Important noted：Glare is one of the most common problems in lamps, among which the glare of led track lighting is the most representative. A lot of designers don’t know how to avoid glare of lamps and lanterns, or how to choose the right anti-glare lamps and lanterns.

Today I’m going to teach you five ways to deal with glare. Before we get started, let’s take a look at the conditions under which the human eye will feel “glare” and what kind of lamps are anti-glare.

Figure: the normal attention range of human eyes is from 30° above to 60° below, in this range, there is dazzling light, which is glare.

Figure: as long as the light emitted by the lamp is controlled within the intercept Angle of >30°, it can be said that this lamp is anti-glare.

So, how should solve the problem of glare of lamps? Come on! Learn these 6 ways to dazzle without a trace.

Shading Angle >30 degrees

The shading Angle of conventional lamps is 30 degrees according to the normal visual Angle of the person, when the shading Angle of lamps is greater than 30 degrees, it can avoid direct light into the human eye. 

1.    Increase the mounting height of the light source

Deep illuminative luminaire is below the circumstance that other structure is invariable, increase the installation height of illuminant, in order to achieve the purpose that increases shading Angle. 

2.    Conventional lamps + Cross anti – glare lamp Angle

Cross anti – dazzle grid is mainly to block the light in both directions.Adjust the critical position of glare from the boundary to the center of the lamp, and then increase the shading Angle to achieve the purpose of anti-glare. 

3.    Conventional lamps + Honeycomb anti-dazzle

Honeycomb anti-dazzle mesh can block the light from all directions, which is the best anti-dazzle effect among all anti-dazzle accessories, and the shading Angle can be close to 90°.It’s also the biggest loss of light. 

4.    Conventional lamps + Shading leaf

Shading leaf can block all directions, easy to lamplight shape, can form from the shading Angle of lamps and lanterns themselves to completely block the light effect, it is the most flexible anti-dazzle accessories, is also the most dazzling appearance plus factor.

Because this accessories is bigger, It can commonly use cooperate with LED track lighting , prevent dazzle at the same time, promote decorate integral figure.

5.     Soft light glass

Soft glass, including ground glass, cloth grain glass, cloth grain + ground glass, can reduce the brightness of the light source surface to a certain extent, and achieve the effect of anti-dazzle to a certain extent.

TESTING IES can provide the parameters of glare. The international standard for UGR is less than 19.

　　Test Report of led lighting sinolumi led limited

　　Abstract：This paper discusses the glare and its evaluation in lighting engineering, as well as the methods to reduce glare and improve lighting comfort.

　　keywords：Glare; Lighting quality; Threshold increment; Light screen brightness; Glare value

　　Glare and It’s Evaluation Method for Lighting Engineering

　　Vincent Ku

　　(Sinolumi led Limited, SHENZHEN 201503)

　　Cathy Yu

　　The paper mainly deals with glare and it’s evaluation for lighting engineering, the methods to reduce glare and increase the comfort of lighting.

　　Keywords: glare; lighting quality; threshold increment; veiling luminance; glare evaluation value.

　　1 The introduction

Excellent lighting design and advanced lighting equipment make us enjoy the comfort and convenience brought by lighting. But glare is always a big headache.

What is glare? Why the glare? How do you reduce or even eliminate glare?      Glare: visual phenomenon in which the distribution or range of brightness in the field of vision is inappropriate, or there is extreme contrast, causing an uncomfortable sensation or reducing the ability to see details or objects.

　   Glare is a bad visual phenomenon, which can make people feel dazzling, causing eye pain, tears, reduced vision, and even temporary loss of visual ability.

       The mechanism by which glare reduces visual function can be understood as follows: the light from the glare source scatters in the direction of the retina, forming a bright light curtain that superimposes on the clear image of the scene. This screen has an equivalent screen brightness, which is equivalent to increasing the background brightness and decreasing the contrast, resulting in glare and difficulty in seeing the target.

Figure 1 human eye and glare

　　2 Definition of a noun related to glare

　　(1) visual field：

　　When the eyes focus on a target, objects in a certain space beyond the fixation point can also be seen, and this space range is called field of vision. The visual field is divided into horizontal visual field and vertical visual field, reflecting the visual range of human eyes in horizontal direction and vertical direction.

　　Static binocular horizontal field of vision up to 160 degrees, vertical field of vision up to 50 degrees. In moving vehicles, the size of the driver’s visual field is related to the speed. The faster the speed, the farther the attention point, the smaller the field of vision, the surrounding scenery is difficult to see clearly.

Research on traffic psychology shows that the vehicle speed is 40km/h and the horizon is 100 degrees. The vehicle speed is 70km/h, and the horizon is 65 degrees. The vehicle speed is 100km/h and the horizon is 40 degrees. Vertical moving field of view, that is, the visual perception space of the driver’s line of sight in the vertical direction, is usually 30 degrees.

　　Due to the influence of eye parallax and poor lighting conditions, the correct color discrimination ability of human eyes in dark environment is very poor. Visual resolution, therefore, depends on the difference in brightness between the object and its background. An object can only be seen if it has a certain brightness contrast.

　　(2) luminance contrast：

　　C=⊿L/Lb =∣Lo-Lb∣/Lb

　　In the formula，⊿L——Identify the difference between object brightness and background brightness;

　　Lo——Identify object brightness (cd/m2);

　　Lb——Background brightness (cd/m2)。

　　Brightness contrast can be divided into “positive contrast” and “negative contrast”. Positive contrast occurs when the object brightness is higher than the background brightness. Negative contrast occurs when the object brightness is lower than the background brightness.

　　(3) threshold contrast：

　　Ct = ⊿Lt /Lb

　　In the formula，⊿Lt——Critical brightness difference, the brightness difference between the target and the background when the human eye can just recognize the target。

　　(4) Visibility Level：

　　The ratio of the actual brightness contrast C of the target and background to the critical contrast Ct。

　　VL=C/Ct=⊿L /⊿Lt

　　Glare can be divided into discomfort glare and disability glare according to the influence degree。

　　(5) discomfort glare：

　　Glare that causes discomfort to the eyes in the field of vision, but does not necessarily reduce the visibility of the visual object. This glare is also known as mental glare。

　　(6) disability glare：

　　disability glare is in the field of vision to reduce the visual function of the glare. It is a glare that reduces the visibility of a visual object, but does not necessarily create an uncomfortable feeling。

　　According to its formation mechanism, glare can be divided into direct glare, disturbance glare, reflection glare and comparison glare。

　　(7) direct glare：

　　Glare produced by luminaries present in the field of vision, especially near the direction of sight。

　　(8) disturbance glare：

　　Glare caused by a luminous object in the direction of a non-viewing object。

　　(9) reflection glare：

　　Glare caused by reflection in the field of vision, especially when the reflected image is seen close to the line of sight。

　　(10) comparison glare：

　　Glare from excessive brightness contrast exists in the light environment。

　　3 Evaluation method of glare

　　So far, the following four main glare evaluation expressions have been summarized for indoor environment, stadium, motor vehicle road and other lighting occasions：

　　3.1 Unified glare rating

　　unified glare rating（UGR）calculate：

　　In the formula，Lb——Background brightness (cd/m2);

　　La——The brightness of each luminaries in the direction of the observer (cd/m2);

　　ω——The solid Angle formed by the luminescent portion of each luminaire to the observer’s eye (sr);

　　P——Position index of each individual luminaries。

　　The above parameters shall be determined according to the following formulas and regulations：

　　1) Lb=Ei /π

　　In the formula，Ei——Indirect illumination in the direction of the observer’s eyes (Lx)。

　　2) La =Ia/A·cosα

　　In the formula，Ia——Luminaries intensity in the direction of the observer’s eye (cd);

　　A·cosα——The projected area of the luminaries in the direction of the observer’s eye (m2);

　　α——The Angle between the normal on the luminaries surface and the direction of the observer’s eye (°)。

　　3) ω=AP /r2

　　In the formula，AP——The apparent area of a luminescent part in the direction of the observer’s eye (m2);

　　r ——The distance between the center of the luminescent component of a luminaries and the eye of the observer (m)。

　　4) The position index P shall be determined by the position index table as the ratio of H/R and T/R generated in FIG. 2。

Figure2: Position exponential coordinates at the origin of the observer position

　　System(R，T，H)，The ratio of H/R to T/R is generated for the center of the luminaries。

　　Application conditions of uniform glare UGR：

　　(1) UGR is suitable for the general lighting device design of simple cubic room, not for the room with indirect lighting and luminous ceiling;

　　(2) It is suitable for the case where the solid Angle formed by the luminaries to the eye is 0.1sr> ohm >0.0003sr;

　　(3) The same kind of lamps and lanterns are evenly spaced;

　　(4) Lamps and lanterns for double – symmetrical light distribution;

　　(5) The eye height of the sitting observer is usually 1.2m, while that of the standing observer is 1.5m;

　　(6) The observation position is generally at the midpoint of the longitudinal and transverse walls, with the line of sight facing forward;

　　(7) The surface of the room is a working face approximately 0.75m above the ground, the light installation surface and the wall between the two surfaces。

　　3.2 glare rating

　　Calculate of Glare value of outdoor sports field (glare rating)GR：

　　In the formula，Lv1——The luminosity of a light curtain produced by a luminaries directed at the eye (cd/m2);

　　Lve——The brightness of a light curtain caused by ambient light that is directly incident to the eye (cd/m2)。

　　In the formula , Each parameter shall be determined according to the following formula：

1)

　　In the formula，Eeyei——The illuminance on the observer’s eye, which is the luminance generated by I light sources on the vertical plane of the line of sight (Lx);

　　θi——The Angle between the observer’s line of sight and the direction in which I light sources are incident on the eye (°);

　　n——The total number of light sources。

　　2) Lve =0.035Lav

　　In the formula，Lav——Visible average brightness of horizontal exposure field (cd/m2)。

　　Lav =Ehorav · ρ/πΩ0

　　In the formula， Ehorav——Average level of illumination on the site (Lx);

　　ρ——The reflectance ratio of an area in diffuse reflection;

　　Ω0——One solid Angle (sr)。

　　Application conditions of glare value GR：

　　(1) The calculation method is used for various lighting patterns of outdoor sports venues under common conditions which meet the uniformity of illumination;

　　(2) Used for line of sight direction below eye height;

　　(3) The background is the field being photographed;

　　(4) The observer position used for calculating glare value can be the grid position used for calculating luminance, or the standard observer position;

　　(5) Can be spaced at a certain number of angles (5°…45°) rotate to select a certain number of observation directions.

GR value corresponds to uncomfortable glare degree：

　　3.3 Increment of threshold value of road lighting glare evaluation TI

　　Threshold increment is a measure of disability glare. Represents the percentage increase in the brightness contrast between the object and its background in order to see the object equally。

　　Threshold increment refers to the average road surface brightness as background brightness. When the background brightness range is 0.05 CD /m2< Lb <5cd/m2, the calculation formula of TI is approximately：

　　TI=65Lv/Lav0.8(%)

　　In the formula，TI—The threshold value increment (%);

　　Lv—Equivalent screen brightness (cd/m2), Assume that the observer is always looking straight ahead of the road axis at an Angle of 1° from the horizontal line (i.e., at a point on the road approximately 86 meters in front of it);

　　Lav—Average pavement brightness (cd/m2)。

　　The formula of Lv of equivalent screen brightness：

　　Lv=10∑(Eeyei/θi2)

　　In the formula，Eeyei—The vertical illumination of the ith lamp to the observer’s eye (Lx);

　　θi—The Angle between the luminous center of the ith lamp and the line of sight of the observer (°)。(1.5°< θ <60°)

　　Threshold increment TI can also be directly measured by a dedicated imaging luminance meter。

　　Table 1 relationship between TI and Lv and Lav  unit：%

　　The average surface brightness Lav of high-grade roads is usually 1.0~2.0 CD /m2, and the threshold increment TI is required to be below 10%. Therefore, when Lav is 1.0 CD /m2, the equivalent light screen brightness Lv should not be greater than 0.15 CD /m2.When Lav is 1.5cd/m2, the equivalent screen brightness Lv should not be greater than 0.20 CD /m2.When Lav is 2.0 CD /m2, the equivalent screen brightness Lv should not be greater than 0.25 CD /m2。

　　Lv is the sum of 10Eeye/ theta 2 of all lamps with an Angle of 1.5 degrees to 60 degrees from the viewing target. In the light fixture arrangement, that is, with all theta angles, the smaller the better。

　　3.4 Glare control levels in road lighting, G

　　The uncomfortable glare experienced by drivers in road lighting can be measured by the glare control level G.G value and the nature of the lamp itself and layout。

　　Factors affecting glare control grade G include：

　　(1) Lamps and lanterns and light sources：

　　1) In the c-gamma system, C=0 and gamma =80° absolute light intensity, that is, the light intensity in the direction of 80° from the lowest point of the lamp in the vertical plane parallel to the road axis，the I80。

　　2) The ratio of absolute light intensity in the direction of C=0 and gamma =80° to that in the direction of C=0 and gamma =88°，the I80/I88。

　　3) The luminescent area of a luminaries as seen from 76° perpendicular to the right side of the luminaries，The F。

　　4) The color coefficient of the light source used is expressed in C.When the light source is low pressure sodium，C=0.4; High pressure sodium lamp，C=0.1; High pressure mercury lamp，C=-0.1; Other light sources，C=0。

　　(2) Facility layout：

　　1) Average road brightness，The Lav。

　　2) Horizontal line of sight (1.5m) from the height of the luminaries，The h’。

　　3) Number of lamps per kilometer，The p。

　　The relationship between these parameters and the glare control level G is as follows：

　　G=13.84-3.31logI80+1.3(log(I80/I88))1/2-0.08log(I80/I88)+1.29logF

　　+0.97logLav+4.4logh’-1.46logp+C

　　It should be noted that the parameters in the above equation only apply to the following range：

　　50cd≤I80≤7000cd;

　　1≤I80/I88≤50;

　　0.007m2≤F≤0.4m2;

　　0.3cd/m2≤Lav≤7cd/m2;

　　5m≤h’≤20m;

　　20≤p≤100。

　　

　　4 Glare control strategy

　　The direction of glare control strategy can be summarized from the above evaluation formulas：

　　(1) Improves background brightness in the field, because glare is normally inversely proportional to background brightness. But it should be achieved by improving the lighting efficiency of the system, rather than simply increasing the power consumption。

　　(2) Reduce the vertical illumination produced by the lamp in the observer’s eye, thereby reducing the equivalent light screen brightness produced by the glare source in the observer’s eye。

　　(3) As far as possible to see the target and luminescent surface of the included Angle increased. This involves the reasonable arrangement of lamps and lanterns。

　　(4) Reduce the luminance of the luminaries surface。

　　(5) Set up scientific light interception facilities。

　　5 The end

　　In most cases, glare will have a negative impact on the lighting effect, or even directly lead to the failure of lighting design. Our goal is to seek a scheme that can reasonably restrain glare, efficiently utilize the luminous flux of light source and improve the efficiency of energy utilization. Therefore, scientific lighting design is very important