Bedtime Bulb sent me their warm LED bulb for testing.
Manufacturer website: https://bedtimebulb.com/
Store link: https://www.amazon.co.uk/Bedtime-Bulb-Low-Blue-Light-Healthy/dp/B07XWCNCDJ
The main specs by the manufacturer:
-CRI (Ra) 95
–6W power rating
-AC voltage range of 220-240V, also available in 120V
–2200K color temperature
-Dimmable with some dimmers
–25000 hour lifetime
–50000 cycle lifetime
-Indoor use only
–5 year warranty
Measurements were made in a 50cm integrating sphere with an x-rite i1pro spectrometer after the bulbs had warmed up for 1 hour. Intensity (lux at 1 meter, candela) was measured outside the sphere at 50cm.
The bulbs were connected to mains power which at the time of testing was at 229V.
Output at 1 hour is 439 lumens. This is very close to the manufacturer’s spec of 450 lumens. The output is highly dependent on the input voltage though.
Power consumption was measured at 4.9 watts at 239 volts, but at another time 4.3 watts at 223 volts. Efficiency is ok for a very warm and high CRI light source at 90 lumens per watt.
For all practical purposes maximum output is reached immediately. Light output in lumens was plotted over one hour. The output doesn’t sag during warmup, but does vary a lot depending on the AC mains voltage.
That variation in output is visible to the eye. The bulb’s output is also very sensitive to electrical noise.
The CRI data was measured integrated after a 1 hour warm-up in an integrating sphere.
Color rendering is good reaching CRI Ra of 96 and R9 of 76. TM-30-18 fidelity index Rf of 94 and gamut index Rg of 101 are also excellent. Typical LED technology is evident from the minimal blue hump at 450nm, but as the color temperature is very low, there’s no dip at cyan wavelengths. Visually the light is very pleasing with a slight rosy tint to its very warm temperature of 2250K.
The two bulbs I tested were very well matched and should’t have any visual differences when installed in the same space. The manufacturer specifies the LEDs to be matched within MacAdam Ellipse of 1, which is very tight and totally invisible to the human eye.
Load IES TM-30-18 Color Rendition Reports by clicking the thumbnails:
Color temperature and tint
Tint is slightly below the black body line on both bulbs. Remember that when LEDs heat up, their duv value almost always decreases and becomes less green/yellow. This was measured after 1 hour in an integrating sphere.
Tint shift is basically non-existent. Intensity increases ~70% when the light is measured from the side of the bulb, since the LEDs are positioned almost vertically inside the diffuser.
The 100 hertz oscillation shown in the graph doesn’t cause any issues. The small modulation depth and a snob index of 0% guarantees that it’s easy on the eyes. The light is not suitable for videoraphy though since the flicker will be visible on higher shutter speeds. Please note that the output is not visually stable even though there’s no inherent mains frequency related flicker. See below.
I don’t usually notice any problems with LED bulbs when run from the wall at my house, but with the Bedtime Bulb there was continuous visible output changes. When used for indirect lighting, it didn’t normally bother me, but when looking at a surface lit by the bulb it was very noticeable. The light is marketed for reading, but unless your wall AC is perfect it isn’t suitable for that purpose. I have no idea if the 120V version fares better in this regard, but the 230V version needs better filtering.
Here’s three plots visualizing the light output over time from an oscilloscope with different power sources over 24 seconds. The measurement was setup so that the inherent but visually invisible 100Hz flicker didn’t show up.
AC voltage from the wall. There’s some visible change in output every once in a while.
AC voltage from a pure sine wave inverter with a lot of high frequency noise (Omni Ultimate). The light output has very visible and irritating flickering.
AC voltage from a simulated/stepped sine wave inverter with stable output (Omnicharge). The output is perfectly flat.
AC power draw
Current is drawn in short pulses 100 times a second as the input voltage gets high. There’s a hint of power factor correction which results in the current waveform vaguely resembling a sinewave. The power factor varied from 0.77 to 0.82 during testing.
Cyan line: mains line voltage
Yellow line: current draw of the bulb
Violet line: power draw (voltage * current)
The Bedtime Bulb is a very warm and cozy light with beautiful tint and very good color rendering. As advertised there practically no blue light to affect your hormone levels at night.
The only drawback I experienced was the poor filtering on the driver. The output is very sensitive to AC line noise and changes in voltage. Changes in output were clearly visible in my testing from a wall outlet or noisy inverter but not when using a clean simulated sine wave from an inverter. For this reason I’m not sure I can recommend these. I haven’t tested the 120V US version and can’t comment on those.
Please note that the test was done when the bulb was brand new. I can’t guarantee that they will perform similarly after months or years of use.