How should I hold the camera?
How you normally do.
At what height should I take photo?
A comfortable height for you.
Does the angle affect the reading?
Yes. That is why it is important to take the photo in a way that represents your viewing angle.
What are typical viewing angles?
- For standards stairs, between 30o-50o
- For ramps 0o – 30o
Should I zoom the photo?
There is no need to zoom the photo, unless the subject to be measured is very small.
Should I use the flash?
No, unless you wish to replicate a higher level of illumination for your contrast measurements. (Increasing light levels improves the luminance).
How can Get Luminance assess textured, curved, and uneven coloured surfaces?
The photograph shows what it sees, (or not), reflecting conditions experienced by users. It captures shadows, glare and reflections. For example, a curved surface will capture light differently and might be partially shaded. The information in the selected area is analysed, and variations are averaged out to provide a measure of luminance as it is experienced.
Which luminance contrast method should I use?
Different countries have adopted different approaches to measuring luminance contrast. The choice of calculation method can have a significant impact on the contrast result. Similarly, each country has set minimum requirements depending on the specific application. Some Standards require a minimum lux level, differences for large areas, small areas, hazards. Others have different requirements for different types of feature, such as tactile ground surface indicators (guiding blocks) and so on. It is important to use the calculation method described in standards within your jurisdiction.
How much confidence can I have in the results?
The algorithm to calculate luminance, as seen by the camera, has been validated. Results may vary due to:
- Chosen luminance contrast calculation method
- Prevailing light conditions
- Device dependency
Is Get Luminance a photometer?
A photometer can be defined as an instrument for measurement of intensity of visible light, so not strictly, but we can derive photometer readings in CD/m2 if we measure lux levels as well. This was one of the validation methods for the algorithm.
Is Get Luminance a colorimeter?
Not strictly, but Get Luminance uses the image data to derive luminance. The main difference is that colorimeters are typically specular component inclusive with a controlled light source and measure pure colour. Get Luminance is specular component exclusive, which means it includes for prevailing light conditions and measures luminance from the colours as people experience them, for example a ‘pure white’ may look grey in shaded conditions.
Does Get Luminance provide an Australian Standard approved methodology?
Not obviously, but yes. As per AS 1428.4.1 clause E3.3(e) “A more accurate calculation might be based on the relative proportions of each colour (where these proportions might be determined by image analysis techniques)”. Get Luminance uses this approach.
What does device dependent mean?
Device dependent means that the readings obtained will vary between individual devices. This is just like a camera, video recorder, TV display, computer monitor etc. Indeed, it is also true of any photometric and colormetric equipment which work to agreed error levels and require calibration.
Should I include a white test sample to ‘white-correct’?
There is no need to white-correct luminance values.
Do I need professional advice?
Get Luminance can be used to help determine if further advice is needed and is not a substitute for the expertise of built environment professionals, access consultants or specialist testing companies.
Will I still need to obtain luminance contrast data from companies with expensive photometer or tristimulus colorimeters?
The purpose of Get Luminance is to provide an everyday tool and an empirical basis for instructing further testing as needed.