Illuminator Lamphouses for Olympus BH2 Microscopes
Click here to learn about the LS20H 20W halogen lamphouse for the BHT/BHTP/BHTU.
Click here to learn about the BHT/U_LED Illuminator from the Empire of Dirt Workshop.
Click here to learn about the BHS-LSH 100W halogen lamphouse for the BHS/BHSU.
Click here to learn about the BH2-ULSH45 50W halogen lamphouse.
Click here to learn how to properly center the 6V/20W halogen lamp in the LS20H lamphouse.
Click here to learn something to watch out for when buying 6V/20W lamps for the LS20H lamphouse.
LS20H 20W Halogen Lamphouse
The LS20H 20W halogen lamphouse was used on BHT/BHTP/BHTU and CK2 scopes and on the Ill-B/Ill-K stereo illumination bases. There were two distinct versions of the LS20H manufactured by Olympus. The early 5-LB402 version, which did not contain a lamp reflector, and the newer 5-S119 version, which included a concave reflector behind the lamp to increase the light output of the LS20H. The lamp reflector was added by Olympus as a direct response to their recognition that they were beginning to lose sales to the newer 30W Nikon scopes coming on the market back in the 1980s. In side-by-side comparison testing performed by the Empire of Dirt Workshop, the newer LS20H version with the lamp reflector provides about 45% more usable light than the early version without the reflector. This reflector puts it on par with a 30W non-reflector lamphouse used by Nikon.
The LS20H lamphouse utilizes a pre-centered 6V/20W ESB halogen lamp (Olympus 8-C405), with an average service life of 200 hours. Evident no longer sells the 8-C405 halogen lamp, but the Osram 64250-HLX, the Ushio JC6V-20W/G4, and the Philips 7388 are suitable equivalents.
Since the LS20H lamphouse operates at very high temperatures due to the 20W halogen lamp contained within it, the electrical contacts in the ESB lamp connector in the lamphouse will eventually oxidize to the point where electrical contact with the lamp pins will become impaired and the lamp will no longer reliably illuminate. Because of this, the LS20H should be considered a consumable part which will need to be overhauled or replaced whenever the electrical contacts within the socket become excessively oxidized.
Based on feedback from a few microscope service people who supported the BH2 in its heyday, a 20W halogen BH2 used eight hours a day would need a new LS20H every 4 to 5 years. For the average amateur microscopist, the replacement interval would of course be far greater.
The LS20H lamphouse is no longer available from Evident (as of 2025), so the supply of them on the used market is rapidly dwindling and the prices are quickly rising. Please do not throw these away when they go bad! The Empire of Dirt Workshop has a PDF showing the procedure to overhaul a tired LS20H lamphouse, along with the parts needed to successfully perform the repair. Alternatively, the Empire of Dirt Workshop can perform this repair for you, if you don’t wish to undertake such a project.
The point is, these lamphouses are as good as gold to a halogen purist, working or not, since the LS20H can easily be given a new lease on life!
An alternative to the LS20H halogen lamphouse is an LED retrofit. There are several such replacements available for the BH2 on the market, including the BHT/U_LED Illumnator from the Empire of Dirt Workshop.
BHT/U_LED Illuminator
The BHT/U_LED Illuminator is an LED-based replacement for the obsolete LS20H halogen lamphouse, which was developed by the Empire of Dirt Workshop in direct response the discontinuation of the LS20H lamphouse by Evident.
The BHT/U_LED is available in several versions (3W Neutral, 5W Neutral, and 5W Cool) for the BHT/BHTP/BHTU 20W scopes. Click here for details of the BHT/U_LED Illuminator from the Empire of Dirt Workshop.
BHS-LSH 100W Halogen Lamphouse
The BHS-LSH 100W halogen lamphouse was used on the BHS/BHSU/BHSP scopes. The BHS-LSH lamphouse utilizes a pre-centered 12V/100W halogen lamp (Olympus 8-C406), with an average lifetime of 2000 hours. Suitable replacement lamps include the Philips 7724.
BH2-ULSH45 50W Halogen Lamphouse
TBD
BH2-LSRF Fluorescent Lamphouse
TBD
How to Properly Pre-Center the 20W Halogen Lamp
Any microscope which employs pre-centered Köhler Illumination (and this includes the BH2) relies on the accuracy of the positioning of the filament within the lamp to provide optimal Köhler performance. In these pre-centered designs, there are no manual adjustments to allow the operator to center the lamp.
Many people do not know this, but when you install the 6V/20W halogen lamp into the LS20H lamphouse, there is a little bit of latitude as to how the lamp can be plugged into the socket, to allow the lamp filament to be properly positioned. The height can be varied slightly, and the lamp can be tilted one way or another, to allow the operator to position the lamp filament for proper centering.
This can be a difficult thing to do in the older LS20H lamphouses, since there is no easily visible feature with which to align the lamp filament. The newer lamphouses with the reflector behind the lamp do allow for this to be done. Simply plug the lamp in and tweak the positioning such that the lamp filament aligns with the small screw that holds the reflector in place.
See the image below for an illustration showing the proper filament position.
Make sure you do not get any skin oil on the lamp glass during this process, or the lamp may fail prematurely when it rises to operating temperature.
All Is Not Right In Halogen Ville?
The ANSI standard for the 6V/20W ESB bulb used in the LS20H lamphouse was based on lamps originally made by Philips and Sylvania (i.e., the Philips 7388 and the Osram 64250-HLX). So when it comes to replacement lamps for the LS20H, you can’t go wrong with either of these, right?. After all, these guys are the OGs of the ESB lamps! At least that’s what I used to think.
Frank Fisk, who does field service on Olympus/Evident scopes in the southwest US, showed me an interesting thing to be aware of regarding the 6V/20W ESB lamp used in the LS20H lamphouses used on the BHT/BHTP/BHTU and ILL-B/ILL-K stereo illumination bases.
The image below shows the 7388 on the left, and the 64250-HLX on the right. The filaments are precisely positioned in both lamps, per the relevant ANSI specification, but look closely at the glass envelopes of the two lamps. The bottom of the filament in the Philips 7388 is very close to the glass envelope, while the Osram filament is well positioned, relative to the glass.
The close proximity of the Philips filament to the glass has caused lighting issues in the field with the 7388 that are not present with the 64250-HLX. If you do use a Philips 7388 in your scope, you may want to raise it a little higher in the socket than would otherwise be called for, to achieve a more uniform field.
This is a good thing to know. Thanks, Frank
