presents a recessed high performance led down lighter, under the name of Meson. It has 4 x 8 leds in it. This article shows the measurement results. Many parameters are also found in the Eulumdat file.

See this overview for a comparison with other light bulbs.

Summary measurement data

parameter	meas. result	remark
Color temperature	3229 K	Warm white
Luminous intensity Iv	313 Cd
Beam angle	86 deg
Power P	19.5 W
Power Factor	0.95	For every 1 kWh net power consumed, there has been 0.3 kVAhr for reactive power..
Luminous flux	628 Lm
Luminous efficacy	32 Lm/W
CRI_Ra	85	Color Rendering Index.
Coordinates chromaticity diagram	x=0.4163 and y=0.3879
Fitting	230V	It uses a current source for the leds, converting 230 V mains into current.
PAR-value	2.7 μMol/s/m2	The number of photons seen by an average plant when it is lit by the light of this light bulb. Value valid at 1 m distance from light bulb.
S/P ratio	1.4	This factor indicates the amount of times more efficient the light of this light bulb is perceived under scotopic circumstances (ow environmental light level).
W x L  x H external dimensions	120 x 120 x 66 mm	External dimensions of the light bulb.
W x L luminous area	92 x 92 mm	Dimensions of the luminous area (used in Eulumdat file). This is equal to the width and length of the frosted transparent plate at the front side.
General remarks		The ambient temperature during the whole set of measurements was 23-24 deg C. The maximum body temperature was 25 deg warmer than ambient. Warm up effect: during the warm up time the illuminance decreased with 12 % and the color temperature increased with 4 %. Voltage dependency: the power consumption and illuminance do not vary when the voltage is varied from 200 – 250 V. This article contains an additional photo of the leds inside this light bulb.
Measurement report (PDF)	tbc
Eulumdat file		Right click on icon and save the file.

Overview table

The illuminance values are measured in the far field (i.e. at least 5 times the distance of the largest illumination dimension) such that the light bulb can be seen as a point source. From this distance the values are calculated to values at the given distances.

If the light is not anymore a point source at any given distance, then the real measured values (with an actual lux meter) will be lower than indicated in this table.

In general, the light source is not anymore a point source starting from distances lesss than 5x the length of the luminous area.

Eulumdat light diagram

An interesting graph is the light diagram, indicating the intensity in the C0-C180 and the C90-C270 plane. This light diagram below comes from the program Qlumedit, that extracts these diagrams from an Eulumdat file.

The light diagram giving the radiation pattern.

It indicates the luminous intensity around the light bulb. This light bulb has the same light diagram for the C0-C180 as for the C90-C270 plane since it has symmetry over 90 degrees (it is a square).

The unit is Cd/1000lm, meaning the intensity in Cd assuming there would be 1000 lumen in the measured light bulb. This enables comparing different types of light bulbs.

Illuminance Ev at 1 m distance, or luminous intensity Iv

Herewith the plot of the averaged luminous intensity Iv as a function of the inclination angle with the light bulb.

The radiation pattern of the light bulb.

This radiation pattern is the average of the light output of the light diagram given earlier. Also, in this graph the luminous intensity is given in Cd.

These averaged values are used (later) to compute the lumen output.

Intensity data of every measured turn angle at each inclination angle.

This plot shows per inclination angle the intensity measurement results for each turn angle at that inclination angle. There normally are differences in illuminance values for different turn angles. However for further calculations the averaged values will be used.

When using the average values per inclination angle, the beam angle can be computed, being 86 degrees. This is the average value but as the light bulb has a symmetry over 90 degrees, this angle is valid for most turn-angles the light bulb is looked at.

Luminous flux

With the averaged illuminance data at 1 m distance, taken from the graph showing the averaged radiation pattern, it is possible to compute the luminous flux.

The result of this computation for this light spot is a luminous flux of 628 Lm.

Luminous efficacy

The luminous flux being 628 Lm, and the power of the light bulb being 19.5 W, yields a luminous efficacy of 32 Lm/W.

A power factor of 0.95 means that for every 1 kWh net power consumed, a reactive component of 0.3 kVAr was needed.

Light bulb voltage (used on power supply!)	230 VAC
Light bulb current	89 mA
Power P	19.5 W
Apparent power S	20.5 VA
Power factor	0.95

Of this light bulb the voltage across ad the resulting current through it+its constant current driver power supply are measured and graphed.

Voltage across and current through the lightbulb

A very very nice sine form of the current. A very good job of the current driver. There is a little phase shift, that results in a power factor value a little less than 1.

Also the power spectrum of the current is determined.

Current power spectrum in % of the first harmonic (50 Hz).

With such a nice sine form of the current there are hardly any higher harmonics.

Color temperature and Spectral power distribution

The spectral power distribution of this light bulb, energies on y-axis valid at 1 m distance.

The measured color temperature is about 3225 K which is warm white. Besides the blue led (peak at 450 nm) with yellow phosphorus (resulting in a bump at 560 nm), there is also a red led used (see the peak at 630 nm).

This color temperature is measured straight underneath the light bulb. Below a graph showing the color temperature for different inclination angles.

Color temperature as a function of inclination angle.

Measured is in the angles 15 and 195 degrees, and the measurement of CCT has been stopped when less than 5 lux (low illumination value) were measured or when the inclination angle was 90 degrees. With this lamp at 85 degree inclination angle less than 5 lux was measured (at the specific measurement distance).

The maximum beam angle is 86 degrees, meaning at an inclination angle of 43 degrees there is 50 % left of the initial illuminance value at 0 degrees. Most of the light energy is within this area. In this area the color temperature stays within 2 % of its value at 0 degrees inclination angle.

PAR value and PAR spectrum

To make a statement how well the light of this light bulb is for growing plants, the PAR-area needs to be determined. PAR stands for Photosynthetic Active Radiation which is that radiation that participates actively to photosynthesis and is expressed in μMol/s/m².

Photosynthesis is the essence for growth and flowering of plants, where the blue part of the light spectrum is responsible for growth and the red part is responsible for flowering and budding (for gemmation). For photosynthesis it is more important to count the number of photons rather than the power in the light.

The power spectrum (power per wave length) of the light of the light bulb is converted into the number of photons (number of photons per wave length) and then these number of photons is weighted against the relative sensitivity of an average plant (which varies in value dependent on the wave length). The relative sensitivity curve in DIN-norm 5031-10:2000 is used for this. The next image shows the result.

The photon spectrum, then the sensitivity curve and as result the final PAR spectrum of the light of this light bulb

The black curve gives the power spectrum of the light of this light bulb, in number of photons per wave length.

In red the relative sensitivity curve of an average plant (according to DIN norm 5031-10:2000).

Multiplying these two results in a curve showing the number of photos per wave length of the light of this light bulb, the PAR spectrum.

Summing all the photons, gives a PAR number that for this light results in 2.7 μMol/s/m². This value is valid at 1 m distance from the light bulb.

Dividing the PAR number by the total number of photons of the light of this light bulb gives a sort of PAR efficiency, which is 63 % (valid for the PAR wave length range of 400 – 725 nm). So maximally 63 % of the total of photons in the light is effectively used by the average plant (since the plant might not take 100 % of the photons at the frequency where its relative sensitivity is 100 %).

Note: when mentioning this percentage of efficiency, it is important to verify if all wavelengths are present in a sufficient manner. Not that only blue light is available, when the plant is going to be used for flowering where specifically red light is needed.

S/P ratio

The human eye uses rods and cones. The rods work at scotopic light levels (twilight, night) and the rods at high(er) light levels (daytime, but also close to twilight). Each type of receptor has its own sensitivity for light. The rods are 2.7 times more sensitive than cones, and most for light at a blueish-greenish color whereas compared to the cones’ sensitivity for green light (555 nm).
The S/P ratio gives the maximum difference in sensitivity of the rods at their most sensitive wavelength compared to the cones at their’s. The more blueish (cold white) the light, the more the S/P ratio can be.

The light of this light bulb has a certain spectrum leading to an S/P ratio of 1.4. The light of this lightbulb at scotopic light levels is perceived this factor higher than it would be a photopic light levels.

The power spectrum, sensitivity curves and resulting scotopic and photopic spectra (spectra energy content defined at 1 m distance).

Since there is a lot of red content in the light, the S/P ratio is not so big (rods do not see reds).

More info will come in a separate article.

Chromaticity diagram

The chromaticity space and the position of the lamp’s color coordinates in it.

The light coming from this lamp is at a distance from the Planckian Locus (the black path in the graph).

Its coordinates are x=0.4164 and y=0.3879.

Color Rendering Index (CRI) or also Ra

Herewith the image showing the CRI as well as how well different colors are represented (rendered). The higher the number, the better the resemblance with the color when a black body radiator would have been used (the sun, or an incandescent lamp).

Each color has an index Rx, and the first 8 indexes (R1 .. R8) are averaged to compute the Ra which is equivalent to the CRI.

CRI of the light of this lightbulb.

The value of 85 is higher than 80 which is considered a minimum value for indoor usage.

Note: the chromaticity difference is 0.0035 indicates the distance to the Planckian Locus. Its value is lower than 0.0054, which means that the calculated CRI result is meaningful.

Voltage dependency

The dependency of a number of lamp parameters on the lamp voltage is determined. For this, the lamp voltage has been varied and its effect on the following light bulb parameters measured: illuminance E_v [lx], the lamppower P [W], the (Correlated) Color Temperature [K] and the luminous efficacy [Lm/W].

Lamp voltage dependencies of certain light bulb parameters, where the value at 230 V is taken as 100 %.

The consumed power varies < 2 % and the illuminane doesn’t vary when the voltage varies between 200-250 V. This variation is insignificant.

When the voltage at 230 V varies with + and – 5 V, then the illuminance varies within 0.1 %, so when abrupt voltage changes occur this effect is not visible in the illuminance output.

Warm up effects

After switch on of a cold lamp, the effect of heating up of the lamp is measured on illuminance E_v [lx], color temperature CT or correlated color temperature CCT [K], the lamppower P [W] and the luminous efficacy [lm/W].

Effect of warming up on different light bulb parameters. At top the 100 % level is put at begin, and at bottom at the end.

The warm-up time is about 1 hour, during which the illumination drops 12 %, the consumed power doesn’t change significantly and the color temperature increases with 4 %.

Additional photo

The LEDs from close,on their heatsink.

It is well seen that per 8 leds two red leds are used and surrounded by 6 blue leds with yellow phosphorus. The addition of red helps a lot in getting a high CRI value.