectrum is mesopic vision most sensitive?
Green light
Why do pedestrian guidelines focus on illuminance and not on luminance?
Luminance is relevant when there is a clear direction of view, as with a car driver focusing on the road.
Pedestrians however typically look around making luminance as the basis for recommendations infeasible
What do you know about low pressure sodium?
LPS has been used frequently in the past because of its efficiency but gives mono-chromatic yellow light.
Yellow light, therefore blue is for example not well visible. Only yellow will be seen in true color.
In mesopic vision we are more sensitive to green light
S/P ratio is?
Stands for scotopic/photopic
Light source with a high S/P will stimulate the rods more than the cones, and thus will provide better visibility in mesopic vision
What is needed for obstacle detection?
Need to know at what distance size of objects can be detected under varying lights sources and intensities
Also:
What heights of object present a real risk?
At what distance do they need to be detected in order for a pedestrian to take evasive action?
Metal halide outperformance high pressure sodium in low intensity conditions. Why?
Because only with mesopic vision will the S/P ratio make a difference (because on higher reliance on rods in dim conditions) especially as objects were presented
What is the problem with self-reports?
Biased, range - bias
What is range bias?
And why does it occur?
We cannot trust scale labels, because whether a environment is safe or unsafe depends on what other environments are in the set that is evaluated
People have difficulties with absolute judgements
They rely on the previous stimuli in the set as a reference
Tendency to use the full scale when appraising a stimulus set
Why does the effect of lamp type with a differing S/P ratio not matter for face recognition?
Probably because when detecting a face, the image falls on the fovea, where rods are largely absent
Why green street lighting?
By providing most light in the mesopic-optimal green spectrum energy is saved without comprising visibility
What color is often mixed in with green street lighting and why?
Red light is often mixed in a bit so that road signs can also be easily read
What is the problem with green street lighting?
Under mesopic conditions we are more sensitive to the green part of the spectrum, however, this is not reflected in illuminance measurements with a lux meter (based on PHOTOPIC standard observer)
As a result, these luminaires seem to provide less visibility, thus requiring higher intensity to meet lighting recommendations
What type of lighting do people prefer? distant visible, everywhere equally visible, of nearby visible
Nearby visible is preferred
People prefer light where they walk over having light in the distance
Surprising finding in study at de Zaale about close/far lighting?
Having less sight in the distance increases how peoples perception of how well they could see what was going on. Perhaps because threats are typically nearby, that’s why people want to see whats happening nearby?
