Unique Solid State Optical Scheme
Lumencor Light Engines are integrated arrays of solid state light sources. The number of sources in a single light engine can be as many as 8. The wavelength, bandpass, optical power and mode of operation of each source is selectable based on the application dictates. The solid state light sources are inherently stable and long lived. Lumencor’s modular light engine designs enable application-specific configurations in a way that incandescent light sources cannot. Combinations of different types of solid state sources (LED, luminescent light pipe or laser) with various spectral output characteristics can be assembled within the light engine framework according to application requirements. The novel, luminescent light pipe is a proprietary technology that provides high power broadband output in the 500–600 nm (green/yellow) wavelength range, circumventing the performance limitations of LEDs in this range (the so-called “green gap”). Like the spectral content, the output power of the component light sources can be engineered according to application requirements. The light sources may be activated individually, or as an ensemble producing white light output. Source activation and output attenuation is electronically controlled, providing faster and more reliable performance than incandescent light sources. No mechanical shutters, irises and filter switchers are employed. The main criteria to consider when determining which Lumencor light engine is most suitable for your application are:
- Is the light source to be used for transmitted light microscopy, fluorescence microscopy or another application?
- Do you want selectable color bands or white light output (or both)?
- What fluorophores should the light engine excite?
- Do you want onboard, manual or remote, computer-based controls?
- How do you want to direct the light output to your microscope and ultimately to the specimen (liquid light guide, optical fiber or direct coupling)?
With these criteria in mind, review our product portfolio for a comparison of our light engine products. We can provide numerous features and configurations not available in our standard portfolio products via OEM customization.
One of the main benefits of Lumencor’s solid state illumination technology is its capacity for precise electronic control of light output intensity, color and timing. Electronic control of Lumencor light engines is implemented via serial and TTL interfaces.
1. Numerals indicate the maximum number of individually addressable color outputs. W indicates light engines with white light output only. 2. TTL provides on/off control only. Definitions of Trigger and Gate protocols are given below. 3. Color (wavelength) selection is achieved by enabling/disabling individual solid state sources within the light engine. Therefore, the number of electronically selectable color bands is equal to the number of light sources (e.g. 4 for MIRA, 6 for SPECTRA X). 4. Output intensity can be set from 0–100% in 1% increments; however operation in the 0–5% range is not recommended. 5. TTL mode selectable via serial command. 6. Includes SOLA SE FISH light engines.
Serial control can be implemented from a variety of platforms:
|Control Hardware/Software||Further Information|
|Lumencor Control Pod||lumencor.com/products/other-accessories/controllers/|
|Lumencor GUI (Windows)||lumencor.com/resources/control-software/?section=S1|
|Third Party Microscopy Control Software||lumencor.com/resources/control-software/?section=S2|
The response time for serial commands depends on several factors including the host computer operating system, processor speed and serial port baud rate. Under typical installation conditions it is around 10–50 ms.
Measurements of SPECTRA X light engine output power (from 3 mm liquid light guide) in response to serial intensity control settings. Figures in parenthesis are bandpass filter center wavelength/full width at half maximum values in nanometers. All output color selections are electronically controlled except for green/yellow, which requires a manual exchange of bandpass filters.
TTL provides light output on/off switching but not intensity control. However TTL signals elicit much faster responses than serial commands. The fastest response times (~ 10 µs) are provided by AURA, SPECTRA and SPECTRA X light engines (see fast switching times). TTL control signals are typically derived from hardware peripherals such as cameras or digital acquisition (DAQ) cards.
|TTL Protocol||Operating Characteristics|
|Trigger||Active TTL signal1 enables individual light sources. Accessory break-out cable required. Serial source on/off settings should be in the OFF state. Source intensity remains under serial control.|
|Gate2||TTL signal gates light output on or off but does not enable light sources. Light sources must first be enabled by serial command or manual control.|
1. Active = HIGH or LOW depending on light engine configuration. 2. Also referred to as “electronic shutter.”
Fast Switching Time
Fast switching between color channels is a key requirement for applications such as multicolor fluorescence microscopy, optogenetics and “virtual color” transmitted light imaging. Switching via serial commands is limited to around 10–50 ms by factors including the host computer operating system, processor speed and serial port baud rate. Faster switching requires TTL hardware control, as implemented in the example below.
A. Alternating cyan (485/25 nm, ~0.5 ms) and green (560/32 nm, ~3 ms) output pulses generated by TTL triggering of an AURA light engine. Output traces recorded using an analog photodiode connected to a Velleman PCSU1000 oscilloscope. Cyan and green color bars identify the alternating color channel outputs recorded by the photodiode.
B. Selective attenuation of the cyan output via serial control.
C. Dual channel oscilloscope display of TTL control inputs. Blue trace = cyan channel control input, red trace = green channel control input.
Lifetime and Power Stability
When a light engine is returned to our facility for upgrades or other service, we routinely remeasure its power output and issue a new certificate of conformance to the customer. The chart below shows remeasured total output power for 18 SPECTRA X light engines expressed as a percentage of the values recorded at the time of original ship date. In all cases, the remeasured output significantly exceeds the 70% of the original level that the light engine is designed to maintain during its operational lifetime.
Output stability is critically important for consistency of data acquired during long periods of continuous operation. The plot below shows the total white light power output of a SOLA SM light engine, delivered through a 3 mm liquid light guide and measured by a thermopile detector, over 24 hours of continuous operation. The approximately 5% output power decrease in the first 12 minutes of operation (between the first green and red arrow marks) is due to thermal equilibration of the SOLA SM’s five solid state light sources. Thereafter, output variations are on the order of +/-10 mW (coefficient of variance = 0.32%).
Power at the Sample Plane
When evaluating light intensities required for widefield fluorescence microscopy, the quantity of most importance is the irradiance (aka power density) at the sample plane expressed in mW/mm2. The table shows irradiance generated by SPECTRA III and SPECTRA X light engines in the four principle excitation bands used in multicolor fluorescence microscopy. Irradiance levels required for widefield fluorescence microsopy are typically on the order of 1–100 mW/mm2. Clearly, such levels are provided by the SPECTRA X light engine, prompting the question of why would the higher irradiance levels provided by the SPECTRA III light engine be useful?. Although several reasons can be put forward, the most compelling is that higher irradiance levels allow exposure times to be shortened while maintaining the number of fluorescence photons detected. Shorter exposure times provide increased temporal resolution in time-lapse image sequences and reduce the time required to aquire multicolor z-stacks or slide scans.
Measuring Light Engine Power Output
This video demonstrates how to measure light engine power output for comparison with the benchmark values reported on the certificate of conformance and for quantitative assessment of liquid light guide performance.
Light Output Quantitation
The ability to control the input quantity of the light “reagent” is a critical factor in obtaining predictable and reproducible outputs from photochemical processes. Controlled light delivery for applications such as quantitative fluorescence microscopy, photodynamic therapy (PDT) photolithography and optogenetics requires intelligent light sources equipped with output monitoring and feedback systems. At Lumencor, we refer to quantitative light delivery as metered dosage. The necessary monitoring and feedback systems can be optionally installed in all SPECTRA, SPECTRA X and AURA light engine models. Open loop and closed loop metered dosage systems are available. In both schemes, an onboard photodiode continuously monitors the light output and generates a reference signal. In open loop monitoring, the reference signal is delivered for external display or processing via a BNC connector on the rear panel of the light engine. In the closed loop metered dosage scheme, the reference signal meters the light output and shuts it off when a user-input time-integrated intensity threshold is reached. All closed loop metered dosage functions are controlled from a serially connected computer.
Lumencor’s illuminators are designed to support the use of the most common fluorophores used in fluorescence microscopy today. Products come with multiple outputs designed to produce white light or multiple outputs designed to be used independently. SOLA light engine models® require filtering to be done by the end user; filters and mirrors are all external to the light engine. SPECTRA light engine® models contain excitation filters. The SPECTRA X light engine® affords the user the opportunity to switch excitation filters to suit different experimental requirements. The use of Lumencor’s recommended filters and matched dichroics and emission filters will ensure the most power and intensity is delivered to your instrument or microscope and will minimize any bleedthrough of excitation light into the emission bands. Please speak to your Lumencor sales representative or contact firstname.lastname@example.org to confirm the best filter prescription for your application and experiments. Fast switching speed is needed in illuminators designed to support live cell imaging and high throughput analysis. Lumencor’s products satisfy this need with electronic switching and shuttering between color bands and among intensities, on the order of 10’s of microseconds or less. This is in contrast to the 100 ms timing typically required to rotate a filter wheel between single-band pass filters for use with the common arc lamps. The fast source switching capability of Lumencor’s light engines can be fully exploited with appropriate multi-band dichroics and multi-band emission filters. They eliminate mechanical constraints of timing tied to filter movement on the detection side of the analysis. Please refer to the following data sheets for recommended single-band and multi-band filters sets for imaging widely used fluorophores on microscopes equipped with Lumencor light engines:
Low Cost of Ownership
The requirement for periodic replacement of bulbs is a hidden cost of mercury and metal halide lamps. Because the time and material costs of bulb replacements are often allocated to facility operating budgets, they tend to be overlooked in capital equipment purchase considerations. As shown below (Table A), replacing a mercury lamp with a SOLA SM light engine will not only bring an end to bulb replacement chores, but in just over two years the modest capital investment will have been recouped in saved operating costs. And the SOLA SM will still have about 80% of its 20,000–hour design lifetime left to run. Metal halide bulbs, although more expensive than mercury, require less frequent replacement. In this case (Table B), the purchase cost of a SOLA SM will be recouped after 6–7 years of operation.
Lower Power Consumption
In addition to eliminating bulb replacement costs, solid state light engines provide further operating economies in terms of electrical power consumption. Mercury arc and metal halide lamps typically require 30 minutes stabilization after ignition as well as a 30 minute cool-down period before restarting. Consequently, it is standard practice to leave the lamp running for the full duration of the imaging session, even though the light output is actually being used to acquire image data for only a small fraction of that time. In contrast, solid state light engines do not require stabilization and cool-down periods, allowing intermittent operation where light output is generated only when it is needed for data acquisition. Electronic light output control allows users to take advantage of this capacity to its fullest extent. Illustrative examples of energy savings provided by a SOLA SE light engine compared to mercury (A) and metal halide (B) lamps are shown below. Furthermore, the operating economies illustrated above continue to increase with advances in light engine design. A SOLA light engine manufactured in 2016 is significantly more efficient than a predecessor from 2013:
►SOLA SM Generation I (before August 2013) produced about 2 watts total white light output from 150 W electrical input
►SOLA SM Generation II (after August 2013) produces about 3.5 watts total white light output from 100 W electrical input