Advanced LED Lighting - Max-i Fieldbus

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Advanced LED lighting
Integrated LED controller
The Max-i controller includes a state-of-the-art LED controller with a lot of outstanding features:

  • Suitable for even very demanding stage light and architectural lighting applications.
  • DMX512 and RDM replacement with up to 1022 DMX channels and an unlimited number of DMX universes (identifiers) on the same bus.
  • Can be driven directly by DMX512 controllers if automatic flow control is added, which may be simple to do in hardware.
  • Possibility to address each lamp by means of both implicit messages and group messages with separate channel specification for each type.
  • Full multiple master capability with possibility for any number of lighting controllers and lamps with event driven status indication on the same bus. RDM is a single master system, which must use time to poll the status of the lamps. This is highly inefficient, and it cannot be prevented that a single error may cause the loss of all light, which is the last thing you want during a concert apart from losing the sound.
  • Much higher efficiency than DMX512 because it is not necessary to transmit all data all the time at a high rate to avoid flicker. The data for each lamp may either be:
      • The wanted color and/or light level plus a common variable smoothing time (bypass, 2.7 ms, 5.4 ms, 11 ms, 22 ms, 43 ms, 86 ms plus up to 2.7 s on small changes in light level). Since each color channel has a 3rd order smoothing filter, this can reduce the necessary number of telegrams per second considerably. With for example the 86-ms filter, it is only necessary with approximately 12 messages per second to avoid flicker. It also makes it very easy to make short, but smooth light flashes with different rise and fall time by means of only two telegrams. This may be very handy to soften stroboscopic lamps and to drive lamps directly from microphones on each drum in a drum set (multiple master capability). With DMX512, the refresh rate is only 44 Hz if all 512 channels are utilized so in practice it is only possible with approximately 300 channels to avoid flicker (75 Hz).
      • 6 user defined functions with the same number of bytes as the color selection. This may be used for less frequent settings like lamp direction (pan/tilt), movement speed, zoom/focus, gobo index/rotation, special effects etc. If 6 (combined) functions are not enough, the user can just include a subaddress in the data field of one or more of the functions and in this way expand the number to the requirements of even the most advanced lamps.
  • Much highere safety than DMX512. DMX512 does not even have a single checkbit and is therefore very questionable to use for pyrotechnics etc., but Max-i is on the contrary designed for safety applications up to IEC 61508 SIL 3 (death of 1 - 3 persons) without additional layers.
  • Precise lamp synchronisation in the µs range. DMX512 updates each lamp when its data is received and therefore never at the same time as other lamps.
  • No need for termination resistors. This makes the installation easier and more reliable as many forget the resistors from experience.
  • No need for DMX splitters with or without expensive RDM extension. DMX cannot handle more than about 32 lights before it starts to have problems and it is often recommended to stick to around 16 to 20 fixtures. Max-i can handle several hundreds.
  • Unlike DMX512, the communication speed can be optimized after the line length, and due to the lack of termination resistors, it is possible to use reflected wave switching to enable very long distance communication on thin cables and/or star topology, which may be very useful for example for lighting on highways, bridges and tunnels up to approximately 20 km. The maximum length of DMX512 is only 300 m with RDM and 460 m without.
  • Pulse code modulation (PCM) with 1.25 µs pulses. This has a lot of very important benefits compared to the usual Pulse Width Modulation (PWM):
      • Only very small decoupling capacitors are needed.
      • No flicker or stroboscopic effects.
      • No discomfort. PWM below 800 - 3000 Hz may create headache, nausea, eye exertion and eye fatigue even though the flicker is not directly visible.
      • Maximum LED life. A LED chip is extremely small and therefore often heats up and cools down in less than a millisecond! If PWM is used, this causes mechanical stress due to the alternating expansion and contraction, and because the lifetime of a LED is an exponential function of the temperature, the reliability is reduced even more. The lifetime is approximately 200,000 x e-0,07T hours so that it is approximately 50,000 hours at 20°C and falls to the half for every 10° more, so if for example the chip temperature varies lineary between 30°C and 70°C in each PWM cycle, the lifetime will be less than 74 % of the lifetime with PCM, which keeps the temperature virtually constant at 50°C for the same power dissipation and cooling. This also makes it much easier to predict the degeneration of the LED's as a function of time and temperature and automatically compensate for that, because the temperature can just be measured on a common heat sink. With PWM, it is necessary to integrate much faster and measure the temperature directly on a die for each color to get a reasonable accurate prediction, but this is usually impossible.
      • It makes it possible to drive the LED's directly from a switch-mode converter in continous conduction mode without flicker due to interference between the switching frequency and the PWM frequency. In this mode, the currents to the LED's are not switched off when no light is wanted. Instead, the LED's are short circuited and the currents keep flowing through the switches, which however only dissipates very little power if the voltage drop is low. This maximizes the efficiency, but also increases the reliability as no capacitors are needed on the secondary side. Capacitors exposed to alternating currents must be considered wearing parts with a limited lifetime so one of the design goals of Max-i is to avoid this as much as possible. In many cases, it is the driver and not the LED's, which has the lowest reliability.
      • No violation of the Signify (Color Kinetics and the former Philips Lighting) PWM patent for color changing (RGB) lamps with communication.
  • No violation of the Infineon sigma-delta patent.
  • 4 x 8-bit, 6-color RGBWaAaC system with automatic generation of artificial amber (aA) and artificial cyan (aC) on the basis of RGB. Pure RGB-light has a terrible Color Rendering Index (CRI) of only approximately 25 % because there is almost no light in the yellow/amber and cyan ranges, so objects with these colors look way too dark.
  • 6-bit dot correction on each color in steps of 0.8 % from 0 to -48 % removes or reduces the necessity for expensive bin selected LED's. This reduces the price of lamps suitable for architectural lighting where color consistency is of utmost importance, and it is very easy to calibrate the lamps from time to time.
  • Build-in gamma correction of 2.44, which increases the contrast ratio and follows the sensitivity curve of the eye within ±1 % so that dimming does not cause any visible change in color hue and duty cycle as it is the case with both linear and exponential dimming *).
  • Contrast ratio of over 11,000:1 with a gamma of 2.44.
  • Extra white and lime/amber channels with a gamma of 1.56, which may be used for dim-to-warm or to control the LED current for RGB or white lamps and in this way increase the contrast ratio even more (gamma = 4).
  • Integrated one-button (toggle), two-button (up/down) or "analog" (quadrature encoder) light dimmer with 54 levels, night light, programmable start level and synchronized multi-way landing switching.
  • Possibility to control two lamps or group of lamps from one controller so that Max-i can replace ordinary dual wall switches without limitations, but with a lot of added features including light dimming and group-off and group-on.
  • Group up/down or analog daylight control with slow smoothing filter to convert the 54 levels to 216 steps and in this way make each step invisible.
  • Group 255 all-off, back-on and programmable emergency color for each lamp, which may be activated temporary in case of a communication failure and manually by means of a panic button.
  • Perfect for circadian light.
  • SPI interface to transfer non-light data for (mechanical) functions like pan and tilt, focus and zoom, gobo selection and rotation etc. to a connected microprocessor for handling.
  • Perfect for do-it-yourself garden lighting and for pools due to the low voltage of 20 V (without mains plus dimming).
  • Integrated traffic light controller with dimming, programmable minimum level and green safety output.

*) The sensitivity curve of the eye has been determined to be R = 9.033i for i ≤ 0.008856 and R = 1.16×(i^1/3)-0.16 for i > 0.008856. For most practical applications such as TV sets, computer monitors and LED lighting, this may be simplified and has been standardized according to ITU-R BT.1886 to R = i^(1/2.4) for a reference monitor where 2.4 is called the gamma factor. With the 8-bit input N = 127 (half), linear dimming gives a light intensity of 49.8 % (127/255), which the eye perceives as R = 76 %! With Max-i, the light intensity becomes 19.2 %, which the eye perceives as R = 51 %. This is very close to 0.498^2.4 = 18.8 % for a reference monitor. With exponential dimming such as the one used in DALI and CAN FD Light, the intensity is 3.16 %, which the eye perceives as only R = 21 %! For DALI it is: i = 10^(((N-1)/(253/3))-1) = 3.12 % => R = 21 % and for CAN FD Light it is: i = 0.9471^((255-N)/2) = 3.09 % => R = 20 %. Without a gamma correction close to the eye curve, the color hue and the duty cycle of a flashing lamp is changed as shown below:

If the gamma is lower than 2.44 – for example linear, a medium level orange color, which consists of more red than green, may seem reddish to the eye if the level is reduced and yellowish if the level is increased, and in case of flashing with a smoothing filter, which creates a ramp, the duty cycle seems to be increased. This is not acceptable for example for control lamps, which typical use a 50 % duty cycle. I case of a gamma higher than 2.44 such as for example exponential dimming, the opposite is the case.

The very advanced controller has previously unseen control possibilities. Without changing the settings, a lamp can simultaneously be controlled and dimmed by means of wall buttons and automatic daylight control, be set to a specified color for example by means of a mobile phone or tablet and be controlled together with other lamps in a common group telegram with individual reception delay to set a scene or even control the lamps in real time from for example a TV set or a computer with the same speed and performance as professional stage light.

With the 6-color RGBWaAaC system, which can generate excellent pastel colors, and the possibility to address many light sources in the same telegram, the lamp controller is perfect for circadian light and for illuminated ceiling panels with diffused light where it can create an illusion of being outside with drifting clouds and varying color temperature depending on the time of the day. This may for example be used to create a pleasant feeling in stores, treatment rooms in hospitals and in rooms without daylight such as rooms in the basement. The ceiling may simultaneously hide alarm sensors etc., which can just be connected to the same bus.

If 6 colors are not enough, any number of Max-i controllers can very easily collaborate by means of common telegrams. Just two controllers where the reception in one is delayed 4 bytes can create an absolute state-of-the-art 8-12-color system at a previously unseen low cost. With for example a royal-blue, blue, artificial cyan, green, lime, artificial amber, orange, red and deep red system, any color and color temperature can be created with excellent accuracy for example for lighting in art museums etc. Because of the inherent possibility for battery backup, the lamps for such applications can simultaneously be used for emergency lighting, which can even show the way to the nearest exit by means of running light for example controlled by means of a common group telegram. In case of smoke where white light gets scattered, the light may even change to red or reddish, which makes it easier to find the way out. If the lamps are equipped with sensors, they can simultaneously be used for alarm systems for example for burglary and fire so that only a single lamp unit may do it all.

Comparison between DALI-2, KNX-TP and Max-i

 Multiple master bus (with bitwise
 bus arbitration)
Need controller
 Publisher/Subscriber modelNoOnly group
 Direct communication from buttons to
 one or more lamps without controller
NoYes, by means of
group messages
 Dimming with gamma correctionEksponentialLinear2.44 = eye curve
 Max. number of devices per segment6464Several hundred
 Max segment length300 m700 m, 350 m
after choke
5.6 km, >20 km
with reflected
wave switching
 Time to send different data to 64
 monochrome lamps on a 300 m line
1.5 s at
1.2 kbps
(2.4 kBaud)
0.54 s at
9.6 kbps
(28.6 kBaud)
46 ms at 167 kBaud
or 6.8 ms in a
common message
 Total number of device groups /
 groups per device *)
32 / 30255 / 1 with own
reception delay
 Number of addressable scenes *)1600
 Max. power on communication lines
4 W at 16 V
2 mA/device
4,8 W at 30 V
with choke
1 kW at 20 V
 Separate power supply lines needed
 for actuators and lamps
 Number of checkbits (safety)0820 + Hamming code
 Microprocessor needed in LED driverYesYesNo
 Product certification requiredYesYesNo
 Programming of new devicesVery difficult.
May require an
expert and
special tools.
addressing with
area, line and
Very easy by means
of serial number
or push button.
 Useable for other applications than
 lighting control such as alarm
 systems, access control and energy
 management (one bus for everything)
*) Due to the very low speed, DALI needs group addressing and scenes to ensure that many lamps in the same room are updated simultaneously to avoid the so-called "Mexican wave", which occurs if a separat message to each lamp is used. With Max-i (or KNX), this is not necessary because of the publisher/subscriber model where any number of lamps can subscribe to the same message and in this way be updated simultaneously, and the very high speed of Max-i makes it easy just to store any number of scenes in a controller and even control the light in real time from a TV-set. Note that in DALI and Max-i, group addressing is a supplement so that there are two ways to transmit data - in Max-i with separate byte delay specification for implicit messages and group messages when a common telegram is used. In KNX, the 16-bit group address is just an identifier of a multicasted parameter very much like the 12-bit or 31-bit identifier of a Max-i value.

**) Both DALI and KNX are power limited because they communicates by means of a more or less short circuit of the communication line. This limits the maximum current, which can be drawn from these lines to 1-2 mA per device and makes it impossible to decouple the line by means of capacitors, which makes it is impossible to switch any loads. Therefore, separate power supply conductors must be used for almost all devices, which may even make it necessary with a galvanic separation. With DALI, the power supply is current limited to 250 mA and it is therefore this current, which flows when the line is pulled from the idle state of typical 16 V down to typical 0 V during half of the Manchester coded bits. KNX uses the old EIB communication, where a 30-V power supply, which is serial connected with a double choke in parallel with some pulse limiting components, is pulled down to 24 V for 35 µs in each 0-bit and then released for the remaining 69 µs, which causes a flyback spike, which shortly raises the voltage to approximately 42 V.

Street Lighting
New non-dimmable street lights should be banned because of the huge energy savings that dimming makes possible. If for example the light is just dimmed to what the eye regards as half, the power consumption of LED-based lights is reduced to only 18 % due to the logarithmic characteristic of the eye! There are however some disadvantages:

  • Dimming increases the price of each lamp.
  • Simple dimming, which just reduces the supply voltage, is in practice only possible by changing the outlet on the power transformer. It is therefore only possible with a few steps, which therefore becomes very visible, and it also gives a fairly low dimming range and makes it impossible to dim each lamp individually, which should be possible. Research on street lighting and crime has found that improved street lighting reduces crime and can increase the number of pedestrians walking through an area as they feel more safe. It is therefore feasible that reducing the street lighting has the reverse effect. For this reason, dimming of each lamp should be individually controllable by means of sensors so that the light has a low energy efficient background level, which depends on the ambient light, but is then increased at the presense of cars, bycycles and pedestrians. These sensors may simultaneously be used to optimize the traffic light in smart cities, and running light ahead of a car may even be used to indicate the speed limit. If you exceed this, you will loose more or less of the light ahead depending on other cars.
  • When the light is reduced, the color temperature should be reduced too for the light to be pleasing. This is expressed in the Kruithof curve below (D65 is the daylight point):

If for example a 4000 K light only generates 15 lux on the street as it is often seen, the light appears way too bluish and may even destroy the night vision. For this reason, dim to warm with good suppression of the blue source light in a phosphor converted (white) LED is a must for high quality lighting.

With the advanced LED controller, Max-i offers the ideal solution to these problems:

  • Due to the very high efficiency of Max-i, the smoothing filter, which reduces the necessary messages per second to only 12, and the possibility to address many lamps in the same telegram, Max-i is for example able to individually control 100 lamps on a 2 km long 4x2.5 mm2 cable at a UART speed of 38.4 kbps. In this way, the light can be reduced smoothly if there are no people or cars, and it is even possible to show the speed limit by means of running light.
  • The very fast responce time down to 1 ms and the 255 lighting steps makes it possible to use street lighting as part of grid stabilization. Today, this is primary done by means of rotating machines, which can both generate and absorb energy very fast due to flywheel action, such as generators in thermal power plans and synchronous compensators. However, as an increasing number of such devices are replaced by wind turbines and solar parks with electronic frequency generation and even by private solar panels without any overall control, it becomes more and more difficult to stabilize the grid - especially because these new power sources cannot absorb energy. In case of a sudden loss of a big load, there may therefore be excess energy in the grid, which may cause the voltage and frequency to rise, but if this happens during day time, Max-i can fully or partially compensate by turning on the street lamps to an appropriate level very fast and then reduce the level as the current generation is reduced.
  • During the winter where it is dark when people come home and the dinner is prepared, Max-i may also compensate for the increased power consumption from typical 5 to 8 p.m. by reducing the street lighting. Due to the logarithmic characteristic of the eye, even a fairly large reduction is hardly visible. This compensation is of course not possible during summer where the street lights are not on, but the increasing number of solar panels and the much lower energy consumption for heating reduces the problem.

Automotive Matrix Headlamps
The same properties, which makes Max-i perfect for stage light, also makes it very suitable for matrix headlamps, which makes it possible to increase the safety considerably by travelling with permanent high beam and maybe also with permanent fog lamps without risk of dazzling oncoming traffic or any preceding vehicles. The light is controlled by means of a camera or a row of light sensors, which detects the light from oncoming vehicles and reflected light from road signs and dims the light in these directions so that neither the oncoming driver nor the driver himself are dazzled.

Some matrix systems splits the high beam into 5 reflectors, each one having a chip containing 5 LED's so that the light can be individually controlled in 25 directions. With Max-i, this could be replaced with 6 reflectors with each 4 LED's and a Max-i chip, and it is then possible to utilize the many outstanding properties:

  • Choice between linear or gamma correction according to the characteristic of the camera or the light sensors.
  • The publisher/subscriber model makes it easy for each headlamp to utilize the same messages, and all LED's can be controlled in a single telegram.
  • Because of the smoothing filter, it is not necessary with more than 10 - 15 telegrams per second so very little data processing is needed. Without these filters, the LED's need to be updated at least 75 times per second to avoid flicker, which can even cause epileptic seizures.
  • No flicker caused by interference between pulse width modulation (PWM) and vibrations.
  • The dot correction may be used to ensure the same light level in all directions.
  • The possibility for a programmable light level in case of a communication failure increases the error tolerance and safety.
  • Unlike other systems, where each LED strips off the used bytes and then transmits the rest of the telegram to the next LED's, Max-i is a parallel system, so the communication line does not need to be broken and a failure on one chip does not affect the operation of others.

This page is created with WebSite X5 and updated May 31st 2024

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