Understanding UGR calculation by EVO

questions regarding the handling of DIALux evo. (features, tools, options, settings)
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Joined: Tue Oct 02, 2012 3:02 pm

Understanding UGR calculation by EVO

Post by kikeblackberry » Sat Nov 04, 2017 3:14 pm


I ask your support in order to understand how EVO calculate UGR.

I have read this article: https://www.dial.de/en/blog/article/no- ... gr-method/. At the end of the second paragraph it can be read “Where there are lighting installations with luminaires from which 65% of the light is emitted indirectly and where narrow beam spots or asymmetrically radiating luminaires are installed, then, by definition, it is not possible to indicate a UGR value.”.

I created a single project and then inserted several LED linear luminaire (1200x200mm - obviously its light distribution is not symmetrical) at not uniform grid (Not positioned symmetrically into the room), then I inserted a calculation surface and I configured it as UGR calculation surface. After that I ran EVO and it calculated the UGR value.

I opened the Product Data Sheet on EVO Documentation and this message was show “It is not possible to generate a UGR diagram, as the light distribution is asymmetrical”. This message agrees with CIE 117-1995 due to LDC of luminaire.

So, how can I understand results calculate by EVO if luminaire’s LDC are not symmetrical nor equaled spaced?
What kind of assumptions should be taken into account in order to get a good calculation results on EVO according with CIE 117 or related standards?

Besides CIE 117, is it EVO taking into account CIE 190, CIE 146 and CIE 147 for UGR calculations?

I really appreciated your answer.

Best regards

Posts: 1185
Joined: Wed Mar 07, 2012 3:07 pm

Re: Understanding UGR calculation by EVO

Post by Csuleiman » Mon Nov 06, 2017 12:52 pm

Dear kikeblackberry,

DIALux is handling the UGR calculations exactly according to the CIE document 117, discomfort glare in interior lighting.

The UGR values can be calculated according to a formula given in this document. This is the way it is done for the UGR calculation grid and for the UGR calculation points.
Please download the document by using the following link: https://b2b.dial.de/index.php/s/V54FLfmPRYSVpkX

The UGR table is calculated on a very specific situation described in the standard. There are a lot of restrictions and definitions to be taken into account, if you want to calculate a table.

Definitions, limitations and parameters that have always to be taken into account:

- No UGR in exterior lighting
- No UGR in Road lighting
- You can calculate UGR, but it makes no sense if you have luminaries with an indirect light output ratio above 65%
- Calculation can only be done for luminaries in the field of view above 90° viewing angle
- Calculation can only be done for luminaries within the positions defined for the “position index by Guth”

Definitions, limitations and parameters that have to be taken into account for the table:

- Only one type of luminaries
- Only rotational or two axis symmetric luminaires
- Only rectangular room
- No obstruction
- Fixed spacing (spacing to height ratio either 0.25 or 1)

If a client asks for the UGR value, he normally does it because of the EN12464 Lighting of workplaces – indoor workplaces. It is stated in this standard (chapter 4.4.1.), that the values from the table method should be used. If a table can’t be calculated, that’s it. It is not defined in this case. That means UGR does not make sense. You could use an UGR calculation grid or an UGR calculation point but that’s not what the client ask for.

- Do not provide UGR calculations or tables for exterior luminaries, it makes no sense
- If you have an interior luminaire and it should be symmetrical (either rotational or two axis) the LDC you put into the database should be symmetrized (No software can recognize that, it has to be done by the photometric lab)
- Yes the UGR calculation (surface or point) is depending on the observers position and viewing direction
- If you want to know UGR in all directions you need a lot of points/surfaces
- 1.2m is the standard height for a sitting observer

The CIE 117 gives the user the freedom to choose. The CIE S 008 (content largely identical to EN12464-1) defines the SHR = 1. Nevertheless most manufacturers and planners in Europe use the SHR = 0.25. This is also more "critical" as SHR = 1.
The LiTG publication for UGR method used mostly the SHR 0.25.

CIE 190: 2010 is also based on the definition of the UGR method according to CIE 117. This is also explicitly mentioned as a definition of this method. In the CIE 117, the UGR method was described, but some parameters were imprecise, or rather, selectable by the user.

These include:
- The method to be used to calculate the background luminance. Here many methods compete, e.g. LitG 3.5, NB, TM, CIE ...
- Spacing to Height Ratio (SHR) to be used. = 0.25 or 1.0
- Corrected or uncorrected UGR table. Based on 1000lm or actual luminous flux
- …

In DIALux, we have sought and found a consensus solution with many partners who were also involved in the standardization process (EN and CIE). It was important not to make the user unsure of the same luminaire by using different tables.

Unfortunately, this has not always been possible. This allows the users in DIALux to select whether the SHR should be 0.25 or 1.0. Since the continental Europeans preferred the SHR = 0.25 and the colleagues from the UK the SHR = 1, a setting option was necessary.

Regarding other parameters, agreement has been possible.

In CIE 190: 2010, but no current standardization for indoor lighting (e.g. EN12464 or ASR), some parameters are now defined. Basically this is to be welcomed, but unfortunately the lack of referencing here is disadvantageous.

In CIE 190, you can now find UGR tables which are not corrected. This is understandable but not meaningful.
- For classical luminaires the correct luminous flux of the lamps must be corrected
- With LED lights, a standardization to 1000lm makes no sense at all
The correction is made via UGR(Φ) = UGR(Φ0) + 8log (Φ/Φ0)

Thus, in the case of uncorrected tables, the planner must multiply each UGR value of the table by this factor in order to reach the planning value of this system in this room. In our opinion, a superfluous and not understandable matter for many planners.

DIALux takes the planner's work, simplifies the process, and displays the corrected values in the UGR table.

The CIE 190 refers to the ISO 8995: 2002 / CIE S 008. This document is APPROXIMATELY in line with EN 12464. APPROXIMATELY means that (here comes my personal opinion to the statement) the men present in the committee from the UK, who prefer the SHR = 1 application, have inserted these into the ISO / CIE S 008. The UGR method is based on research leading to the British GR. The GR values were however determined with SHR 1:1. In order not to have to present completely different values to the UK market, the UK colleagues insisted on the SHR = 1 application. Either way, an agreement EU far would have been better, of course.

The fact is:
- The CIE 117 and the EN12464 referencing it leave freedom of choice in the selection of the SHR, the continental Europeans prefer 0.25
- The CIE 190 and ISO 8995 / CIE S 008 write SHR = 1.0. This is also disputed.

Our conclusion:

CIE 190 is an attempt to improve the CIE 117 with respect to the adjustment of the frame parameters. However, since the CIE 190 is not referenced (e.g. from EN12464) and some approaches (e.g. uncorrected UGR values) are rather fault-prone and unintelligible, DIALux continues to output the corrected UGR values with adjustable SHR. This is not wrong and serves the planner. To our knowledge, this approach is by mutual agreement with all (almost) manufacturers in the EU area.

Best regards,
DIAL Support Team


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