We have tested 5 different models of pocket-sized USB LED night lamps and compared them to a common single candle stick.
USB LED Lamps Tests vs CANDLE Brightness Comparison
SMD LED Chips
SMD LED chips have greatly evolved over the past decade. They come in all different shapes and sizes you can possibly imagine.
Contemporary discrete LED chips are: 5050, 5630, 5730, 2735, 2835, 3528 and so on. First 2 digits denote width; second 2 digits denote length (all units are in 1/10th of a millimeter or mm, for short).
- 5050 LED chips are 5.0 x 5.0 mm in size
- 3728 LED chips are 3.7 x 2.8 mm in size
- 5730 LED chips are 5.7 x 3.0 mm in size
The main LED chip properties are:
- Energy efficiency – depends on Lumens per Watts ratio. Despite popular belief, maximum power efficiency of a LED chip is achieved at much lower power level than its maximum power rating! Lumens per Watts vs Forward Current (Amps) chart has approximately a shape of an exponential decay curve. For this very reason, many energy efficient designs incorporate at least 30-100 % more LED chips than absolute minimum, to avoid lower efficiency, keep chips cooler, and drive them at “sweet spot”.
- Beam width (2D or 3D angle of emitted light rays). Typically controlled by chip geometry and shape of focusing lens on top, which can be added later after basic chip manufacturing process. Lens introduces 5-10 % drop in lumens output (efficiency loss), depending on its optical transmittance value, which is usually around 90-95 %.
- Lumens output per single chip. It depends on power rating and efficiency.
Typical values for a 5050 LED chip are:
- 200 mW (0.2 Watts) Maximum Power Rating
- 120° degrees beam width
- 8~14 lumens per single LED chip, but it may be as high as 24
Please, keep in mind that data varies by manufacturer, class (price), application, and also changes with each new generation of LEDs; consequence of a rapidly developing industry. Cheaper (low power) ones usually find their usage in products such as USB LED lamps or LED strips we are testing today. More expensive ones are reserved for a higher class of products, with their respective price. But, higher power and light output (lumens) translates into more battery power required to drive them (and, consequently, generated heat), which is something of a luxury and design constraint in miniature portable devices and applications.
LED chips also come in different power and operating voltage ratings, too. Although, this is mainly achieved by additional controller and resistor network circuits, or stacking chips in series, resulting in operation at higher rated voltage than nominal LED silicon excitation values.
Common modern SMD LED of white, blue or RGB color operates under 2.7 ~ 4.2 Volts (matches modern Lithium-based or 2 (or 3) x AA/AAA standard batteries), but there are also other variants: for 5 Volts (USB bus powered), 12-24 Volts (car/truck accumulator powered and in common household lighting applications), and all the way up to mains 110-220 V AC grid power supply (home-office-industry use). Voltage boosters or step-down converters are used to either boost lower voltage (1-3 volts) into higher one (5-12 Volts), or rectify and scale down mains power supply.
LED chips are non-linear electronic components (V-I curve), very much like their ordinary non-light-emitting relatives, which means that their light output performance greatly varies with the variation of input voltage. This makes very little concern in applications such as portable battery-powered LED lamps, but in professional and home lighting applications, it is of a great importance. This is why constant-current driver circuits should be used, since LED brightness can be controlled more linearly by the amount of electrical current passing through the chip.
Last, but not least, COB (chip-on-board) is the latest and greatest trend among LED lighting world, breaking away from traditional discrete packaging and densely packing as much integrated chips as possible on an arbitrary shaped area made of insulation layer and aluminum substrate (heatsink): circle, square, rectangle, moon-shape, star-shape…
Note that basic aluminum substrate provides bare-bone short term COB cooling, and much larger heatsink must be added separately.
USB LED Lamps
USB LED lamps tested here are very lightweight, extremely portable, and cheap – each one costing around $1 USD dollar, or so. They are very handy, we use them with portable external power bank on a regular basis for various tasks, and they can also help a fellow photographer to achieve a more natural look of their subjects, or to avoid the built-in flash (or even combine flash with additional lighting source for maximum effect!). Particularly suitable models for additional lighting in photography are aluminum models with plastic diffuser on top, so that subject appears evenly illuminated.
Advantages over the traditional common candle are numerous. So much, in fact, that we were absolutely astonished how inefficient and dim candle light appears in contrast to modern LEDs! Ah, those were the days… when humans at night lived in darkness filled will little glimpses of light here and there. Although, at least, they had stars on the sky.
In any case, watch our video to discover how portable pocket-size USB LED Lamps perform, including basic calculations about LUMENS and CANDELA equivalents. In addition, we also tested their power consumption performance, which is important when run on portable batteries / power banks, and their thermal performance e.g. how much those USB sticks get hot after prolonged continuous use.