A fundamental parameter for assessing the quality of LEDs is the index MacAdam that is useful for identifying the color constancy.
In the early 1940s, David L. MacAdam performed an empirical experiment to define the sensitivity of the human eye to the color.
The result was the definition of ellipses to describe the color distances on the XY coordinates of the chromatic scale. The area enclosed by each ellipse includes all the colors identical to the standard reference color, the size of the ellipse is given in SDMC (Standard Deviation of Color Matching) and is evaluated on a 7-point scale.
The new European standard for lighting of indoor workplaces came into force in August 2011. The main differences:
The worktop reflectance factor is no longer compulsory. However a specific note states that the reflectance factor of the main objects (furniture, machinery, desk surface, etc.) should range between 0.2 and 0.7.
Directive 2009/125/EC of the European Parliament and of the Council of 21 October 2009 establishing a framework for the setting of ecodesign requirements for Energy-related Products (ErP).
In particular the regulation establishes ecodesign requirements for placing on the market the general lighting electrical products that are directional lamps, light emitting diode lamps and related equipment.
Following the regulations, ESSE-CI start labeling all the products with icon of ErP classes in the present catalogue.
Thanks to professional design ability, state-of-the-art technologies used and quality control, Esse-ci’s LED products reach a perfect balance between lumen per watt and lumen per cost.
All the LED products belong to the Class A, A+ and A++ of ErP.
Following the label for LED products.
The light flow is the amount of light given off by a light source in an arc of time. The unit of measure is a lumen (lm). From the relationship of the light flow and the power used (W), the lighting efficiency is established, which is a fundamental indicator in establishing energy savings. The following table shows some fundamental data for the main types of lamps on sale.
|LAMP||COL. TEMP.||RA||EFFICIENCY (lm/W)||LIFE (h)|
|Compact Fluorescent 55W||3000K||93||87||12000|
|Linear Fluorescent T8 36W||4000K||85||93||12000|
|Linear Fluorescent T8 36W||4000K||85||104||20000|
|High intensity discharge WDL 150W||3000K||85||95||9000|
|High intensity discharge NAV-T 250WLed||2000K||<25||108||16000|
PHOTOBIOLOGICAL SAFETY OF LEDS
The light sources used to produce light also present related emissions of electromagnetic radiation not perceptible by the human eye, but can induce effects on people or things exposed to the same luminous flux.
Typical examples of newspapers radiation emitted along the light are the heat produced by an incandescent lamp and the tan and discoloration produced by sunlight.
Even the diodes LEDs are not exempt from the production of radiation-related, especially the diodes with high color temperature light and cold (>6500°K).
The intensity of this radiation, mainly UV, grows proportionally to the increase of the “light power” of the LED diode and the possible harm or risk is inversely proportional to the cone within which the light is emitted (beamwidth).
Any risks or photobiological damages are induced by radiation that are at the extremes of the visible range (380-780nm) that is:
Infrared (IR-A, IR-B, IR-C) typically able to produce thermal effects;
Ultraviolet (UV-A, UV-B, UV-C) in a position of producing ionizing effects instead.
These photo-biological effects or damage, created by UV or IR, are charged to the skin, to the underlying tissue (erythema, photo-aging, photo-toxic reactions, skin burns), to the eye and its component parts: crystalline and cornea (cataract, photokeratitis, photoretinitis, scotoma).
It was therefore necessary to adopt a set of procedures that provide for the identification of radiation that produce photobiological effects, to define exposure limits, to define a criterion for measuring radiation above and finally to define risk groups in which the light sources take part.
CLASSIFICATION SIURCES IN GROUPS OF RISK
As a result of the tests performed with the instrumentation and methodology indicated by the standard EN 62471:2008, were identified 4 risk groups:
Exempt group (RG 0)
Risk group 1 (RG 1)
Risk group 2 (RG 1)
Risk group 3 (RG 1)
All the appliance Esse-Ci with LED technology are part of the category RG O cathegory for all the risk groups.
Two fundamental measurements are given by the light flow: illumination and lighting intensity, which should be explained to prevent confusion.
Lighting intensity (I), is expressed in candles (cd), measures the amount of flow in a punctiform light source in a specific direction, no matter what surface or object is being illuminated; illumination however, oriented for technical lighting design and considered by UNI10380 standards, measures the amount of light for unit of surface.
Considering that the set unit of measure is lux (lx) and that normally we refer to a surface area of 1m2, the formula is:
As the lighting source is not punctiform, the concept of luminance has been introduced (L) i.e. the relationship between lighting intensity issued and the issuing surface, expressed in cd/m2.
PROTECTION AGAINST IMPACT WITH EXTERNAL SOLID BODIES
PROTECTION AGAINST LIQUID PENETRATION
The colour temperature of a light source is based on the principle that an incandescent item changes colour as the temperature increases. The theoretic principle this measurement is based on is the “radiating black body”. As the temperature increases, the black body gradually changes from red to orange, to yellow, to white to finally reach white-sky blue.
This measurement is expressed in Kelvin degrees (K). The following diagram shows its trend:
The chromatic yield of light source corresponds to the ability to recognise the colours of an exposed item.
This need varies with the item: generally it is more marked for multi-coloured items and lower in monochrome items.
The chromatic yield indicator (Ra) is a system that has been derived from vision experiments to assess the impact exercised by different light sources on the colour that is perceived of items and surfaces.
First of all the colour temperature of the light source must be identified. Secondly, eight sample colours are lit by the lamp being studied, and the results are compared with those of a “black body” which has been taken to the same colour temperature. If none of the samples change chromatically, the light source is recognised an Ra of 100. As the performance worsens a lower mark is granted. Generally speaking, light sources with an Ra equal or higher than 80 are assigned good chromatic yield properties.
The group of endless segments that trace the lighting intensity of a source in each point of its surface create the so-called photometric solid. The polar diagram represents the distribution of lighting intensity along two main planes: crossway (0° - 180°) and lengthways (90° - 270°). The values are measured in cd/m2.
POLAR GLARE DIAGRAM
This diagram shows the luminance on a polar basis with Cartesian axes 0°-180° and 90°- 270°. It shows the luminance values for angles of 55°, 65° and 75° respect to the vertical. On the basis of standard 12464-1, it is the reference graph for measuring glare.
The quality ratings refer to the internal of the diagram. Curves that are on the lift of the straight line they represent are acceptable.
The 12464-1:2002 standard did not contain any provisions concerning these surfaces whilst the 12464-1:2011 standard establishes that mean illuminance should be:
for walls: > 50 lx with U0 ≥ 0.10
for ceilings: > 30 lx with U0 ≥ 0.10
The reasons for the introduction of this provision are based upon the fact that both walls and ceiling are included in the observer’s field of view (also called background) and are therefore of the utmost importance for the environment visual comfort.
The standard moreover specifies that a lower illuminance level may be accepted should the above-mentioned level not be complied with due to the dimensions and the complexity of the rooms or to operational factors.
For example, poor mean illuminance values are accepted in case of high ceilings with suspended lighting fixtures located far from the ceiling.
For rooms where visual activities or tasks require luminous surfaces, such as offices, schools and hospitals, the mean illuminance values should be 75lux for walls and > 50 lux for ceilings. For both uniformity must be equal to U0 ≥ 0.10.
The definition of the immediate surrounding area remains unchanged: a band of at least 0.5m wide around the task area.
The illuminance values of this area are summed up in the table below:
This parameter was introduced by the 12464-1:2011 standard. The background area consists of a band, at least 3m wide around the immediate surrounding area, and must have a mean illuminance value equal to 1/3 of the latter.
Table 5 shows both the uniformity of the task area and the compulsory illuminance value per each task.
The minimum illuminance uniformity value for immediate surrounding areas is 0.4 whilst for background areas is 0.1.
Unlike 12464-1:2002 standard, 12461-1:2011 standard defines the minimum number of measuring points and the dimensions of the grid cells for the different task areas. Illuminance grids are defined according to UNI EN 12193 standard criteria and have the following characteristics:
The ratio of length to width of the grid cells ranges between 0.5 and 2.
Measuring points correspond to the barycentre of each cell.
The maximum size of a cell is calculated using the following formula:
Where “p” is the grid cell size and can reach a maximum of 10m and “d” is the longer dimension of the area if the ratio of the longer to the shorter side is less than 2, otherwise “d” is the shorter dimension. “n” represents the total number of measuring points along the dimension “d”. It is the closest whole number greater than the ratio:
“p” is the result of the ratio:
The measuring points along the other side of the grid are calculated in the same way.
The ratio of one side to the other must be as close to 1 as possible. Illuminance grids must not include a band, at least 0.5m wide, from the walls unless the visual task is not carried out at a lower distance.
Cylindrical illuminance and modelling are two indexes important for visual comfort.
The cylindrical illuminance is aimed at guaranteeing an optimum luminance of all solid objects, people’s faces in particular.
Therefore an adequate mean cylindrical illuminance value must be guaranteed in all areas where people move.
The mean cylindrical illuminance values must not be lower than 50lx on a plane at a height of 1.2m for seated persons and of 1.6m for standing persons above floor level.
In all rooms where an optimum visual communication is required (e.g. offices, classrooms, meeting rooms), the mean cylindrical illuminance must not be lower than 150lx. Illuminance uniformity must not be lower than 0.1 in both cases.
Modelling instead is the balance between diffuse and directional light. The modelling index is the ratio of cylindrical to horizontal illuminance on the same measuring point of the grid. An adequate modelling value ranges between 0.3 and 0.6 in case of a uniform distribution of the lighting fixtures or of a luminous ceiling.
The negative effects of a poor modelling value can be counterbalanced by daylight. Therefore modelling values not included in the above range may also be accepted.
Cylindrical illuminance is the mean value of vertical illuminance rotating around a certain measuring point.
12464-1:2001 standard states that as far as the lighting equipment maintenance factor is concerned CIE 97:2005 (2nd edition) should be taken into consideration. It is calculated using the following formula:
MF = maintenance factor.
LLMF = % of the physical luminous flux degradation of a lamp.
LSF = lamp survival factor expressed in %, i.e. the number of lamps still functioning after a certain period of time.
LMF = luminaire maintenance factor: % of luminous flux degradation of the luminaire over time.
RSMF = room surface maintenance factor is the % of degradation of light from reflective surfaces of a room over time.
12464-1:2011 standard refers to UNI EN 15193 standard for calculation of energy consumption.
It is an important parameter also in light of the most recent European directives concerning energy saving.
According to 12464-1:2011 standard the maximum luminance values for lighting fixtures that produce veiling reflections on screens (LCD) due to their position must be lower than the values indicated in the table below:
Case A refers to positive polarity flat screens with standard settings for colour and information displayed (e.g. offices, schools, etc.).
Case B refers to negative polarity flat screens and/or screens with high quality features concerning colour settings and details of the information displayed (e.g. CAD, colour inspection).
In case of a high brightness screen used with less than 200 cd m2, provisions concerning medium brightness screens should be followed.
The screen brightness represents the maximum brightness of the white parts of the screen. This value is indicated by the manufacturer. Some activities, visual tasks or technologies using extremely glossy screens might require different light conditions.
12464-1:2011 standard further highlights the importance of light for people’s health and wellbeing. It affects mood, attention and circadian rhythms as well as the psychophysical and psychological states. The recommended variation range has not been decided yet.
|Glare||Condition of discomfort or reduced visual capacity caused by unsuitable distribution or luminance gradient or excessive contrast in space or time.|
|Solid angle||Ω||Angular opening subtended to the centre of a spherical cap of an area that is numerically the same as the square of the radius sr (steradian).|
|Luminance contrast||Relative difference in luminance between two parts of a visual||(L object - L background) /|
|Luminous efficiency||The ratio between the light flow issued by the lamp and the absorbed electric power. It gives the economic level with which the electric power absorbed is transformed into light.||lm / W|
|Maintenance factor||Ratio between average illumination on the worktop after a certain time using the installation and the average illumination given in the same conditions with a new installation.|
|Reflection factor||ρ||Ratio between the reflected light flow and the incident flow at the given conditions.|
|Use factor||U||Ratio between the light flow received from the reference surface and the sum of the individual flows from the installed lamps.|
|Light flow||Φ||Amount of light given into space by a source.||lm (lumen)|
|Illumination||E||At a point on a surface, it is the ratio between a light flow received from a surface and the area of the same surface that is perpendicular to the flow direction.||lx (lux)||The illumination produced from a light flow of 1 lm which falls evenly onto a surface of 1m2 is 1 Ix.|
|Chromatic yield indicator||Ra||Quantity assessment of the level of agreement between the psychophysical colour of an item illuminated by the test light and that of the same item illuminated by a reference light.|
|Light intensity||I||A light source irradiates its light flow in different directions and with variable intensity. The light intensity corresponds to the intensity of light irradiated in a given direction.||cd|
|Luminance||L||Ratio between the light intensity l issued, reflected or transmitted from the surface S in the assigned direction and the apparent area of the same surface.||cd/m2||L = I / S cos a|
|Useful plane||Reference surface defined as the plane where the visual task is usually carried out.|
|Appliance performance||η||The ratio between the lighted flow issued by the appliance and the sum of the issued flows.||The UNI 10380 standard deals with the specifications for interior artificial lighting in details.|
|Luminance source||The lowest luminance level that can provoke a perceivable stimulus.|
|Punctiform source||A source of radiation of negligible dimensions with respect to the distance between the source and the irradiated surface.|
|Proximal colour temperature||Tones of light that correspond to the temperature of a normalised body (Plank radiator).||K (Kelvin degrees)|