Today we are testing an LED light source from Apture. According to the manufacturer, this light source has adjustable colour temperature and extremely good colour rendering performance. According to our test, this light source is probably the best light source in terms of colour rendering that we can found on market.
Adjustable colour temperature
Although colour temperature can be adjusted through post-processing, or even using the white balance settings of a camera. It would still be nice if we can make the colour temperature right during the shoot, especially for cinematography or if you are using films.
The following picture shows how colour temperature is adjusted. Basically the light source has two types of LEDs (5500K and 3200K), by adjusting the proportion of output of two LED types, you can get a output colour temperature between 5500K and 3200K. Note that the total light output remains almost constant during the adjustment, therefore you CANNOT make both LEDs deliver maximum output, that also make sense: If you do so, power consumption will be doubled, since this light source uses 100% passive cooling (no fan), then you may have serious overheating problem.
Background: What is CRI?
CRI means Colour Rendering Index, which represents how accurate the object’s colour can be rendered under a specific light source. To describe the theory behind it, I would like to quote a sentence from Wikipedia.
“Emitted light spectrum determines the CRI of the lamp.”
Spectrum means the intensity of light on a specific colour (wavelength). For tungsten halogen lamp and daylight, as they are very close to a black body radiator, they are defined as having a CRI of 100. While a Low-pressure sodium lamp has almost only “Yellow light”, they have the CRI of -44. CRI is especially important if your photo/film needs to well represents the colour of your object.
Optical test results
Following table is the raw data from Ocean Optics Spectrometer. Because this light source has an variable colour temperature design, we took measurements at 100% white (5500K) and 100% warm white (3200K).
CCT is the measured colour temperature of the light source, measured values (5475K 3298K) are slightly different when compared with technical specifications, but it’s within the acceptable range. Because accurately measuring colour temperature requires the individual LEDs being disassembled from the light source, and placed into an integrating sphere.
R01-R15 represents the ability of the light source on rendering different colours (Named test color samples according to CIE 1995), maximum value achievable is 100. We can see that only CRI R12 has lower value (Especially at 5500K, 75.9 is really not good), the rese are all above 95, meaning that this light source may have problem when the sample is Strong blue (TCS12) coloured.
Ra is the most important value that we need to focus on, some company also call it Color Accuracy. The official definition of Ra is the general color rendering. Ra is the average value of R1 to R8. Our results showed that this light source has extremely high Ra value on both colour temperatures (97.2 and 98.4) , even better than the company said it would be (>96).
|CRI R01:1002||97.1 (5475K)||98.2 (3298K)|
|CRI R02:1003||98.5 (5475K)||99.5 (3298K)|
|CRI R03:1004||97.5 (5475K)||97.7 (3298K)|
|CRI R04:1005||98.0 (5475K)||99.0 (3298K)|
|CRI R05:1006||97.2 (5475K)||99.2 (3298K)|
|CRI R06:1007||95.5 (5475K)||98.4 (3298K)|
|CRI R07:1008||97.0 (5475K)||97.9 (3298K)|
|CRI R08:1009||96.8 (5475K)||97.5 (3298K)|
|CRI R09:1010||96.6 (5475K)||95.2 (3298K)|
|CRI R10:1011||98.0 (5475K)||99.3 (3298K)|
|CRI R11:1012||97.8 (5475K)||96.8 (3298K)|
|CRI R12:1013||75.9 (5475K)||84.6 (3298K)|
|CRI R13:1014||98.3 (5475K)||98.4 (3298K)|
|CRI R14:1015||98.5 (5475K)||97.9 (3298K)|
|CRI R15:1016||96.6 (5475K)||98.4 (3298K)|
|CRI Ra:1001||97.2 (5475K)||98.4 (3298K)|
Measured power consumption is 8.64W at 3200K, 8.28W at 5500K. Meaning that if you are using a 7.2V, 1.8Ah battery, it will last 1.5 hours. If you planned to use it in a studio, I would suggest you do some modifications on the light source, like adding a DC input (you can use a 9V power supply).
The lamp we have tested in this article costs about 58 USD on Amazon. Since Apture offers a great numbers of products, actual price may vary depending on size, function and power. But overall, this is still an cheap and reliable product.