Glare rating (GR) and UGR difference

Posts: 14
Joined: Sat Feb 09, 2019 7:09 pm

Glare rating (GR) and UGR difference

Post by » Fri May 31, 2019 9:03 am

What is the difference in GR and UGR?

As both options are available in calculation,I get confused!

Also,when should I select GR and when should I select UGR ?

What are their expected values (minimum values) for sports lighting ?



Posts: 1996
Joined: Wed Mar 07, 2012 3:07 pm

Re: Glare rating (GR) and UGR difference

Post by Csuleiman » Fri May 31, 2019 9:21 am

Hello Gaurav,

Below you will find an abstract of our DIALux manual which explains the differences between the UGR and GR calculation.

The Unified Glare Rating method (UGR) has been developed by the CIE (Commission International de l'Eclairage) in order to harmonise glare classification procedures worldwide. The method is based on a formula similar to that employed for the British Glare Index. The UGR formula can be used to assess the glare characteristics of a complete lighting system. The formula takes account of every luminaire in a given interior and also background luminance (ceiling, walls) with reference to a standard viewing point.
A standard table is available listing uncorrected UGR values for various room sizes and reflectance combinations. These values have to be corrected to take account of such factors as the luminous flux of the light sources. The final UGR scores tend to lie between 10 ("no glare") and 30 ("pronounced physiological glare").
The higher the UGR score, the greater the probability of glare. Completely different results can be achieved with luminaire locations that deviate from the standard configuration and for other viewing points. An auxiliary table provides estimated scores for the variant viewing points.

There are plans to lay down maximum UGR scores for various requirements and activities on the line of the glare quality classes used to date. The following table offers a rough conversion guide between the conventional DIN glare classes and the future UGR system.
A major enhancement of DIALux affects the UGR calculation. It can produce the following UGR results:
1) The UGR table for all luminaires with direct lighting with a spacing to height ratio (SHR) of 0.25 or 1.
2) The single sheet output and the summary of “standard rooms” (rectangular, without furniture, only one type of luminaire) show the four standard UGR values for the left wall and the lower wall viewing lengthways and across the luminaire axis. This saves doing the manual calculation with the help of the standard table.
3) You can place UGR observers at workplaces to get UGR values with respect to
a. position and viewing direction
b. all used luminaires
c. position and rotation of the luminaires
d. shadowing and reflection
4) With UGR calculation areas you get the distribution of the UGR values on an area. The calculation is comparable to the calculation of UGR observers. The output lists information about local glare problems on arbitrary places in the room.
The output of part 1 is a table of the corresponding values. For part 2 and part 3 you get single UGR values. For part 4 you get isolines and greyscale diagram, a chart and a table of the values. Possible UGR values are between 10 and 30. Smaller values are shown as <10. Larger values are shown as >30.

The draft of EN 12464-2 / EN 8995-2 intends that glare has to be avoided for outdoor working places. To ensure this, glare limits for tasks and activities are prescribed. The glare rating system (GR) is defined in the CIE publication 112:1994. For glare evaluation, the veiling luminance produced by the luminaires and by the environment are the basic criteria. The latter is handled differently by EN 12464-2. In DIALux you can choose, whether you want to use the simplified method of EN or the complete method of CIE. The simplified method approximates the veiling luminance produced by the environment (Lve) with the formula Lve=0.035 x r x Ehav x p, where r is the average reflection and Ehav the average illuminance of the “area”. Unfortunately, this “area” is not exactly defined. DIALux uses all ground elements as the “area”.
The complete method of CIE 112:1994 uses the correct veiling luminance produced by the environment in front of an observer. Here the illuminated area is considered to consist of an infinite number of small light sources. The veiling luminance produced by the environment is defined by the formula where n is the total number of small light sources. Of course, this calculation is more accurate but more time consuming too. The DIALux outputs state which method was used to calculate GR values.
To calculate GR values, DIALux provides the GR observer tab. Any GR observer can be placed just like any other calculation point. There are some special properties, an inclination angle, viewing angles from a start to an end angle and a step width. The inclination angle defines the observer’s viewing direction towards the horizontal. Start and end angle defines the observer’s vertical viewing section. Here 0° is the direction along the positive X-axis, positive angles move counter clockwise. Step width defines the different viewing directions between the start and end angle.
GR observers can easily be placed as a line or even as a field by using the function “Copy along a line”.

So to sum up, the UGR value is only for interior rooms specified and the GR for exterior scenes. If you would like to plan an interior scene in DIALux 4, you have to work with the UGR calculation.

Best regards,
DIAL Support Team


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