A small led light bulb, with 21 leds in a housing equipped with an E27 screw fitting. This light bulb is from Technea Duurzaam, and for sale at De Energie Bespaarshop. The light coming from this light bulb is yellowish white, which gives a cosy atmosphere.

See this overview for a comparison with other lightbulbs.

Summary measurement results

parameter	meas. result	remark
Color temperature	3150 K	Between warm white and birght white. However the color is yellowish, see the explanation at the CRI.
Luminous intensity Iv	163 Cd	Quite bright.
Beam angle	15 deg	A focused beam.
Power P	1.4 W
Power Factor	0.26	For every 1 kWh net power consumed, there has been 3.8 kVAhr for reactive power.
Luminous flux	32 lm
Luminous efficacy	22 lm/W
CRI_Ra	67	Color Rendering Index.
Coordinates chromaticity diagram	x=0.442 and y=0.432
Fitting	E27
Diameter	50 mm	Measured at the widest part of the lightbulb.
Length	52 mm
General remarks		The ambient temperature during the whole set of measurements was 24.5 deg C. Warm up effect: quite observable. Voltage dependency: present. For all raw measurement data follow this link (gogreen_ledlamp_12w_e27_flame.zip). See also photos of the color of the light.

E_v at 1 meter distance, or I_v

Herewith the plot of the average Luminous Intensity (I_v) dependent from the inclination angle with the lamp. Average here means that all Luminous Intensities measured with different turn angles but the same inclination angle, are averaged.

The radiation pattern of the lamp.

This radiation pattern shows a focused beam.

The luminous intensity dependent from the inclination angle, now with all turn angle measurements included.

The luminous intensity I_v is decreasing rapidly, to get to its 50 % value at 7.5 degrees inclination angle. The beam angle of the light from this lightbulb is then 15 degrees.

Looking at the measurement data at inclination angles between 0 and 10 degrees it becomes clear that there are a number of measurement points with different intensity values. These measurements are taken with the same inclination angle, however with a different turn angle. The results differ which indicates that the leds in the bulb are perfectly mechanically aligned.
The plot at the top of this paragraph shows the averaged luminous intensity values per inclination angle, which is used to compute the total luminous flux.

Luminous flux

With the luminous intensity data as a function of the inclination angle, it is possible to compute the luminous flux.

The result of such computation for this lamp is a luminous flux of 32 lm.

Luminous Efficacy

The luminous flux being 32 lm, and the power of the lightbulb being 1.4 W, yields a luminous efficacy of 32 / 1.4 [lm/W] = 22 lm/W.

A power factor of 0.26 means that for every 1 kWh net power consumed, a reactive component of 3.8 kVAr was needed.

Light bulb voltage	230 V
Light bulb current	24 mA
Power P	1.4 W
Apparent power S	5.5 VA
Power factor	0.26

Color Temperature and Spectral Power Distribution

The spectral power distribution of this lamp.

The measured color temperature is about 3150 K, and the light is yellowish.

Chromaticity Diagram

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

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

Its coordinates are x=0.442 and y=0.432.

Color Rendering Index (CRI) or also Ra

Herewith the image showing the CRI as well as how well different colors are represented. 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 67 is lower than 80 which is considered a minimum value for indoor usage. Since this lightbulb’s color temperature is less than 5000 K, it is compared with the light of a black body radiator of te same correlated color temperature. When comparing, this light bulb renders the different test colors not well enough for general indoor use, for instance to read colorful glossy magazines. The light is yellowish, which gives a cosy atmosphere and that is more the suited use of this light bulb.

Note: the chromaticity difference is 0.012 which is higher than 0.0054, which means that the calculated CRI result might not be meaningful. This is because the chromaticity value of this lamp is relatively far away from the Planckian Locus.

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], color temperature CT or correlated color temperature CCT [K], the lamppower P [W] and the luminous efficacy [lm/W].

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

There is a dependency from the applied voltage. And the dependency there is, is also linear with applied lamp voltage. It indicates that the used power converter inside the lamp behaves stable.

To check whether this dependency can lead to visible changes in illuminance for possible grid voltage changes, just check what variations occur when the lamp voltage varies around 230 V + and – 5 V. Then the illuminance varies < 20 % and will not be visible or noticeable.

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.

There is an effect of the warming up on the lamp parameters. After half an hour burning the temperature of the light bulb is stable, and the illuminance is about 15 % lower than at switch on.

Light bulb’s color

Photos below show the color of the light bulb when switched on.