color-temperature-scale

What is colour temperature?

The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of a color comparable to that of the light source.

When the ideal black-body radiator is heated, the color of light it emits will change. This color begins as red in appearance and graduates to orange, yellow, white, and then blue-white to deeper colors of blue. The temperature of this metal is a physical measure in degrees Kelvin or absolute temperature. While lamps other than incandescent such as LEDs do not exactly mimic the output of this piece of ideal black-body radiator, we utilize the correlated color temperature (or Kelvins) to describe the appearance of that light source as it relates to the appearance of  a black body radiator.

Light is often referred to having a certain color temperature. Strangely, warm light is a lower color temp, and cool light, blue, is a higher color temp.

Here are some temps of some common light sources:

color-temperature-scale

LED driver technology

Direct Drive (DD)

Direct drive (DD) is the simplest and cheapest design. It is a direct path from the battery to the LED.

Sometimes there is a CPU and transistor to create different modes (25%, 50%, 100% …. etc.).

It is used when we want to make very powerful flashlights.

Advantages:

  • Cheap.
  • There is no flickering, so it is ideal for a video light.

Disadvantages:

  • Current is varying greatly with battery voltage. So the LED is dimming.
  • If there is a current limiter resistor, the efficiency is low (lower than a linear driver).
  • Voltage of the battery must be a bit higher than the LED voltage (generally ~3V) but not too much above. Othervise you can’t use this type of driver.

 

Linear Driver (LD)

This is the same as DD but with a “smart” resistor to limit current.

In this case the resistor value is not constant, it is continously adjusted by a linear regulator to make the current constant.

Most drivers use 7135 linear regulators (0.35A per piece).

Efficiency is varying with the battery voltage. The resistor burns off the extra power!

Eff.=Vled/Vbattery

Fully charged battery  Eff.=3.3V/4.2V=78%

Half charged: Eff.=3.3V/3.5V=94%

Discharged: Eff.=3.3V/3.3V =100%

When the battery voltage drops below Vled, the led starts dimming.

What happens if we use more batteries in series? The efficiency drops rapidly as more power wasted on the driver.

Advantages:

  • Simple and cheap design.
  • Constant current for most of the discharge of the battery.
  • There is no flickering, so it is ideal for a video light.

Disadvantages:

  • Voltage of the battery must be a bit higher than the LED voltage (generally ~3V) but not too much above. Otherwise you can’t use this type of driver.

 

Buck Driver

This is a more complicated design, also called as step down driver. It uses an inductor and capacitor to step down the battery voltage.Compared to a linear driver, the efficiency is more or less constant regardless of the battery voltage, which can be much higher than the LED voltage. The efficiency is between 70% and 90%.

An example would be using 4 li-ion batteries in series (16.8V ffully charged) to drive  3 series connect LEDs with a total Vf of around 13.2V. A buck driver will draw lower current from the input than what it will provide at the output. As the battery voltage drops, the buck driver will draw more current, but never more than the output current.

Advantages:

  • Can be used with battery packs that have a much higher voltage than the LED voltage.
  • Relatively high and constant efficiency.
  • PWM can cause problems for video or photograpy due to the relatively low frequency that is used. This low frequency PWM can ‘beat’ with the camera frame time to cause banding as the LED turns on and off within a single frame.

Disadvantages:

  • More expensive and complicated design
  • Voltage of the battery must be at least a bit higher than the LED voltage.

 

Boost Driver

This is a more complicated design, also called as step up driver.

This is very similar the the Buck Driver, but as its name implies, it will increase the voltage (Buck driver decrease the voltage).

It can also be used to power a multiple LEDs in series.

An example would be using 2 li-ion batteries in series (8.4V fully charged) to drive 4 series connect LEDs with a total Vf of around 13.2V. A boost driver will draw higher current from the input than what it will provide at the output. As the battery voltage drops, the boost driver will draw even more current and this tends to put more strain on a battery pack that is already fairly discharged.

Advantages:

  • Can be used with batteries that have a voltage lower than the LED voltage.

Disadvantages:

  • More expensive and complicated design
  • Voltage of the battery must be lower than the LED voltage.
  • PWM can cause problems for video or photograpy due to the relatively low frequency that is used. This low frequency PWM can ‘beat’ with the camera frame time to cause banding as the LED turns on and off within a single frame.

 

Buck Boost Driver

Combined buck-boost drivers tend to be less efficient that a straight buck or boost driver. Where a typical buck or boost driver can run at 90% efficiency (or higher) a buck-boost would likely be around 80%. There are some efficient buck/boost designs, but they cost more to manufacturer.

color-temperature-scale

Mistral XM-L2 technical dive light

Mistral xm-l2

  • Delivering breakthrough lumen output and efficacy in the XM package, the XLamp® XM-L2 LED is the highest-performing, commercially-available, single-die LED. Built on the SC³ Technology Platform. The XM-L2 LED offers the unique combination of high efficacy and high lumen output at high drive currents.
    • Max. power 10 W
    • Max. light output 1198 lm
    • Color temperature 6500 K
  • High quality reflector
    • FWHM 4,9°
  • High quality black anodized aluminium light head that optimizes head dissipation and protecting LED electronics and optics
  • Constant current („PWM less”) LED driver
    • PWM-less  CC (constant current) approach  gives  best  lm/W  from LEDs,  generates  no  acoustical  nor  EMI noise  and  enables longer runtimes compared to PWM CC or DD drivers.
    • Calibrated internal voltage reference and temp. sensor
  • Programmeable light modes (5 mode groups)
    • 100%
    • 50% 100%
    • 25% 50% 100%
    • 33% 66% 100%
    • 10% 50% 100%
  • Off-time mode memory
  • Dual Low Voltage protection
    • 2-step low voltage protection 
      • 2 step voltage protection based on accurate calibrated internal voltage reference. When battery voltage drops below 3.0V, light will blink 5 times and LVP step 1 becomes active. Driver will reduce/limit current to 25% of max. current if current mode level is higher than 25%. Modes lower than 25% would work as usual. When battery voltage drops below 2.8V (LVP step 2), the integrated battery BMS goes into shutdown mode.
    • Battery pack integrated LVP, over charge, over current, low voltage and short circuit protection
  • 2-level depth configuration menu with back/cancel option –possibility to change many settings without leaving configuration mode
  • Adjustable current via user interface: 0.125 Amp steps between 2A and 3A
    • This can be useful not just for fine-tuning LED current, but for example to reduce current consumption of all modes if longer run-times are needed for some reason. All modes are scaled down by same percentage, so overall mode current percentages remain the same.
  • Piezo switch
    • Solid stainless steel body
    • Sealed to IP69K
    • Easy to clean metal surface 
    • Long life (million cycles) 
  • Adjustable laser cutted stainless steel goodman handle with snap bolts option
  • Nickel plated IP69K rated brass AGRO cable glands
  • High quality black anodized aluminium canister body and lid
  • 17500 mAh Li-ion battery pack with integrated BMS system
  • Dual o-ring protection
  • Gold plated banana plugs
  • Stainless steel Nielsen latch
  • Every light is tested at 20 bar (~200 meter) for 60 minutes

Not available now. It is under construction and test.

Mistral XM-L2 optical performance

color-temperature-scale

What is the difference between Lumens, Lux, Watt, Lumen per watt and color temperature?

When buying a new dive light, it is easy to get confused about the different terms that are used to describe the most important parameters of the light.

LUMENS

Lumen is a unit of light, which is also known as Luminous flux. Lumens (lm) are a measurement unit, which tells what the total amount of light emitted from a dive light. You can roughly say that the more Lumens the brighter the light.
When we specify our dive lights, we use Lumens to see the total amount of light output. But Lumens will only show us a part of the picture. Producing a perfect beam shape does not reveal enough information to show us how the light output is created. For this we need a lux meter.
To measure the total amount of lumens, an integrating sphere is necessary. An integrating sphere (also known as an Ulbricht sphere) is a hollow, spherical chamber coated internally with a high reflectance coating that exhibits diffuse reflectance. Spheres are used as directionally-insensitive collectors of light when combined with photodetectors. An internally illuminated integrating sphere emits a field of spatially and angularly uniform luminance or radiance which is perfect for testing led lights.

LUX

Lux (lx) is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. One lux is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface.

Lux is much easier to measure than Lumen. Lux can be measured with a hand held device.
If the light output is focused on a small area (narrow beam), we see this as very bright light. If the light output is focused on a greater area (wide beam), we experience this as a weaker light.

WATT

Watt (W) is a derived unit of power in the SI units, defined as 1 joule per second and can be used to quantify the rate of energy transfer. It shows how much energy the product consumes, not how much light output (lumens) it provides. For this reason you should not only look after the amount of watt consumed, when select a dive light. It will just tell you how quickly it will drain your battery, and not how much light it produces.

LUMINOUS efficacy

Luminous efficiency is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt  (lm/W) in SI unit.

COLOR TEMPERATURE

The color temperature of a light source is the temperature of an ideal black-body radiator that radiates light of a color comparable to that of the light source. Color temperature is conventionally expressed in kelvins (K) is the SI unit.

Color temperatures over 5000 K are called “cool colors” (bluish white), while lower color temperatures (2700–3000 K) are called “warm colors” (yellowish white through red). “Warm” in this context is an analogy to radiated heat flux of traditional incandescent lighting rather than temperature. The spectral peak of warm-coloured light is closer to infrared, and most natural warm-coloured light sources emit significant infrared radiation.

The Sun closely approximates a black-body radiator. The effective temperature, defined by the total radiative power per square unit, is about 5780 K. The color temperature of sunlight above the atmosphere is about 5900 K.

color-temperature-scale

Shape of a Light Distribution Curve

In illumination engineering it is very important to see the total shape of the light distribution curve. A light distribution curve is a 2D- or polar diagram -characterization of the performance and it tells for an experienced eye what in detail to expect of the component, e.g., how narrow the light distribution is, are there any discontinuation points to be expected (shadows) or what the relative intensity is in HV 0 degree vs. 30 degrees.

A Full Width Half Maximum (FWHM) angle has been defined, in relative terms, for a symmetrical optics with its maximum intensity in the middle of its light distribution (horizontal and vertical 0 degree), to be the angle, where the intensity of illumination has dropped to 50% from its maximum peak value. Furthermore, many advanced companies define a further so-called 10% value, which is the angle, where the intensity of the illumination has dropped to 10% of its maximum peak value. This is a very useful parameter, e.g., when specifying optical components with an extremely narrow light distribution. The closer the 10% value is to the FWHM value the more light is really focused in the important narrow beam and the less stray light you have outside of the main beam. Now, one may wonder, why to use two values for a component, FWHM and 10% value, why is not FWHM itself sufficient? The reason is that FWHM value is not unambiguous, and it can even be misused to mislead a person specifying his system.

Let’s take a simple example with imaginative lenses A and B.

FWHM value does not give unambiguous information of an optical component.
These two lenses have the same FWHM value, but they perform in a very different way

 

Lens A is a lens with relatively bad optical efficiency and additionally, a proportionally big share of light falls outside of the centre beam area, i.e., its 10% value is a wide-angle value. Due to the shape of its light distribution curve – a flat curve with no really high peak in the middle, but more or less a “hill” type of a shape – it still has a FWHM value of +/- 5 degrees.

The other lens, Lens B, is a lens with high optical efficiency, with very concentrated beam and a narrow-angle 10% value. Its curve shape reminds of a Himalayan mountain instead the hill for lens B. The surprising fact is that this lens has the same FWHM value of +/- 5 degrees, as lens A. How can it be possible? Putting the absolute (not relative) curves of these 2 lenses on top of each other in the same diagram, shows that lens B gives 5x the light than lens A, but still the FWHM values are identical! The conclusion of this simple example is that different lenses cannot be compared against each other just using FWHM values. FWHM does not give the answer to the question how much absolute light is distributed in the specified angle or area. More facts are needed, 10% value already gives a good hint of how an optical component performs.

 

Source: Tomi Kuntze, President, LEDIL Oy

color-temperature-scale

Hurricane XHP-70 technical dive light

Hurricane XHP-70

  • Powered by Cree’s groundbreaking SC5 Technology™ Platform, the XLamp® XHP70 LED is a member of Cree’s Extreme High Power (XHP) class of LEDs that redefines lumen density and reliability.
    • Max. power 32W
    • Max. light output 4022 lm
    • Color temperature 6500 K
  • High quality reflector
    • FWHM 15°
  • High quality black anodized aluminium light head that optimizes head dissipation and protecting LED electronics and optics
  • Constant current („PWM less”) LED driver
    • PWM-less  CC (constant current) approach  gives  best  lm/W  from LEDs,  generates  no  acoustical  nor  EMI noise  and  enables longer runtimes compared to PWM CC or DD drivers.
    • Calibrated internal voltage reference and temp. sensor
  • Programmeable light modes (5 mode groups)
    • 100%
    • 50% 100%
    • 25% 50% 100%
    • 33% 66% 100%
    • 10% 50% 100%
  • Off-time mode memory
  • Dual Low Voltage protection
    • 2-step low voltage protection 
      • 2 step voltage protection based on accurate calibrated internal voltage reference. When battery voltage drops below 3.0V, light will blink 5 times and LVP step 1 becomes active. Driver will reduce/limit current to 25% of max. current if current mode level is higher than 25%. Modes lower than 25% would work as usual. When battery voltage drops below 2.8V (LVP step 2), the integrated battery BMS goes into shutdown mode.
    • Battery pack integrated LVP, over charge, over current, low voltage and short circuit protection
  • 2-level depth configuration menu with back/cancel option –possibility to change many settings without leaving configuration mode
  • Adjustable current via user interface: 0.250Amp steps between 4A and 6A
    • This can be useful not just for fine-tuning LED current, but for example to reduce current consumption of all modes if longer run-times are needed for some reason. All modes are scaled down by same percentage, so overall mode current percentages remain the same.
  • Piezo switch
    • Solid stainless steel body
    • Sealed to IP69K
    • Easy to clean metal surface 
    • Long life (million cycles) 
  • Adjustable laser cutted stainless steel goodman handle with snap bolts option
  • Nickel plated IP69K rated brass AGRO cable glands
  • High quality black anodized aluminium canister body and lid
  • 17500 mAh Li-ion battery pack with integrated BMS system
  • Dual o-ring protection
  • Gold plated banana plugs
  • Stainless steel Nielsen latch
  • Every light is tested at 20 bar (~200 meter) for 60 minutes

 

Hurricane XHP70 optical performance