Osram Decostar 51S GU5.3 35W 12V 2900K 36° – dichroic reflector, dimmable

Requires a 12V transformer

This is a 12V low-voltage lamp that requires a 12V transformer to operate. The transformer converts the household 230V mains voltage to 12V. Compatible transformers (both electronic and magnetic) can be found in our selection under Electrical Supplies → Transformers category.

Check transformer power

The transformer's power must match the lamp's (or multiple lamps' total) power. For example, for one 35W lamp, the transformer must be at least 35W. For multiple lamps, calculate the total power and choose a transformer accordingly — it's often advisable to allow for a small reserve (e.g., two 35W lamps = 70W, choose an 80–105W transformer).

GU5.3 base — bi-pin fitting

GU5.3 is a two-pin (Ø 5.3 mm) base that is inserted directly into the luminaire holder. Not to be confused with a GU10 base, which is bayonet-fitted and operates on 230V mains voltage.

Cold light mirror — cooler light beam

The Decostar 51S's dichroic mirror reflects visible light forward but allows infrared heat to pass through the mirror to the rear. This means that the illuminated surface feels up to 66% less heat compared to a regular halogen lamp. Particularly useful in display cases, museums, art illumination, and food displays where heat can damage the objects.

Note: the rear of the lamp still heats up — ensure the luminaire is designed to dissipate heat from the rear.

UV filter — protects colors

The UV filter blocks UV radiation, which would otherwise fade colors in artwork, textiles, and products. This makes the Decostar 51S an ideal choice for museums, galleries, clothing stores, and display cases.

The lamp is dimmable

This Decostar 51S is 100% dimmable with compatible dimmers. Halogen lamp dimming is possible with both electronic and triac dimmers. Check that the transformer is dimmable if you want to adjust the light output.

Installation checklist

1. Check that the luminaire has a GU5.3 base (not GU10)
2. Check that a 12V transformer is used, with sufficient power for the total lamp power
3. Check that the lamp dimensions (Ø51 × 46 mm) fit the luminaire
4. Turn off the power before installation — do not touch the lamp glass with your fingers (grease can shorten its lifespan)
5. Install the lamp and turn on the power

Consider an LED alternative

If energy saving and longer lifespan are important, consider GU5.3 LED spotlight lamps, which use approximately 80% less energy and last up to 25,000 hours. However, halogen retains its advantages with perfect CRI 100 color rendering, which is important for illuminating artwork and jewelry, for example.