Why have luminance contrast?
The Luminance Contrast Assessment Tool (LCAT) is suitable for comparing luminance reflective values (LRV) to see if compliance can be achieved.
Where it is necessary to achieve sufficient luminance contrast between building elements, this can usually be achieved by using very dark or very light materials.
Luminance contrast between building elements or TGSIs is the difference in the amount of light reflected (luminance reflectance) from the 1st surface compared to the amount of light reflected from the 2nd surface.
The intent of a suitable luminance contrast is to ensure that accessible features are identifiable for everyone, including those with reduced vision.
What is the minimum luminance contrast ratings?
Any accessible building element must have a minimum luminance contrast of 30% compared to the amount of light reflected from the second building element (usually the backing surface).
TGSIs on stair and ramp landings require a minimum luminance contrast of:
- 30% for tactile tiles (in one solid colour),
- 45% for discrete indicators (being single coloured individually installed cones), or
- 60% for discrete composite indicators (in two colours).
In some places, it may be necessary to test TGSIs or building elements when wet and dry.
What are the luminance contrast test methods?
AS 1428.1 (2009) Appendix B (‘informative’ guidance material for building elements), and AS/NZS 1428.4.1 (2009) Appendix E (‘normative’ requirements for TGSIs), set out two methods for measuring the LRV, the first in a laboratory, the second using an on-site methodology.
*** Note – The LRVs to be entered into the LCAT must have been determined using laboratory testing methodology in an approved method using the correct instrumentation as outlined in Appendix B of AS 1428.1 (2009) and AS/NZS 1428.4.1 (2009) Appendix E. ***
For laboratory testing to fully comply with:
- the ‘informative’ guidance in AS 1428.1 (2009) Appendix B; and
- the ‘normative’ Deemed-to-Satisfy’ requirements of AS/NZS 1428.4.1 (2009) Appendix E;
the LRV must have been measured using either a tristimulus colourimeter or a spectrophotometer, both with a diffused illumination of d/0 geometry, using CIE Standard Illuminant D65. The instrument has to be capable of measuring absolute CIE for Yxy to be calculated. The measured LRV is defined by the tristimulus value Y. The chromaticity coordinates x and y provide an indication of the colour.
This test method in both AS 1428.1 (2009) and AS/NZS 1428.4.1 (2009) is not suitable for measuring the LRV of translucent materials or illuminated objects. It is less applicable where the measured surface is not uniformly coloured, and in such cases, additional results will be taken to average out the results.
Is all luminance contrast testing equipment the same?
As highlighted above, AS 1428.1 (2009) Appendix B (‘informative’ for building elements), and AS/NZS 1428.4.1 (2009) Appendix E (‘normative’ requirements for TGSIs), set out two methods for measuring the LRV, the first in a laboratory, the second using an on-site methodology:
- Laboratory testing equipment includes a spectrophotometer or a tristimulus colourimeter
- Equipment for the onsite methodology includes the use of a photometer on a tripod.
Please also note we understand that all spectrophotometers do not have the correct geometry specified in the access standards (being d/0 which means that the diffused illumination and normal viewing has the measuring part of the equipment at 0 or zero degrees) and any results from equipment not using a d/0 geometry obtained using this type of equipment should be treated with a little caution in terms of meeting the prescriptive requirements of AS/NZS 1428.4.1 (2009), however, we understand that this geometry is more aligned to how the human eye perceives surfaces (and is an approach accepted overseas).
When checking any LRV certificates from testing agencies, please consider:
- The LRV data obtained using a tristimulus colourimeter or spectrophotometer has the correct geometry in the equipment. Some testing equipment does not have a d/0 geometry and actually have a 45/0 (meaning the instrument illuminates at an angle of 45 degrees and measures from 0 degrees).
- There are some colourimeters being used by industry that do not comply with the requirements of the access standards and do not use CIE Standard Illuminant D65.
However, it is also worth noting that the British Standard, BS 8300-2009, in Appendix B (also ‘informative’ only) specifies the 0°/45°geometry, being consistent with some equipment commonly used (Clause B2.2).
You can get a copy of the LCAT here