presents a led bar. It needs 24 V DC power for the 12 leds that are used. This led bar has on both ends a connector for the lampvoltage. Herewith a number of led bars can be connected in series. 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	4256 K	Neutral white
Luminous intensity Iv	4008 Cd
Beam angle	25 deg
Power P	26.2 W
Power Factor	1.0	For every 1 kWh net power consumed, there has been 0.0 kVAhr for reactive power. Note that a 24 V DC power was used, therefore the power factor equals 1.
Luminous flux	928 lm
Luminous efficacy	35 lm/W
CRI_Ra	71	Color Rendering Index.
Coordinates chromaticity diagram	x=0.3732 and y=0.3848
Fitting	24VDC	This is a DC voltage.
L x W x H external dimensions	1010 x 55 x 25 mm	External dimensions of the led bar.
L x W luminous area	987 x 31 mm	Dimensions of the luminous area (used in Eulumdat file). This is equal to the size of the opening of the glass on top of the led bar. Through this glass the leds output their light.
form factor	bar
General remarks		The ambient temperature during the whole set of measurements was 26-26.5 deg C.Warm up effect: A strange effect ocurred during warmup: after 30 minutes the power consumed dropped, as well as the illuminance and the color temperature. Not counting this effect, then the illuminance decreases with 13%. Voltage dependency: the illuminance and power consumption are almost independent on the voltage. Except when the voltage drops below 21 V. A photo of the led-lense is added.
Measurement report (PDF)
Eulumdat file		Right click on icon and save the file.

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. The C0-C180 plane is along the length of the led bar and the C90-C270 is perpendicular to that. The bundle is very small (focused). There is a little drop of light level at 0 degrees (straight underneath the led bar).

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 are little 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 25 degrees.

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 928 lm.

Luminous efficacy

The luminous flux being 928 lm, and the power of the lightbulb being 26.2 W, yields a luminous efficacy of 35 lm/W.

A power factor of 1 (since DC voltage is used) means that for every 1 kWh net power consumed, a reactive component of 0.0 kVAr was needed.

Light bulb voltage	24 VDC
Light bulb current	1.09 A
Power P	26.2 W
Apparent power S	26.2 VA
Power factor	1.0

Color temperature and Spectral power distribution

The spectral power distribution of this light bulb.

The measured color temperature is about 4250 K which is neutral white.

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.

The color temperature is given for inclination angles up to 30 degrees, since at higher angles there is almost no light output anymore.

The value remains constant within 7 %.

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 small distance from the Planckian Locus (the black path in the graph).

Its coordinates are x=0.3732 and y=0.3848.

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 71 is lower than 80 which is considered a minimum value for indoor usage.

Note: the chromaticity difference is 0.0059 indicates the distance to the Planckian Locus. Its value is  higher than 0.0054, which means that the calculated CRI result is not 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 lamp parameters measured: illuminance E_v [lx], the lamppower P [W] and the luminous efficacy [lm/W].

Lamp voltage dependencies of certain light bulb parameters, where the value at 24 V is taken as 100 %.

The consumed power and the illuminance vary insignificantly when the voltage varies between 21-26 V. It drops sharply below the 21 V.

When the voltage at 24 V varies with + and – 1 V, then the illuminance doesn’t vary at all, 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.

There is a sudden drop in values, after 33 minutes of warmup time. This is not understood.

Note that the voltage unit, converting the mains voltage from 230 V AC into 24 V DC, is included in this measurement. The readings for the illumination are significant and come from the led bar only. The readings for the power are the sum of the voltage unit and the led bar, so these values need not be considered.

The illumination decreases with 13 % (when the drop effect is excluded).

Additional photo

The led lense which is clear.